Symptoms - Engine Controls

Symptoms - Engine Controls

Before Using This Section
Before using this section, you should have performed the Diagnostic System Check Engine Controls and determined that the following criteria:
1. The control module and the malfunction indicator lamp (MIL) are operating correctly.
2. There are no diagnostic trouble codes (DTCs) stored, or a DTC exists but without the MIL.

Several of the following symptom procedures call for a careful visual and physical check. The visual and physical checks are very important. The checks can lead to correcting a problem without further checks which may save valuable time.

Visual and Physical Checks

Check the following items:
- The control module grounds for being clean, tight, and in their proper location.
- The wiring for the following items:
- Proper connections
- Pinches
- Cuts

- The following symptom tables contain groups of possible causes for each symptom. The order of these procedures is not important. If the scan tool readings do not indicate the problems, then proceed in a logical order, easiest to check or most likely to cause first. In order to determine if a specific vehicle is using a particular system or component, refer to Engine Controls Schematics for an application.

Verify Customer's Concern
Locate the correct symptom table. Check the items indicated under that symptom from the following symptom tables:
- Intermittent Conditions
- Hard Start
- Surges/Chuggles
- Lack of Power, Sluggishness, or Sponginess
- Fuel Knock/Combustion Noise
- Hesitation, Sag, Stumble
- Cuts Out, Misses
- Poor Fuel Economy
- Rough, Unstable, or Incorrect Idle and Stalling
- Engine Starts and Stalls
- Idle Control Error
- Excessive Smoke (Black Smoke) or Excessive Smoke (Blue or Gray Smoke)or Excessive Smoke (White Smoke)

Intermittent Conditions
An intermittent condition may or may not turn on the malfunction indicator lamp (MIL) or store a diagnostic trouble code (DTC).

Preliminary Checks
Perform a visual check to locate the cause of the problem.
- Refer to Symptoms - Engine Controls.
- The fault must be present to locate the problem. If a fault is intermittent, the use of DTC tables may result in the replacement of good parts.
- Check for loss of DTC memory by disconnecting the engine coolant temperature (ECT) sensor and idling the engine until the MIL turns ON. An ECT DTC should store and remain in memory when turning OFF the ignition for at least 30 seconds. If not, the ECM is malfunctioning.

Electrical Connections or Wiring
Poor electrical connections or wiring can cause most intermittent problems. Perform a careful check of the suspected circuit for the following:
- Check for poor mating of the connector halves, or terminals not fully seated in the connector body, backed-out.
- Check for improperly formed or damaged terminals. Carefully reform or replace all the connector terminals in the problem circuit to ensure the proper contact tension.
- Check for poor terminal to wire connections. This requires removing the terminal from the connector body to check.

Road Test
If a visual/physical check does not locate the cause of the problem, drive the vehicle with a DMM connected to a suspected circuit or use a scan tool. An abnormal voltage or scan reading, when the problem occurs, indicates the problem may be in that circuit.

Intermittent Malfunction Indicator Lamp (MIL)
The following can cause an intermittent MIL and no DTCs:
- Electrical system interference caused by a malfunctioning relay, engine control module (ECM) driven solenoid, or switch. The electrical component can cause a sharp electrical surge. Normally, the problem will occur when the malfunctioning component is operating.
- The improper installation of electrical devices; such as lights, 2-way audios, electric motors, etc.
- The MIL circuit intermittently shorted to ground.
- Poor ECM grounds