This is only a preview of the February 2010 issue of Silicon Chip. You can view 17 of the 104 pages in the full issue, including the advertisments. For full access, purchase the issue for $10.00 or subscribe for access to the latest issues. Items relevant to "An OBDII Interface For A Laptop Computer":
Items relevant to "A Milliohm Adaptor for Digital Multimeters":
Items relevant to "Internet Time Display Module For The WIB":
Items relevant to "A Multi-Function GPS Car Computer, Pt.2":
Items relevant to "Precision Temperature Logger & Controller, Pt.2":
Articles in this series:
Purchase a printed copy of this issue for $10.00. |
A Look At Automotive
On-Board Diagnostics
You may not know it but your late-model car has an astonishing
array of sensors to make sure that its engine and electronic
systems all run at peak efficiency, while keeping emissions to a
minimum. This increasing use of electronics in vehicles has also
lead to improvements in the way a vehicle can be maintained.
With On Board Diagnostics (OBD), the performance of critical
engine components can be easily monitored.
By JOHN CLARKE
A
LL NEW CARS sold in Australia
from 2006 onwards are required
to comply with the Australian Design
Rules (ADR) to include On-Board Diag
nostics. This is called OBDII and the
“II” indicates that this is the second
generation OBD standard.
OBD is not new and has been around
for more than 20 years. The first OBD
standard adopted in California (USA)
was introduced primarily to monitor
the condition of vehicle emission
sensors.
Early OBD systems included a Malfunction Indicator Light (MIL). This
used a rudimentary blinking light system where the number of blinks could
be counted. This blink count could be
cross-referenced against a list to find
the problem indicated. Over the years,
there have been many refinements and
improvements.
The latest OBDII standard is far
10 Silicon Chip
more complex and includes a data
link connector for connection of an
OBDII scan tool which can be a dedicated hand-held unit. Alternatively,
it may connect to a laptop computer
via a cable that includes some form of
signal processing and which is used
in conjunction with special software.
Either approach can be used to retrieve
information from the vehicle.
On-board diagnostics are possible
due to the computer systems in modern cars. Most readers would know
about the car’s ECU (Engine Control
Unit) which is dedicated to controlling
such components as fuel injectors, the
exhaust gas recirculation (EGR) valves
and the ignition timing. Computerised
engine control is vital to ensure optimum fuel efficiency.
The ECU is not the only computer
system within a vehicle. There are
others that control the anti-lock brak-
ing system, stability control, cruise
control, air-bag activation, climate
control, central locking and even
the sound system. Many of these
computers communicate with each
other, swapping data as required.
With OBDII, communication is also
available via the scan tool to provide
vital information about the health of
vehicle components.
A diagram showing the input sensors connecting to the ECU and controlling the injectors and ignition is
shown in Fig.1. The OBDII scan tool
shows a sample of the diagnostics information available when attached to
the OBDII data link connector.
Modern engines are exceedingly
complex, making it difficult to diagnose problems if anything goes wrong.
There is an incredible array of sensors
or monitors, including those for camshaft position, turbo bypass valving,
siliconchip.com.au
AIRFLOW METER
COOLANT TEMPERATURE
CRANKSHAFT ANGLE
ENGINE RPM
INTAKE AIR TEMPERATURE
KNOCK SENSOR
MAP SENSOR
OXYGEN SENSOR
THROTTLE POSITION
VEHICLE SPEED
MALFUNCTION INDICATOR
LAMP (MIL)
INPUTS
ENGINE
CONTROL
UNIT (ECU)
OUTPUT
CONTROL
IGNITION
INJECTORS
EGR VALVE
CONNECTING
CABLE
OBDII DATA
LINK CONNECTOR
OBDII PLUG
Fig.1: the engine management unit (ECU)
accepts inputs from a range of sensors and
controls the ignition timing, fuel injectors and
EGR valve. The OBDII scan tool plugs into
the ECU and displays a range of diagnostic
information to aid troubleshooting.
intake and outlet valves, fuel and
oil pressure, injector operation, fuel
pump operation, turbo boost, ignition
misfire, ignition timing, cooling fan
operation, air-conditioning refrigerant, battery charging, transmission,
speed, RPM and automatic transmission functions.
When there is a problem, the ECU
can easily detect this because the
engine sensor results will not be as
expected. This is where on-board
diagnostics becomes invaluable in
making available the information from
the ECU. Major problems are indicated
with the Malfunction Indicator Lamp
(MIL) or in severe cases, the lamp
will flash.
