Using the ISAT
Fault diagnosis, LH 2.4 and LH 2.4.2Additional fault codes and command codes
On model year 1991 and later cars, the LH 2.4 and LH 2.4.2 fuel injection Systems incorporate a number of additional fault codes that can be retrieved by means of an ISAT.
There are also more command codes, so that the number of usable codes now amounts to more than 20.
Like the table of command codes, the fault code table contains all the codes but those that have been added for model year 1991 are specially marked. All fault codes beginning with 4 or 5 are permanent faults while those beginning with 2 or 3 indicate that the fault is of an occasional or intermittent nature.
Fault diagnosis using the ISAT
Before starting fault diagnosis
Apart from a thorough knowledge of the system, successful fault diagnosis on the LH system also requires the use of an ISAT diagnostics instrument.
Since the LH system's integrated self-diagnosis function continuously monitors and records the majority of possible faults, both permanent and intermittent, it is extremely easy to use an ISAT to identify the fault, rectify it and afterwards check that the system is in perfect working order.
The system's integrated self-diagnosis functions, combined with the facilities provided by an ISAT, make for faster and above all more accurate fault diagnosis. The risk of replacing good components is reduced while service and repair costs can be kept down.
Is the fault in the LH system?
Sometimes the LH system is suspected of being faulty when the fault really lies in the engine or some other auxiliary system. For this reason, remember to check the following points before starting fault diagnosis on the system.
- battery condition
- engine condition
- charging system
- other auxiliary systems
- cable connections
- grounding points
- ignition system
Some important points to remember:
1 When carrying out fault diagnosis on microprocessor- controlled systems, memory sectors may be corrupted and give unusual symptoms. To erase all unusual symptoms, switch off the ignition for at least 35 seconds.
2 Read and make a note of all fault codes stored in the memory before disconnecting the battery or control module. Never disconnect the control module while the ignition is switched on as this will very likely ruin it.
3 When carrying out fault diagnosis on a car's electronic systems, always check first and foremost that the ground connections of the control module concerned are OK and that all supply voltages are correct. This is strongly recommended.
4 Always check the connector connections before starting fault diagnosis in other areas. Unplug the connectors and check that the pins are undamaged and secured with their barbs. Plug in the connectors again and clear all fault codes. Start the car and drive it to check whether the fault or faults persist.
5 On first being detected, every fault is assigned a fault code corresponding to a permanent fault. If the fault disappears, it will be assigned an intermittent fault code instead.
6 Since all signals round the 12 V level are proportional to battery voltage, the levels should only be used as guidance.
7 0 V signals denote ground but readings slightly above 0 V may be obtained on a sensitive multimeter.
8 Readings of the voltage on inputs and outputs must only be taken with the ignition switched on or with the engine running.
9 The black diagnostics socket is located under the rear seat on the RH side.
It is protected by a plastic cover.
10 The ignition switch should always be turned to the Drive position when carrying out diagnosis.
11 The LH system has been assigned system No. 1 in the ISAT.
12 If communication between the ISAT and the control module cannot be established, first check the wiring between pins 12 and 16 of the control module and the diagnostics socket (347). Also check that power and ground are present at the diagnostics socket and that the pins of the connector are undamaged.
13 When the contents of the system's fault memory have been transferred and stored in the ISAT, the actual diagnosis has been completed. The faults are now available in the form of five-digit codes, following which further fault diagnosis work can be continued in accordance with the fault-diagnosis chart for the system concerned.
Test readings on the control module connector
Before taking any test readings on the LH system, the contact strip in the control module connector must first be exposed. All test readings must subsequently be taken from the side where the leads are connected to the pins in the connector.
1 Remove the control module, located inside the car on the RH side between the wheel arch and the front door pillar.
2 Unplug the connector.
3 Remove the protective cover and the rubber dust excluder.
4 Withdraw the rubber gasket and lift up the contact strip.
5 Plug in the connector.
Checking the wiring
The words "Check the wiring between xx and yy" are used frequently in the fault-diagnosis charts.
Sometimes the wiring may run through different types of connector and, by implication, these must also be checked for circuit continuity and shorting. Also check by eye that leads and connectors, etc. are undamaged.
Be alert to the possibility of interference from components connected to, or adjacent to, the wiring concerned.
Breakout box
For taking test readings on the control module, primarily in the TC/ABS system, a breakout box is now available to facilitate fault diagnosis. This breakout box, which has part No.86 11 006, can of course also be used for diagnosing faults in the LH system.
ISAT command codes
When the ISAT is used for simulating signals or functions by sending command codes to the control module, the results will be shown on the display as a combination of numbers and letters (alphanumeric code)
The result is shown in the form of five characters.
Example 1:
To check the position of the throttle butterfly we enter command 201 on the ISAT keypad. With the engine running, the last five characters on the ISAT display should read BB1O1.
Example 2:
Sometimes we want to check whether a signal is high or low. To check the DRIVE signal we enter the command 203 on the ISAT keypad. If the signal is not activated, 8B000 will appear on the display to indicate that the signal is low.
If the signal is activated, it should be high and the ISAT display should show 8B103.