GM Service Manual Online
For 1990-2009 cars only

Preliminary Checks Before Starting

Important:  Before using the Symptom tables use the following:

   •  Perform Diagnostic System Check - Engine Controls and verify all of the following items:
      -  Ensure there are no DTCs stored.
      - The Scan tool data is within normal operating range. Refer to Scan Tool Data List .
   •  Verify the customer complaint.
   •  Perform the Visual/Physical Check in this section.

Locate the correct symptom in the list at the end of this section. Follow the procedures in the appropriate diagnostic table. If the condition can not be duplicated, or is determined to be intermittent, refer to Intermittent Conditions .

Visual/Physical Check

Notice: Use the connector test adapter kit J 35616-A for any test that requires probing the following items:

   • The PCM harness connectors
   • The electrical center fuse/relay cavities
   • The component terminals
   • The component harness connector
Using this kit will prevent damage caused by the improper probing of connector terminals.

Several of the symptom procedures call for a careful visual and physical inspection. This can lead to correcting a condition without further tests and can save valuable time. This inspection should include the following areas:

    •  Inspect the PCM grounds for being clean, tight, and in their proper location. Refer to Master Electrical Component List and Power and Grounding Connector End Views in Wiring Systems.
    •  Inspect vacuum hoses for splits, kinks, and proper connections, as shown on Vehicle Emission Control Information label. Inspect thoroughly for any type of leak or restriction. Refer to Emission Hose Routing Diagram .
    •  Inspect the air intake ducts for being collapsed, damaged areas, looseness, improper installation, or leaking, especially between the MAF sensor and the throttle body.
    • Inspect for air leaks at throttle body mounting area, mass airflow (MAF) sensor and intake manifold sealing surfaces.
    •  Inspect the wiring harness for poor connections, pinches, cuts, or other damage.
    •  Inspect for loose, damaged, or missing sensors/components.

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
    •  Engine Cranks but Does Not Run
    •  Malfunction Indicator Lamp (MIL) Inoperative
    •  Malfunction Indicator Lamp (MIL) Always On