For 1990-2009 cars

### Important Preliminary Checks

#### Before Starting

Before using this section you should have performed the Powertrain On-Board Diagnostic (OBD) System Check and determined that the following items are OK:

• | The PCM and MIL, check engine, are operating correctly.

• | There are no DTCs stored.

• | Scan tool 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.

### 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

• | Vacuum hoses for the following conditions:

- | Splits

- | Kinks

- | Proper connections as shown on Vehicle Emission Control Information label

- | Leaks

- | Restrictions

• | Air leaks at the following components:

- | Throttle body mounting

- | Intake manifold sealing surfaces

• | Wiring for the following conditions:

- | Proper locations

- | Pinches

- | Cuts

### Intermittents

Important: Problem may or may not turn ON the malfunction indicator lamp (MIL) 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 careful visual and physical check. Check for the following conditions:

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

• | Improperly formed or damaged terminal.

• | All electrical connector terminals in the problem circuit should be carefully checked for proper contact tension.

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

The vehicle may be driven with a DMM connected to a suspected circuit. An abnormal voltage is a good indication that there is a malfunction in the circuit being monitored.

A scan tool can be used to help detect intermittent conditions. The scan tool has several features that can be used to locate an intermittent condition.

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 can also aid in locating an intermittent condition. Review and record the information in the Freeze Frame associated with the intermittent DTC being diagnosed. The vehicle can be driven within the conditions that were present when the DTC originally set.

To check loss of DTC memory, disconnect TP sensor and idle engine until the MIL, check engine, comes ON. DTC P0122 should be stored and kept in memory when ignition is turned OFF. If not the PCM is faulty. When this test is completed, make sure that you clear the DTC P0122 from memory.

An intermittent MIL, check engine, with no stored DTC may be caused by the following:

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

• | MIL, check engine, wire to PCM shorted to ground.

• | Poor PCM grounds

If the intermittent condition exists as a start and then stall, check for DTCs relating to the vehicle theft deterrent system.

Check for an electrical system interference caused by the following components:

• | Malfunctioning relay

• | PCM driven solenoid

• | Switch

They can cause a sharp electrical surge. Normally, the problem will occur when the malfunctioning component is operated.

Check for improper installation of electrical options such as lights, cellular phones, etc.

All ignition control module (ICM) wiring should kept away from the generator. Check all wires from the PCM to the ignition control module for poor electrical connections.

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