GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Oldsmobile 🢒 2001 🢒 Aurora 🢒 Engine 🢒 Engine Electrical 🢒 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 Inspection

Refer to Symptoms - Engine Controls , Important Preliminary Checks Before Starting.

Harness and Connector

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

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

If a harness or connector movement affects the data displayed, the component or system operation, or the engine operation, inspect and repair the harness and connections as necessary.

Refer to Electrical Connections or Wiring in this table.

Electrical Connections and Wiring

Poor electrical connections and terminal tension, or wiring problems cause most intermittents. Perform a careful inspection of the suspected circuit for the following connections:

    • Inspect for poor mating of the connector halves, or terminals not fully seated in the connector body.
    • Inspect for improperly formed or damaged terminals. Test for poor terminal tension.
    • Inspect for poor terminal to wire connections including terminals crimped over the insulation. This requires removing the terminal from the connector body.
    • Inspect for corrosion and water intrusion. Pierced or damaged insulation can allow moisture to enter the wiring. The conductor can corrode inside the insulation with little visible evidence. Look for swollen and stiff sections of wire in the suspect circuits.
    • Inspect for wires that are broken inside the insulation.
    • Inspect the harness for pinched, cut, or rubbed through wiring.
    • Make sure the wiring does not come in contact with hot exhaust components.

Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Control Module Power and Grounds

Component Power and Grounds

Poor power or ground connections can cause widely varying symptoms.

    • Test all of the control module power circuits. Many vehicles have multiple circuits supplying power to the control module. Other components in the system may have separate power circuits that may also need to be tested. Inspect the connections at the module or component connectors, the fuses, and any intermediate connections between the power source and the module or component. A test lamp or a DMM may indicate that voltage is present, but neither tests a circuit's ability to carry sufficient current. Ensure that the circuit can carry the current necessary to operate the component. Refer to Power Distribution Schematics in Wiring Systems.
    • Test all control module ground and system ground circuits. The control module may have multiple ground circuits. Other components in the system may have separate grounds that may also need to be tested. Inspect the grounds for clean and tight connections at the grounding point. Inspect the connections at the component and in splice packs, where applicable. Ensure that the circuit can carry the current necessary to operate the component. Refer to Ground Distribution Schematics in Wiring Systems.

Temperature Sensitivity

An intermittent condition may occur when a component or connection reaches a normal operating temperature. The condition may occur only when the component or connection is cold, or only when the component or connection is hot.

The Freeze Frame, the Failure Records, the Snapshot, and the Vehicle Data Recorder data may help with this type of intermittent condition, where applicable.

If the intermittent is related to heat, review the data for a relationship with the following conditions:

    • Any high ambient temperatures
    • Any underhood, engine generated heat
    • Any circuit generated heat due to a poor connection or a high electrical load
    • Any igher than normal load conditions such as towing, etc.

If the intermittent is related to cold, review the data for the following conditions:

    • Any low ambient temperatures--In extremely low temperatures, ice may form in a connection or component. Check for water intrusion.
    • The condition only occurs on a cold start.
    • The condition goes away when the vehicle warms up.

Information from the customer may help to determine if the trouble follows a pattern that is temperature related.

Electromagnetic Interference (EMI) and Electrical Noise

Some electrical components and/or circuits are sensitive to EMI or other types of electrical noise. Inspect for the following conditions:

    • A misrouted harness that is too close to high voltage or high current devices such as the secondary ignition components, the motors, the generator, etc. These components may induce electrical noise on a circuit that could interfere with normal circuit operation.
    • Any electrical system interference caused by a malfunctioning relay, a PCM driven solenoid, or a switch--This can cause a sharp electrical surge. Normally, the problem will occur when the malfunctioning component is operating.
    • The improper installation of aftermarket add on accessories such as lights, 2-way radios, amplifiers, electric motors, remote starters, alarm systems, cell phones, etc.
    • Test for an open diode across the A/C compressor clutch and for other open diodes. Some relays may contain a clamping diode.
    • Test the generator for a bad rectifier bridge that may be allowing AC noise into the electrical system. Refer to Diagnostic Starting Point - Engine Electrical in Engine Electrical.

Incorrect PCM Programming

There are only a few situations where reprogramming a PCM is appropriate:

    • When a new service PCM is installed
    • When a PCM from another vehicle is installed
    • When revised software or calibration files have been released for this vehicle

Important::  DO NOT re-program the PCM with the same software and calibration files that are already present in the PCM. This is not an effective repair for any type of driveability problem.

Verify that the PCM contains the correct software and calibration. If incorrect programming is found, re-program the PCM with the most current software or calibration. Refer to Powertrain Control Module Replacement .

Duplicating Failure Conditions

If none of the previous checks are successful, attempt to duplicate and/or capture the Failure Conditions.

The Freeze Frame and Failure Records data contains the conditions that were present when the DTC set.

  1. Review and record the Freeze Frame and Failure Records data.
  2. Clear any 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 the Freeze Frame and Failure Records data as closely as possible. The vehicle must also be operating within the Conditions for Running the DTC. Refer to the Conditions for Running the DTC in the supporting text of the DTC being diagnosed.
  5. Monitor the 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 a DMM 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 a component that needs to be investigated further.

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

Vehicle Data Recorder

The vehicle data recorder is connected to the data link connector (DLC) and sent with the customer. The J 42598 captures data for later retreival and analysis by the technician. Refer to the J 42598 user instructions for more information.