As mentioned, the scan tool plugs
into the ECU’s Data Link Connector
(DLC) which is located inside the
vehicle. This connector is usually on
the driver’s side of the car under the
dashboard, behind the ashtray, near
the steering column or in the central
gear-stick console area. A workshop
manual will show where the connector
is located if it is not easily found. For
the scan tool to work, the vehicle must
be OBDII-compliant and use specified communications protocols – see
the section headed “OBDII Data Link
Connector” for more detail.
OBDII
SCAN
TOOL
DISPLAY
DIAGNOSTIC TROUBLE
CODES (DTC)
DATA:
AIRFLOW
CALCULATED LOAD
COOLANT TEMPERATURE
ENGINE RPM
IGNITION ADVANCE
INJECTOR DURATION
LONG TERM FUEL TRIM
OXYGEN SENSOR(S) PARAMETERS
SHORT TERM FUEL TRIM
THROTTLE POSITION
VEHICLE SPEED
INSPECTION & MAINTENANCE
(I/M) READINESS
Y
N
are a code that can be cross-referenced
against a table that describes it. Better
scan tools will show both the DTC
value and its definition.
DTCs are not all that can be shown
by the scan tool. OBDII specifications
include up to 10 modes of operation.
However, not all scan tools provide for
all of these and not all vehicles provide
for all modes.
Apart from the Diagnostic Trouble
Codes, the other modes listed in the
OBDII standard include showing
ON-BOARD MONITORING
VEHICLE INFORMATION
pending DTCs, clearing DTCs, showing a list of DTCs cleared previously,
showing current (real-time) data,
showing freeze frame data (data captured at the time of a DTC), test results
for emissions components, control
operation of on-board components and
vehicle information. Manufacturers
may also include additional modes.
Not all DTCs are necessarily supported or required by a particular
vehicle model. Also some codes are
manufacturer-specific rather than
Diagnostic trouble codes
The scan tool shows the details of
any malfunctions. These are shown as
Diagnostic Trouble Codes (DTCs) and
siliconchip.com.au
The OBD indicator light (or engine light) appears on the dashboard display of a
modern car when the ignition is first turned on. If everything is OK, it goes out a
few seconds after the engine is started.
February 2010 11
A Look At Engine Control Systems
The Engine Control Unit (ECU),
as the name implies, controls the
engine and it does this to provide
optimum performance under all
conditions. Its job is to also ensure
that the exhaust emissions are as low
as possible and in order for this to
happen the ECU monitors various
sensors. The ECU has control over
fuel delivery, ignition timing and
exhaust gas recirculation to meet
these requirements.
Fuel is delivered to the engine using injectors that open for a certain
period to meter the quantity. The
ECU calculates the amount of fuel
to deliver to the engine, based on
various sensors. These include the
volume of the air intake using a Mass
Air Flow (MAF) meter or indirectly
via a Manifold Absolute Pressure
(MAP) sensor, the air temperature
and RPM data.
Other sensors include fuel pressure and air temperature sensors,
oxygen sensors to measure oxygen
levels in the exhaust system, a tach
ometer sensor for engine RPM, a
throttle position sensor (TPS) and
coolant and oil temperature sensors.
For ignition timing calculations,
the ECU monitors engine position,
engine RPM, engine load and engine
temperature. It also checks for engine knocking using a knock sensor.
Exhaust Gas Recirculation (EGR)
valve control is based on engine
temperature, engine load and the
required emissions. It is a system
that recycles some of the exhaust gas
back into the engine inlet in order
to reduce nitrous oxide emissions.
The engine can be run in closedloop or open-loop mode. In openloop operation, the ECU uses a predefined table of values for ignition
timing and injector duty cycle versus
engine RPM, air intake mass and
engine temperature. When running
open-loop, the fuel mixture will generally be rich, with the engine using
more fuel than can be fully burnt in
the combustion process.
Open-loop operation generally
only occurs when the engine is under heavy load, such as when the
vehicle is accelerating.
Under normal cruise and light
throttle conditions, the engine
normally runs in closed-loop mode
whereby the fuel delivery is adjusted
so as to maintain required air/fuel
mixtures.
In general, air/fuel ratios are maintained at “stoichiometric” where
there is just sufficient oxygen for the
fuel to be completely burnt.
Under stoichiometric conditions,
the catalytic converter can work best
at converting combustion by-prod-
ucts to less harmful compounds.
Carbon monoxide (CO) is converted
to carbon dioxide (CO2), unburnt hydrocarbons to carbon dioxide (CO2)
and water (H2O), and nitrous oxide
(NO) to nitrogen (N2). Many cars also
include a diagnostic oxygen sensor
that is mounted after the catalytic
converter to check efficiency.
