GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Oldsmobile 🢒 1999 🢒 Alero 🢒 Engine 🢒 Engine Controls - 3.4L 🢒 Intermittent Conditions

Checks

Action

Definition: The problem is not currently present but is indicated in DTC History.

OR

There is a customer complaint, but the symptom can not currently be duplicated (if the problem is not DTC related).

Preliminary Checks

The fault must be present to locate a problem using the DTC table. If a fault is intermittent, the use of DTC Tables may result in the replacement of good parts.

Harness/Connector Check

Many intermittent open or shorted circuits come and go with harness/connector movement caused by vibration, engine torque, bumps/rough pavement, etc.. Check for this type of condition by performing the applicable procedure from the following list:

    • Move related connectors and wiring while monitoring the appropriate scan tool data.
    • Move related connectors and wiring with the component commanded on (and off) with the scan tool. Observe the component's operation.
    • With the engine running, move related connectors and wiring while monitoring engine operation.

If harness or connector movement affects the data displayed, component/system operation, or engine operation inspect and repair the harness/connections as necessary. Refer to Electrical Connections or Wiring below.

Duplicating Failure Conditions

Freeze Frame/Failure Records data (where applicable) can be used to duplicate the conditions under which a DTC sets.

  1. Review and record Freeze Frame/Failure Records data
  2. Clear DTCs using the scan tool.
  3. Turn the key to Off and wait 15 seconds.
  4. Operate the vehicle under the same conditions that were noted in Freeze Frame/Failure Records data (as closely as possible). The vehicle must also be operating within the conditions for running the DTC. Refer to Conditions for Running the DTC.
  5. Monitor DTC Status for the DTC being tested. The scan tool will indicate Ran, when the enabling conditions have been satisfied long enough for the DTC to run. The scan tool will also indicate whether the DTC passed or failed.

An alternate method is to drive the vehicle with DMM J 39200 connected to a suspected circuit. An abnormal reading on the DMM when the problem occurs, may help you locate the problem.

Scan Tool Snapshot

The scan tool can be set up to take a 'snapshot' of the parameters available via serial data. The Snapshot function records live data over a period of time. The recorded data can be played back and analyzed. The scan tool can also graph parameters singly or in combinations of parameters for comparison. The snapshot can be triggered manually at the time the symptom is noticed, or set up in advance to trigger when a DTC sets.

An abnormal value captured in the recorded data may point to a system or component that needs to be investigated further.

Refer to the scan tool user instructions for more information on the Snapshot function.

Electrical Connections or Wiring

Poor electrical connections/terminal tension or wiring problems 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. Check for poor terminal tension.
    • Check for poor terminal to wire connections including terminals crimped over insulation. This requires removing the terminal from the connector body to check.
    • Check for corrosion/water intrusion.

Refer to Wiring Repairs .

Check for harness problems which include the following:

    • Pinched, cut or rubbed through wiring.
    • A misrouted harness that is too close to high voltage/high current devices such as secondary ignition components, motors, generator etc. These components may induce electrical noise on a circuit that could interfere with normal circuit operation.
    • Improper installation of non-factory (aftermarket) add on accessories.

Intermittent Malfunction Indicator Lamp (MIL) with NO DTCs

The following conditions may cause an intermittent MIL and no DTCs:

    • Electrical system interference caused by a malfunctioning relay, PCM driven solenoid or switch. They can cause a sharp electrical surge. Normally, the problem will occur when the malfunctioning component is operating.
    • Improper installation of non-factory (aftermarket) add on accessories such as lights, 2-way radios, electric motors, etc.
    • The Malfunction Indicator Lamp (MIL) circuit intermittently shorted to ground.
    • Poor PCM grounds.

If the MIL can be commanded on and off with the scan tool, none of the above conditions are present, and no DTCs are set, re-program the PCM with the most current calibration software and recheck MIL operation. Refer to Powertrain Control Module Replacement/Programming .

Loss of DTC Memory

In order to check for loss of DTC memory, perform the following test:

  1. Disconnect the Engine Coolant Temperature (ECT) sensor.
  2. Start the engine.
  3. Monitor DTC Status for DTC P0118 using a scan tool.
  4. Allow the engine to idle until the DTC P0118 diagnostic runs and fails.
  5. Turn the key to Off and wait at least 30 seconds.
  6. Turn the key to Run.
  7. Check for DTCs using the scan tool.

The scan tool should indicate DTC P0118 Failed Since Code Clear. The PCM should store and retain this information in memory even after turning off the ignition for at least 30 seconds (the information should be stored for 40 ignition key cycles as long as the PCM battery feed and ground circuits are uninterrupted). If the DTC info is not retained, and the PCM power and grounds check out OK, the PCM is malfunctioning.

Additional Checks

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

Check for improper installation of non-factory (aftermarket) add on accessories such as lights, 2-way radios, electric motors, etc.

Check the generator for a bad rectifier bridge that may be allowing AC noise into the electrical system.