GM Service Manual Online
For 1990-2009 cars only

Important Preliminary Checks

Before Starting

Before using this section, perform the Diagnostic System Check - Vehicle in Vehicle DTC Information and verify all of the following conditions:

    • The powertrain control module (PCM), malfunction indicator lamp (MIL), and check engine are operating correctly.
    • There are no diagnostic trouble codes (DTCs) stored.
    • Scan tool data is within normal operating range. Refer to Scan Tool Data List .

Verify the customer complaint, and locate the correct symptom in the table of contents. Check the items indicated under that symptom.

Visual/Physical Check

Several of the symptom procedures call for a careful visual/physical check. The importance of this step cannot be stressed strongly enough. This step can lead to correcting a problem without further checks and can save valuable time. This check should include:

    • PCM grounds for the following conditions:
       - Clean connection
       - Tight connection
       - Proper location
       - Refer to Power and Grounding Component Views in Wiring Systems.
    • Vacuum hoses for the following conditions:
       - Splits
       - Kinks
       - Proper connections as shown on the Vehicle Emission Control Information label--Refer to Emission Hose Routing Diagram .
       - Leaks
       - Restrictions
    • Air leaks at the following components:
       - Throttle body mounting
       - Intake manifold sealing surfaces
    • Wiring for the following conditions:
       - Proper locations
       - Pinches
       - Cuts
    • Use the following tables when diagnosing a symptom complaint:
       -  Hard Start
       -  Surges/Chuggles
       -  Lack of Power, Sluggishness, or Sponginess
       -  Detonation/Spark Knock
       -  Hesitation, Sag, Stumble
       -  Cuts Out, Misses
       -  Poor Fuel Economy
       -  Poor Fuel Fill Quality
       -  Rough, Unstable, or Incorrect Idle and Stalling
       -  Dieseling, Run-On
       -  Backfire
       -  Malfunction Indicator Lamp (MIL) Inoperative
       -  Malfunction Indicator Lamp (MIL) Always On