Another benefit of the oxygen
sensor is that the ECU can learn to
predict the amount of fuel to provide under differing conditions. So
the ECU compares the predefined
table of values for injector duty
cycle against the actual duty cycle
required to satisfy the required mixture, as gauged by the oxygen sensor
signal. The ECU then sets up a table
of trim values based on this feedback
from the oxygen sensor.
It can take some time for the ECU
to learn the values and provide a full
map of trim values. For this, it will
require the engine to be run under a
variety of conditions. These trim values are called “long-term fuel trim”.
The ECU provides these trim
values to allow the engine to run
more efficiently. While driving, the
engine RPM and load can change
rather quickly and the oxygen sensor is not fast enough to respond
to these changes. As a result, the
mixture feedback to the ECU is not
generic. Vehicle manufacturers may
use manufacturer-specific DTC codes
and imported vehicles may also use
DTC codes different from generic DTC
codes. We recommend that you do
not fully rely on the DTC, especially
for pre-2006 vehicles unless you can
confirm that the generic DTC codes
apply to your vehicle.
(6) P0500-P0599: Vehicle Speed Controls and Idle Control System.
(7) P0600-P0699: Computer Output
Circuit.
(8) P0700-P0899: Transmission.
The full list of power train DTCs
is far too long to feature here. You
can find it at www.obd-codes.com/
trouble_codes/
Body codes include those for seat
belts, lamps, solenoids, motors, ECU
failure, climate control, air bags, central locking, doors, external mirrors
etc. The list is at: www.obd-codes.
com/trouble_codes/obd-ii-b-bodycodes.php
Chassis codes include those for
anti-skid braking (ABS) and traction
control. For the full list see: www.
obd-codes.com/trouble_codes/obd-iic-chassis-codes.php
Fig.2: the OBD indicator symbol looks
like a car engine. It illuminates if
there is an engine malfunction.
12 Silicon Chip
DTC categories
DTCs are divided into four categories: “P” codes for the power train,
“B” codes for body, “C” for chassis
and “U” for network. P codes are the
most common and include engine
sensor malfunctions. These are further
categorised into eight sub-sections:
(1) P0010-P0099: Fuel and Air Metering and Auxiliary Emission Controls.
(2) P0100-P0199: Fuel and Air Metering.
(3) P0200-P0299: Fuel and Air Metering (Injector Circuit).
(4) P0300-P0399: Ignition System or
Misfire.
(5) P0400-P0499: Auxiliary Emissions
Controls
siliconchip.com.au
Table 1: List Of Toyota Car Teaching Manuals
fast enough for rapidly changing
conditions.
However, using trim values based
on past driving will have the engine
run at close to the desired mixtures
without waiting for the oxygen sensor response. When the oxygen sensor does respond, the ECU uses this
information to make a short-term
fuel trim adjustment to the current
injector duty cycle. Ultimately, these
short term trims are used to make up
the long term fuel trim map.
For more detail on fuel trim, refer
to http://www.autoshop101.com/
forms/h44.pdf
As mentioned above, in order to
understand some of the data available from a scan tool, it is important
to understand how the engine works.
An understanding of car electronics
is also required.
The following links to teaching
manuals will help. The USA branch
of Toyota supplies them but most
of the information is general and
applies to any vehicle.
The links are grouped into separate sections and a very good coverage is made of knock, oxygen,
speed, pressure, MAF, position and
temperature sensors in the sensors
section.
To access these, use the link
http://www.autoshop101.com/forms/
hX.pdf but replace the “X” with one
of the “h numbers” listed for each
category. So, for example, replace
Network codes are associated with
communication between separate
control modules within the vehicle or
between the scan tool and the OBDII
connection. For the list of these see:
www.obd-codes.com/trouble_codes/
obd-ii-u-network-codes.php
Many very basic scan tools will
show trouble codes purely as the
DTC value. For example, the display
may show a DTC as P0130. This value
would then have to be looked up to
reveal the code definition. However,
it is far easier to use a scan tool that
also includes the DTC definition. So,
for example, a scan tool that shows
“P0130 Oxygen Sensor Circuit Malfunction (Bank 1 Sensor 1)” is easier
to use than one that just shows the
DTC value.
