GM Service Manual Online
For 1990-2009 cars only

Important Preliminary Checks Before Starting

Before using this section, perform Diagnostic System Check - Engine Controls to verify the following items:

    â€¢ The powertrain control module (PCM) and malfunction indicator lamp (MIL) (Service Engine Soon) are operating correctly.
    â€¢ There are no DTCs stored.
    â€¢ Ensure that the engine coolant temperature (ECT) is not above 130°C (266°F). This will cause the PCM to operate in the Engine Metal Overtemp Mode. While in this state, the PCM will turn OFF four cylinders at a time to prevent the engine coolant temperature from reaching damaging levels. Engine Metal Overtemp can be perceived as a lack of power, engine miss, or rough idle. If the engine is operating in the Engine Metal Overtemp mode, refer to DTC P1258.
    â€¢ Scan tool data is within the normal operating range. Refer to Scan Tool Data List .
    â€¢ Verify the customers complaint to reference the correct symptom table.

Visual/Physical Check

Several of the symptom procedures call for a careful Visual/physical check. This check can lead to correcting a problem without further checks and can save valuable time. This check includes the following items:

    â€¢ PCM grounds for being clean, tight, and in the proper location.
    â€¢ Vacuum hoses for splits, kinks, proper routing, and connections. Refer to the Vehicle Emission Control Information label. Check thoroughly for any type of leak or restriction.
    â€¢ Intake air system for the following conditions:
       - Dirty or damaged air cleaner element or housing
       - Damaged or collapsed intake air ducts.
       - Poor intake air system connections
    â€¢ Air leaks at the throttle body and/or intake manifold.
    â€¢ Throttle body contaminants or deposits.
    â€¢ Accelerator cable binding or damage.
    â€¢ Ignition system wiring for incorrect routing and/or poor connections.
    â€¢ System wiring for routing near high frequency devices (electromagnetic interference (EMI) condition).
    â€¢ Engine cooling system leaks. Refer to Loss of Coolant in Engine Cooling.

The following Symptom tables are located in this section:

    â€¢  Hard Start
    â€¢  Surges/Chuggles
    â€¢  Lack of Power, Sluggishness, or Sponginess
    â€¢  Detonation/Spark Knock
    â€¢  Hesitation, Sag, Stumble
    â€¢  Cuts Out, Misses
    â€¢  Poor Fuel Economy
    â€¢  Poor Fuel Fill Quality
    â€¢  Rough, Unstable, or Incorrect Idle and Stalling
    â€¢  Dieseling, Run-On
    â€¢  Backfire
    â€¢  Restricted Exhaust in Engine Exhaust