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 true:

• | The PCM is OK

• | The malfunction indicator lamp (MIL) is OK

• | No DTCs are stored

• | The scan tool data is within a normal operating range. Refer to Scan Tool Data List .

Verify the customer complaint and locate the correct symptom in the table of contents. Inspect 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 too strongly. The visual/physical check can lead to correcting a problem without further diagnostics and save valuable time. This inspection should include the following concerns:

• | The PCM grounds are clean and tight and in the correct locations.

• | The vacuum hoses are OK and connected correctly as shown on Vehicle Emission Control Information label.

• | There are no vacuum leaks at the throttle body mounting and the intake manifold sealing surfaces.

• | The wiring is OK and correctly positioned.

### Intermittents

Important: A problem may or may not turn on the MIL or store a DTC. DO NOT use the DTC tables for intermittent problems. The fault must be present in order to locate the problem.

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

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

• | An incorrectly formed terminal or a damaged terminal.

• | All of the connector terminals in the faulty circuit should be carefully tested for the correct contact tension.

• | A faulty terminal to wire connection. This may require removing the terminal from the connector body in order to inspect the connection.

The vehicle may need to be driven with a DMM connected to the 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 tool's 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 test for loss of DTC memory, disconnect the throttle position (TP) sensor and idle the engine until the MIL illuminates. DTC P0122 should be stored and kept in memory when the ignition is turned off. If the DTC is not stored, the PCM is faulty. When this test is complete, make sure that you clear the DTC P0122 from memory.

An intermittent MIL with no stored DTC may be caused by the following concerns:

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

• | An MIL wire to the PCM shorted to ground.

• | Any faulty PCM grounds

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

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

• | A malfunctioning relay

• | A PCM driven solenoid

• | A switch

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

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

All of the ignition control module (ICM) wiring should be routed away from the generator. Inspect all of the wires from the PCM to the ICM for faulty connections.

Test for an open diode across the A/C compressor clutch, or other open diodes.