A scan tool should also provide the
siliconchip.com.au
H1-H8: Basic Electronics
http://www.autoshop101.com/forms/h1.pdf
http://www.autoshop101.com/forms/h2.pdf
http://www.autoshop101.com/forms/h3.pdf
http://www.autoshop101.com/forms/h4.pdf
http://www.autoshop101.com/forms/h5.pdf
http://www.autoshop101.com/forms/h6.pdf
http://www.autoshop101.com/forms/h7.pdf
http://www.autoshop101.com/forms/h8.pdf
H12-H18: Advanced Electronics
http://www.autoshop101.com/forms/h12.pdf
http://www.autoshop101.com/forms/h13.pdf
http://www.autoshop101.com/forms/h14.pdf
http://www.autoshop101.com/forms/h15.pdf
http://www.autoshop101.com/forms/h16.pdf
http://www.autoshop101.com/forms/h17.pdf
http://www.autoshop101.com/forms/h18.pdf
H20-H27: Electronic Fuel
Injection
http://www.autoshop101.com/forms/h20.pdf
http://www.autoshop101.com/forms/h21.pdf
http://www.autoshop101.com/forms/h22.pdf
http://www.autoshop101.com/forms/h23.pdf
http://www.autoshop101.com/forms/h24.pdf
http://www.autoshop101.com/forms/h25.pdf
http://www.autoshop101.com/forms/h26.pdf
http://www.autoshop101.com/forms/h27.pdf
H31-H38: Sensors
http://www.autoshop101.com/forms/h31.pdf
http://www.autoshop101.com/forms/h32.pdf
http://www.autoshop101.com/forms/h33.pdf
http://www.autoshop101.com/forms/h34.pdf
http://www.autoshop101.com/forms/h35.pdf
http://www.autoshop101.com/forms/h36.pdf
http://www.autoshop101.com/forms/h37.pdf
http://www.autoshop101.com/forms/h38.pdf
H39-H41: Ignition
http://www.autoshop101.com/forms/h39.pdf
http://www.autoshop101.com/forms/h40.pdf
http://www.autoshop101.com/forms/h41.pdf
H42-H44: Fuel
http://www.autoshop101.com/forms/h42.pdf
http://www.autoshop101.com/forms/h43.pdf
http://www.autoshop101.com/forms/h44.pdf
H46-H48: OBD
http://www.autoshop101.com/forms/h46.pdf
http://www.autoshop101.com/forms/h47.pdf
http://www.autoshop101.com/forms/h48.pdf
X with a number from 1-8 for one
of the eight Basic Electronics manuals. For the first manual, the link
is http://www.autoshop101.com/
forms/h1.pdf and so on:
h1-h8: Basic Electronics
h12-h18: Advanced Electronics
h20-h27: Electronic Fuel Injection
h31-h38: Sensors
h39-h41: Ignition
h42-h44: Fuel
h46-h48: OBD
Table 1 above shows the full list
of the teaching documents available.
means to clear the DTC. Clearing the
code removes the trouble code from
the ECU and switches off the MIL.
Another way to remove DTCs is to
disconnect the vehicle battery for a few
seconds, to clear the ECU memory. But
if a trouble code is cleared in this way,
the car’s audio systems will require its
security code to be re-entered and the
radio station presets reprogrammed.
The ECU may also lose its fuel trim
values (see section headed Engine
Control Systems).
Note that a trouble code will reappear if the fault that caused the DTC
has not been fixed.
Scan tools can usually show pending emission-related DTC codes. These
are problems that the ECU has detected
recently during the current or last
completed driving cycle. They may
be cleared it the ECU finds that the
problem has not recurred or a pending
DTC may be transferred to become a
DTC. Pending DTCs are useful as an
indicator for revealing if a trouble code
is likely to reappear, indicating that a
fault has not been fixed.
Parameter data
Apart from DTCs, being able to access parameter data is a vital aspect
for locating problems. If your scan tool
does not provide for this diagnostic
data then you are limited in how faults
can be diagnosed. Diagnostic data includes real-time data, freeze frame data
and emissions tests. Diagnostic data is
addressed as a Parameter IDentification (PID) value. The PID listing can
be found at http://en.wikipedia.org/
wiki/OBD-II_PIDs
February 2010 13
The OBDII Data Link Connector
The OBDII Data Link Connector is
shown at right. It has 16 pin locations for
contacts but only a few of these will be
used, depending on the communication
protocol standard used by the vehicle to
send data to the OBDII scan tool.
At present, there are five protocol standards. Since 2008, all new US vehicles are
required to use only the Controller Area
Network (CAN) protocol for OBDII communication and this standard is eventually
likely to be adopted worldwide.
In Australia, any one of these five protocols may be used:
(1) CAN (Controller Area Network).
