GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2002 🢒 Express 🢒 Transmission/Transaxle 🢒 Automatic Transmission - 4L80-E 🢒 Intermittent Conditions

Checks

Action

DEFINITION: The problem may or may not turn ON the malfunction indicator lamp (MIL) or store a diagnostic trouble code (DTC).

Preliminary Checks
    • 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.

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 conditions:

    • Poor mating of the connector halves
    • Backed out terminals--Terminals not fully seated in the connector body
    • Improperly formed or damaged terminals--Carefully reform or replace all the connector terminals in the problem circuit to ensure the proper contact tension.
    • Poor terminal to wire contact--Check for poor terminal to wire connections by removing the terminal from the connector body and inspecting the terminal.

Road Test

If a visual and physical check does not locate the cause of the problem, drive the vehicle with a DMM connected to the 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, powertrain control module (PCM) driven solenoid, or switch--All of these 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 radios, electric motors, etc.
    • The malfunction indicator lamp (MIL) circuit intermittently shorted to ground
    • Poor PCM grounds

Loss of DTC Memory

Check for loss of DTC memory by disconnecting the engine coolant temperature (ECT) sensor and idling the engine until the MIL turns ON. An engine coolant temperature (ECT) DTC should store and remain in memory when turning OFF the ignition for at least 10 seconds. If not, the PCM is malfunctioning.

Additional Checks

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