GM Service Manual Online
For 1990-2009 cars only

Important Preliminary Checks

Checks

Action

Before Using This Section

Before using this section, you should have performed the Powertrain On-Board Diagnostic System Check . Refer to Powertrain On Board Diagnostic (OBD) System Check . Several of the following symptom procedures call for a careful visual and physical check. The visual and physical checks are very important. These checks can lead to correcting a problem which may save valuable time.

Visual and Physical Checks

    • Check the VCM grounds for being clean, tight and in their proper location. Refer to Vehicle Control Module Description .
    • Check the vacuum hoses for splits, kinks and proper connections, as shown on the Vehicle Emission Control Information label.
    • Check thoroughly for any type of leak or restriction.
    • Check for air leaks at all the mounting areas of the intake manifold sealing surfaces.
    • Check the ignition wires for the following conditions:
       - Cracking
       - Hardness
       - Proper routing
       - Carbon tracking
    • Check the wiring for the following items:
       - Proper connections
       - Pinches
       - Cuts
    • The following symptom tables contain groups of possible causes for each symptom and cover several engines. The following symptom tables cover several engines. The order of these procedures is not important. If the scan tool readings do not indicate the problems, then proceed in a logical order, easiest to check or most likely to cause first. In order to determine if a specific vehicle is using a particular system or component, refer to the Control Module Wiring Diagrams for an application.

Symptom

  1. Verify the customer complaint.
  2. Locate the correct symptom table.
  3. Check the items indicated under that symptom.

Use the following tables when diagnosing a symptom complaint.

    •  Hard Start
    •  Surges/Chuggles
    •  Detonation/Spark Knock
    •  Cuts Out, Misses
    •  Poor Fuel Economy
    •  Dieseling, Run-On
    •  Backfire