(2) ISO (International Organisation for
Standardisation) 9141-2.
(3) ISO 14230 KWP2000 (Keyword Pro
tocol).
(4) SAE (Society of Automotive Engineers)
J1850 PWM (Pulse Width Modulation).
Some of the values that can be displayed in real time include airflow rate
from a Mass Air Flow (MAF) sensor,
absolute throttle position, calculated
engine load, coolant temperature,
RPM, fuel pressure, ignition timing,
inlet manifold pressure, fuel trims,
oxygen sensor voltages, vehicle speed,
ambient air temperature and air/
fuel ratio. The data is continuously
updated so any output changes from
each sensor can be viewed.
For some scan tools, you would have
to enter the PID value and then wait for
the response from the ECU to show the
requested data. This can be in hexadecimal format and in a raw form that
requires a formula to calculate a result.
Some scan tools do this work for you
and show all available data from the
ECU and include the PID definitions.
The data is also calculated to show the
value with units such as Volts, %, °C
etc, making the tool far easier to use.
14 Silicon Chip
(5) SAE J1850 VPW (Variable Pulse Width).
While CAN is becoming the preferred
protocol from 2008, typically the ISO
protocol is used by European and Asian
cars and some Dodge, Chrysler, Jeep,
Ford and General Motors vehicles. VPW
is also used for General Motors, Dodge,
Chrysler, Jeep, Toyota and Isuzu vehicles.
Ford uses PWM.
More details on these protocols is
available at: http://en.wikipedia.org/wiki/
On-board_diagnostics
Fortunately, what protocol a vehicle
uses is not important because most handheld scan tools will automatically work with
any of them.
For OBDII compatibility, your vehicle
needs to have one of the following pin sets:
(1) CAN protocol – uses pins 5, 6, 14 & 16.
(2) ISO and KWP protocol – uses pins 5,
7, 15 (optional) & 16.
Freeze frame data is the information captured by the ECU concerning
the Diagnostic Trouble Code (DTC).
The information shows what data the
sensors were providing at the time the
DTC occurred.
Emissions testing
Another worthwhile feature of the
OBDII standard is emissions testing or
what is called “Inspection and Maintenance (I/M) Readiness”. These tests
will reveal if the vehicle meets the
emissions standards required when
the vehicle was manufactured. The
tests include monitoring of engine
misfiring, fuel systems and comprehensive components (such as evaporative emission controls). These tests are
made continuously.
In addition, non-continuous I/M
readiness emissions monitoring are
made for the Exhaust Gas Recirculation (EGR) system, oxygen sensors,
1
8
9
16
OBDII DATA
LINK CONNECTOR
OBDII DATA LINK CONNECTOR PIN DEFINITIONS
DEFINITION
PIN
1
2
3
4
5
6
7
8
9
10
11
12
13
Manufacturer's discretion
Bus(+) SAE J1850 PWM & DAE 1859 VPW
14
15
CAN low SAE J2284 & ISO 15765-4
L line of ISO 9141-2 & ISO 14230-4
Battery positive
16
Manufacturer's discretion
Chassis Ground
Signal Ground
CAN high ISO 15765-4 & SAE J2284
K line of ISO 9141-2 & ISO 14230-4
Manufacturer's discretion
Manufacturer's discretion
Bus(–) SAE J1850 PWM only
Manufacturer's discretion
Manufacturer's discretion
Manufacturer's discretion
(3) VWP protocol – uses pins 2, 5 & 16.
(4) PWM protocol – uses pins 2, 5, 10
& 16.
catalytic converter, oxygen sensor
heater, secondary air, heated catalyst
and the air-conditioning system. These
monitors are tested during specific
drive cycles where the full extent of
the sensors’ operation can be checked.
Testing of these will indicate a “Not
Ready” status if testing is not yet
complete.
On-board monitoring of sensors is
also available. These provide a minimum value, a maximum value and a
current value for each non-continuous
monitor.
Oxygen sensors, for example, are
characterised by Rich-to-Lean O2 sensor threshold voltage, Lean-to-Rich O2
sensor threshold voltage, Low sensor
voltage threshold for switch time
measurement, High sensor voltage
threshold for switch time measurement, Rich-to-Lean switch time in
ms, Lean-to-Rich switch time in ms,
Minimum voltage for test, Maximum
siliconchip.com.au
voltage for test, and Time between
voltage transitions in milliseconds.
