A Symptoms

SYMPTOMS - ENGINE CONTROLS

IMPORTANT PRELIMINARY CHECKS

BEFORE STARTING
Before using this section, you should have performed the Diagnostic System Check-Computers and Control Systems and determined that the following items are OK:
- The powertrain control module (PCM), malfunction indicator lamp (MIL), and check engine are operating correctly.
- There are no diagnostic trouble codes (DTCs) stored.
- Scan tool data is within normal operating range. Refer to Scan Tool Data List. Scan Tool Data, Normal Values and Definitions

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
Refer to Power and Grounding Component Views in Diagnostic Aids.

- Vacuum hoses for the following conditions:
- Splits
- kinks
- Proper connections as shown on the Vehicle Emission Control Information label-Refer to Emission Hose Routing Diagram.
- Leaks
- Restrictions

- Air leaks at the following components:
- Throttle body mounting
- Intake manifold sealing surfaces

- Wiring for the following conditions:
- Proper locations
- Pinches
- Cuts

- Use the following tables when diagnosing a symptom complaint:
- Hard Stan
- 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
- Malfunction Indicator Lamp (MIL) Inoperative
- Malfunction Indicator Lamp (MIL) Always On

Intermittent Conditions

IMPORTANT: The condition may or may not illuminate the malfunction indicator lamp (MIL) or store a diagnostic trouble code (DTC). The fault must be present to be diagnosed.

Most intermittent conditions are caused by faulty electrical connections or wiring. Perform a careful visual/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

Refer to Connector Repairs in Diagnostic Aids.

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 the throttle position (TP) sensor and idle the engine until the MIL, check engine, comes ON. DTC P0122 should be stored and kept in memory when the ignition is turned OFF. If not the powertrain control module (PCM) is faulty. When this test is completed, make sure that you clear the DTC P0122 from memory.

An intermittent malfunction indicator lamp (MIL), check engine, with no stored DTC may be caused by the following:
- The ignition coil shorted to ground and arcing at ignition wires or plugs
- The MIL, check engine, wire to PCM shorted to ground
- A 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:
- A malfunctioning relay
- The PCM driven solenoid
- A 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.