For 1990-2009 cars

Important Preliminary Checks Before Starting

Before using the Symptom Tables, you should have performed the Powertrain On Board Diagnostic (OBD) System Check and verify all of the following are true:

• | The PCM and MIL (Service Engine Soon) are operating correctly.

• | There are no DTC(s) stored.

• | Scan data is within normal operating range, refer to Engine 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.

Several of the symptom procedures call for a Careful Visual/Physical Check. The importance of this step cannot be stressed too strongly - it can lead to correcting a problem without further checks and can save valuable time. This check should include:

• | PCM grounds for being clean, tight, and in their proper location.

• | 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.

• | Mass Air Flow (MAF) sensor installation. The arrows on the plastic portion of the sensor must point toward the engine.

• | Air intake ducts for collapsed or damaged areas.

• | Air leaks at throttle body mounting area, Mass Air Flow (MAF) sensor and intake manifold sealing surfaces.

• | Ignition wires for cracking, hardness, proper routing and carbon tracking.

• | Wiring for proper connections, pinches and cuts.

Intermittents

Important: Problem may or may not turn ON the MIL (Malfunction Indicator Lamp) or store a DTC. DO NOT use the Diagnostic Trouble Code (DTC) tables for intermittent problems. The fault must be present to locate the problem.

Most intermittent problems are caused by faulty electrical connections or wiring. Perform a careful visual/physical check for the following conditions:

• | Poor mating of the connector halves or a terminal not fully seated in the connector body (backed out).

• | Improperly formed or damaged terminal.

• | All connector terminals in the problem circuit should be carefully reformed or replaced to insure proper contact tension.

• | Poor terminal to wire connection. This requires removing the terminal from the connector body to check.

Road test the vehicle with a J 39200 Digital Multimeter connected to a suspected circuit. An abnormal voltage when the malfunction occurs, is a good indication that there is a malfunction in the circuit being monitored.

Use a Scan Tool to help detect intermittent conditions. The GM Techline equipment (Scan Tool) have several features that can be used to locate an intermittent condition. Use the following features to find intermittent faults:

• | The Snapshot feature can be triggered to capture and store engine parameters within the scan tool when the malfunction occurs. This stored information then can be reviewed by the service technician to see what caused the malfunction.

• | Using a Scan Tools Freeze Frame buffer or Failure Records buffer can also aid in locating an intermittent condition. Review and capture the information in the freeze frame or failure record associated with the intermittent DTC being diagnosed. The vehicle can be driven in the conditions that were present when the DTC originally set.

Loss of diagnostic code memory. To check, disconnect MAP sensor and idle engine until the MIL (Malfunction Indicator Lamp) comes ON (The engine speed may require to be increased to 2000 RPM). DTC P0107 should be stored and kept in memory when ignition is turned OFF. If not the PCM is faulty. When this test is completed, DTC P0107 should be cleared from memory.

An intermittent MIL (Malfunction Indicator Lamp) with no stored DTC may be caused by the following:

• | Ignition coil shorted to ground and arcing at ignition wires or spark plugs.

• | PCM grounds, refer to PCM wiring diagrams.

If the intermittent condition exists as a start and then stall, check for DTC(s) relating to the theft deterrent system. Check for improper installation of electrical options such as lights, cellular phones etc.

All Ignition Control (IC) wires should be routed away from secondary ignition wires, distributor, coil, and generator. All wires from the PCM to distributor should have a good connection.

Check for open diode across A/C compressor clutch and for other open diodes.