Multiple oxygen sensors
OBDII-compliant vehicles will have
at least two oxygen sensors. There will
be one to monitor the air/fuel mixture
at the exhaust manifold (the control
sensor) and another to monitor gasses
following the catalytic converter (the
diagnostic sensor). The latter allows
catalytic converter’s performance to
be checked.
Some engines will have more oxygen sensors, depending on how the
exhaust manifolds are arranged. V6
and V8 engines will have separate
control oxygen sensors for each side
of the engine. Whether such an engine
then has one or two diagnostic sensors
depends on whether the exhaust is fed
into one catalytic converter or two.
Oxygen sensors are listed according
to their number and bank. Sensor 1
is associated with the cylinder 1 side
of the engine, while Sensor 2 would
also be used in a V6 or V8 engine (ie,
another sensor in the second exhaust
manifold). Bank number refers to the
sensor usage. Bank 1 is the control
sensor that measures air/fuel ratio at
the exhaust manifold. A bank 2 sensor would be a diagnostic sensor that
mounts after the catalytic converter.
Vehicle information can also be displayed using a scan tool. This shows
Vehicle Identification Numbers (VIN),
Calibration Identification Number
(CIN) and Calibration Verification
Numbers (CVN).
Using a scan tool
One point that needs to be made
regarding scan tools is that the OBDII
features available for that vehicle will
limit what can be done with a scan
tool. So a scan tool may be capable of
showing freeze frame data but it will
not be able to display it if the vehicle
does not provide the feature.
While OBDII information appears
to be complicated, when it comes to
actually using a scan tool it is quite
easy, especially with a good scan tool.
Basically, you just plug in the lead to
the OBDII data link connector located
in the vehicle, switch on the ignition
and wait for the scan tool to communicate with the ECU. You then select
the functions you want to use, such
as viewing DTCs, clearing DTCs and
viewing data.
The handbook supplied with the
siliconchip.com.au
Making Your Own Scan Tool
There is a lot of information available about building your own OBDII scan tool using
the ELM series of integrated circuits (ICs) to decode the OBDII protocol into a form
suitable for a laptop computer. Although this is not an exhaustive list, here are some
websites that may be of use in finding the data and applications for the ELM ICs and
for software to run with them on the computer.
(1) The ELM series of ICs has data at http://www.elmelectronics.com/obdic.html
(2) For software, see http://www.obd2crazy.com/software.html, while commercial
software is at http://www.obd-ii.de/screensm2.html
An OBDII project is available at: http://courses.cit.cornell.edu/ee476/FinalProjects/
s2009/ama64_maa66/ama64_maa66/index.html
(3) ALDL (Assembly Line Diagnostic Link) Interface: for Holden VR, VS and VT Commodores that use the ALDL interface see http://www.techedge.com.au/vehicle/
aldl8192/8192hw.htm For VN, VP and JE Camira see http://www.techedge.com.au/
vehicle/aldl160/vn_aldl.htm
Note: a build-it-yourself OBDII scan tool interpreter using one of the ELM ICs is
featured in this issue of SILICON CHIP.
Is OBDII Available On My Car?
Vehicles built in Australia before January 2006 do not usually have functioning
OBDII. The Holden VR, VS & VT Commodores used a different system to OBD called
Assembly Line Diagnostic Link (ALDL) standard. Details about this can be found in
the “Making Your Own Scan Tool” panel – see above.
AU and BA Falcons and VY & VX Commodores had the OBDII connector and some
OBDII functions. The BA Falcon and VY Commodore did not include DTCs but included
live engine data.
The BF Falcon and the VZ Commodore do have full OBDII compliance. The FG Falcon
and VE Commodore have a huge range of data available. Also, the locally built Toyota
Avalon included OBDII compliance.
Imported vehicles sold before January 2006 cars may have OBDII. US-built cars
such as Chrysler, built from around 1996 onwards, do have OBDII compliance. European cars from about 2000 will also have OBDII while Subarus had OBDII from 2002.
Other pre-2006 vehicles may have an OBDII-style connector or an alternative OBD
connector. These tend to operate using a proprietary OBD system that is specific to
either the vehicle’s manufacturer or to the model. Scan tools are generally available
for use with these vehicles either from the manufacturer or a scan tool supplier. For
example scan tools are available for 1990 and onward VW and Audi at www.theobd2shop.com.au. These are called VAG (or Volkswagon AG) readers.
An extensive (but not exhaustive) check-list of pre-2006 OBDII compatible vehicles in
Australia is available at www.scangauge.com.au/support/CompatibleVehicles.shtml
scan tool will show how it is used.
