Points to Note When Diagnosing Faults
POINTS TO NOTE WHEN DIAGNOSING FAULTS
Important
Diagnostic trouble codes should be used for diagnostic purposes only. It is by no means certain that they indicate a defective component.
It is impossible to give any general rules for the procedure to follow when diagnosing faults in each individual case. Depending on the fault symptoms and other information available, one method may be the best in some situations and another method the best in others.
However, the following points may serve as guidance when diagnosing faults in the Trionic system.
1. Always begin fault diagnosis by using the Scan Tool to obtain readouts of any diagnostic trouble codes stored in the control module. Use the "ALL SYSTEMS" command to obtain readouts of all trouble codes. Make a note of the trouble codes or save them in the Scan Tool's memory with the "SAVE FAULT CODES" command.
Readouts of internally stored codes can be obtained with the "RECALL FAULT CODES" command.
Fault codes present:
Continue with "Fault diagnosis using diagnostic trouble codes".
No fault codes present:
Continue with "Fault diagnosis based on fault symptoms" or "Fault diagnosis, components".
2. Some fault diagnosis procedures may entail the unplugging of connectors while the ignition switch is in the ON position. This can give rise to the generation of trouble codes. For this reason, on completion of fault diagnosis procedure, always clear any diagnostic trouble codes that may have been generated. Clear all diagnostic trouble codes by using the "CLEAR" command.
3. Check fuses 14, 23 and 28.
4. Inspect connectors for corrosion on pins and contact surfaces, excessive play, loose or dislodged pins and/or sleeves, or anything else which may be the cause of poor contact or a deterioration in conductivity. If poor contact is suspected, always use KONTAKT 61 (part No.45-30 04 520) contact cleaner on the female connector.
NOTE: Contact cleaner and/or grease must not used on the oxygen sensor connectors.
5. Check to see whether the CHECK ENGINE lamp (MIL) or other warning lamp is on.
6. Faults may be either permanent or intermittent.
The criteria of a permanent fault are continuously fulfilled, i.e. the fault is constantly present.
The criteria of an intermittent fault are occasionally fulfilled, i.e. the fault is present under certain conditions only. Such conditions may be:
- Faulty connectors or switches (see point 4).
- Electromagnetic interference. Such interference may be caused by the car's own equipment or by an external source when the car passes centers of powerful electromagnetic radiation such as airports, radio and TV masts, and high-tension cables.
- Defective components. The operation of relays, solenoids, etc. may cause interference by producing sparks when making or breaking contact.
Intermittent faults call for careful and accurate analysis to avoid the replacement of faultless components.
7. General rules:
- Connection of a BOB should be carried out with the ignition switch in the OFF position.
- The ignition switch must be in the OFF position when switches are turned off.
- Measurement of resistance should be carried out with the ignition switch in the OFF position.
8. Measuring the resistance of valves and relays.
Nominal resistance is specified at 2O°C (68°F). The resistance of windings is strongly temperature~dependent and increases with rising temperature.
Exercise care when judging the results of such resistance measurement.
9. The strategy of fault diagnosis, with or without the use of diagnostic trouble codes, is based on only one fault, a primary fault, occurring. However, a primary fault can generate other faults, consequential faults. When the primary fault is rectified, the symptoms of the consequential faults disappear at the same time.
The probability of two independent faults occurring at the same time is judged to be small and therefore not covered in this manual.
10. When suitable remedial action has been taken, always end fault diagnosis performed with or without the use of diagnostic trouble codes, by making sure that the trouble code or fault symptom is no longer present.