Introduction

PRELIMINARY PROCEDURES
^ Before using this section you should have performed the "On-Board Diagnostic Procedures" (see ON BOARD DIAGNOSTICS) which verifies that the electronic control unit and "CHECK ENGINE" light are operational, as well as no trouble codes were stored.

^ Always use the FLOW OF DIAGNOSIS for proper testing sequence.

^ Several of the following symptom procedures call for a careful visual/physical check. This step is very important - it can lead to correcting a problem without further checks and can save valuable time.

^ Certain basic faults can be undetectable by the self-diagnostic system of the electronic control unit and in some cases can actually interfere with the self-checking and fault memory operation.

^ Low battery voltage, for example, can cause erroneous faults to set in control unit fault memories or can cause a system to go "Fail Safe" without setting a fault in memory. On the other hand, system fault memories are cleared whenever the control unit or the battery is disconnected. Therefore, all fault memories should be read prior to any vehicle power interruption or troubleshooting.

CHECK THE FOLLOWING:
NOTE: It is essential that the vehicle has been properly warmed up and is at operating temperature, except when attempting to diagnose a cold driveability problem. The catalytic converter and the oxygen sensor will not function as designed if this is not achieved. Failure to do so will result in inaccurate test results.

COMPLAINT VERIFICATION
Whenever possible the repairing technician should personally verify the complaint. Having experienced the malfunction, the technician is less likely to try to repair non-existent faults.

MALFUNCTION VERIFICATION
Today's sophisticated automotive systems are easily misunderstood, which can lead to repairs that attempt to force a particular system to perform in a way that it was never intended to operate. Therefore, the troubleshooting technician should compare the system operation to the nominal system operation as described in the section DESCRIPTION AND OPERATION. Furthermore, the technician is also encouraged to compare the problem vehicle system operation with a known good vehicle.

PREVIOUS REPAIRS
The vehicle repair history can provide explanations to unusual complaints which seem to elude normal troubleshooting attempts. Incorrect components or unapproved repairs can have subtle influences on seemingly unrelated systems.