If you want to gain some experience
with a scan tool, you could force a
trouble code by unplugging a sensor’s
connecting lead while the ignition is
off. An easy sensor to locate is the
Mass Air Flow (MAF) sensor, located
between the air filter and the inlet
manifold. A MAF sensor is used on
many cars although others may have
a Manifold Absolute Pressure (MAP)
sensor instead.
With the MAF sensor disconnected
and after starting the engine, an almost
immediate pending DTC should appear and will be shown when pending
codes are accessed on the scan tool.
A look at real-time data for the MAF
sensor will show a zero reading. If you
now switch off the engine and restart,
the Malfunction Indicator Lamp will
probably light and a DTC may be set.
Finally, switch off the engine, reattach the MAF sensor and start the
engine again. The DTC may automatically clear or you may need to clear it
with the scan tool. A look at the MAF
live data should now show readings
February 2010 15
The Autel MaxScan GS500 Scan Tool
L
et’s take a look here at the Autel MaxS-
can GS500. This is a hand-held unit that
weighs in at 300g and measures 95 x 180
x 35mm. A 54 x 35mm backlit LCD shows
the information, while four pushbuttons
provide the numerous functions.
On the top of the unit is a DB15F connector which is connected to the OBDII
connector on the vehicle via a 1.4m OBDII
to serial cable. A separate serial-to-USB
cable is provided for upgrading the inter-
This view shows the OBDII connector fitted to a 2005 Honda Accord.
It’s mounted under the dashboard,
near the driver’s side kick panel.
The same type of connector is fitted
to other late-model cars.
above zero that will rise in g/s (grams
per second of air mass) as more throttle is applied.
In order to get the best from your
scan tool, a comprehensive understanding of how a modern vehicle
engine operates is required. Included
here is some engine control information located in the panel headed “A
Look At Engine Control Systems”.
We have also provided some useful
tips on fault diagnosis in the following section.
Diagnosis using a scan tool
An OBDII scan tool should only be
used as an aid to assist in diagnosis of
a fault condition. When a Diagnostic
Trouble Code (DTC) is found, it only
indicates where the ECU has found a
problem but not the cause. In other
words, the ECU indicates the effect
of the problem rather than where the
problem may be.
As an example, a fault code for a
16 Silicon Chip
nal DTC definitions library via a computer
connected to the internet.
A padded black Nylon carry-case is
also supplied to protect the OBDII scanner, its operating manual and the leads. A
CD is also included, providing a library of
over 8000 DTC definitions. The CD also
includes a USB driver and a manual for
the GS500, as well as manuals for other
Autel scanners.
The GS500 works with all OBDIIcompliant vehicles and supports CAN and
all other OBDII communication protocols
such as ISO 9141-2, ISO 14230 KWP2000,
SAE J1850 PWM and SAE J1850 VPW.
Power comes via the OBDII connector.
There are no internal batteries and it will
not power up without connection to the
OBDII port or the USB port. This is typical
of scan tools.
The list of GS500 functions is numerous. These are:
(1) Read and clear generic OBDII diagnostic trouble codes, including pending
trouble codes.
(2) Read and clear manufacturer-specific
trouble codes, including those for GM,
Ford, Chrysler, Toyota and many more.
(3) Turn off the Malfunction Indicator
Lamp (MIL).
(4) Show Freeze Frame data.
(5) Display Monitor and I/M readiness
status.
(6) Read live data streams.
(7) Display oxygen sensor test data.
(8) Perform Modules Present test.
(9) Retrieve Vehicle Information (VIN, CIN
and CVN).
The GS500 includes real time (live)
data display. This is an invaluable aid to
diagnosing the cause of trouble codes. In
addition, the internal trouble code definitions library is an excellent inclusion so
that Diagnostic Trouble Codes are shown
alongside their definition. This saves looking up a long list of trouble codes versus
their definitions.
For live data, the Parameter IDentification (PID) values are shown by their definition rather than the PID number and the
data is shown with units. That means that
the scan tool is easy to use. Any data that
cannot all be shown on the screen at the
same time can be accessed by scrolling to
the next screen. Alternatively, there is the
option to customise what data is shown.
Operation of the scan tool to access
information involves a simple 2-button up
or down scroll through a menu system. An
extra two buttons are used to acknowledge
or exit (using Y or N buttons). Having
just four buttons makes the GS500 easy
MAF sensor (DTC #P0100) or MAP
sensor (DTC #P0105) could just mean
that there is no power to the sensor.
This may be due to loss of either the
ground or positive supply rail (or
both) and the sensor itself may not be
at fault. With this fault, probing the
sensor leads with a multimeter should
be done to check for power to the sensor. Continuity from the 0V supply to
ground (chassis) should also be tested.
Another example is for an oxygen
sensor DTC. This DTC may show as
P0130 [Oxygen sensor circuit mal
function (Bank 1 Sensor 1)]. It refers
to an incorrect control oxygen sensor
output for a narrowband sensor.
Note that wideband sensors (as used
on some late model vehicles) have
a different set of Diagnostic Trouble
Codes. Their output response is very
different to the narrowband sensors.
The P0130 fault code means that the
ECU has found that this sensor is not
providing the expected output. It does
not necessarily mean that the oxygen
sensor is at fault and you may need to
look elsewhere to locate the cause. A
rash approach would be to purchase
a replacement sensor only to find that
this does not clear the fault.
To trace where the fault is, use the
scan tool to read freeze frame data or
the data stream. Freeze frame shows
what the parameters were at the time
the DTC occurred but this feature may
not be available in your scan tool or
from the OBDII in your vehicle. Real
time data can show the current sensor readings but make sure you use a
scan tool that can show real time data.
It’s a matter of setting the scan tool to
monitor the oxygen sensor readings
and viewing the sensor readings.
The correct output from a Zirconiabased narrowband sensor when the
engine is idling is where the voltage
cycles above and below a nominal
450mV. If the voltage stays well above
this voltage (say >800mV), then the
siliconchip.com.au
The Autel
MaxScan GS500
Scan Tool comes
with a black
carry case, a CD
with over 8000
DTC definitions,
a manual and
connecting cables.
The GS500 works with all OBDIIcompliant vehicles and has a long
list of features. Power comes from the
OBDII connector.
to drive and it should prove invaluable in
diagnosing vehicle engine malfunctions.
The Autel MaxScan GS500 hand-held
OBDII scanner can be purchased from
Engine Code Readers Australia – www.
theobd2shop.com.au
Alternative hand-held scan tools are
also available from automotive suppliers
such as Repco. Check that the scanner’s
features suit your application. See also
www.scangauge.com.au/index.html and
www.jaycar.com.au
mixture is rich and if the voltage stays
well below (say <100mV), then the
mixture is lean. These voltages are for
a sensor that is in working condition.
If the voltage remains low, it could
be that there is an air leak to the inlet
manifold between the MAF sensor and
inlet manifold. This leak will cause
the mixture to be leaner than normal
because the MAF is not measuring all
the air entering the engine. In other
words, the air leak is providing extra
unmetered air that the ECU does not
know about. A split in the crankcase
ventilation hosing is a likely cause.
Another cause for an oxygen sensor
DTC is an air leak in the exhaust manifold or oxygen sensor gasket, causing
a lean reading.
If there don’t appear to be any air
leaks, then check the sensor’s operation when it is removed from the
engine. You will need to determine
which leads are for the oxygen sensor
element and which leads are for the
heater and this can be found by referring to the vehicle’s wiring diagram.
Measuring the output voltage of
the sensor when under the flame of
a butane blowtorch can test a narrowband sensor. Heat the tip of the
sensor under the flame until it has a
red glow. The output voltage should
rise to >800mV due to the rich mixture
and drop to <100mV when the sensor
is removed from the flame. The sensor
may be faulty if it does not produce
any voltage.
Another scenario for the fault code
may be that the sensor voltage stays at
a fixed voltage. It is fairly normal for
the bank 2 oxygen sensor (located at
the output of the catalytic converter)
to show a relatively fixed voltage of
about 450mV. But a fixed voltage is not
normal for a control oxygen sensor at
the exhaust manifold.
Yet another possibility is that the
sensor’s output voltage (as measured
using an oscilloscope or multimeter)
always shows a rich (>700mV) reading. For a sensor with only one signal
lead, the reading would be taken between the sensor signal and the body
of the sensor. The >700mV reading
would suggest that the sensor is OK.
Instead, the fault in this case may be
that the negative (-) sensor terminal or
the sensor body for the single output
lead sensor is not grounded correctly.
This could be due to a wiring fault
or a broken connection inside the ECU.
Either way, grounding the negative (-)
sensor terminal to chassis can restore
sensor operation. An alternative solution would be to find the negative (-)
sensor wiring for the second oxygen
sensor used in the vehicle and connect
the floating negative sensor terminal
to that.
With a single-wire sensor, the sensor may be isolated from chassis due
to corrosion on the sensor or a faulty
earthing strap connection from the
SC
engine to chassis.
siliconchip.com.au
February 2010 17
|