GM: Electra/Park Avenue/Ninety-Eight 1990-1993

Intermittent Faults


Faults which occur intermittently are difficult to diagnose. When diagnosing such problems, keep an overall view of system function in mind. Faults may result from low system voltage, low brake fluid in the pmv reservoir or any interruption of the signal(s) from the wheel speed sensor(s). Any condition interrupting the power supply to the ebcm or hydraulic unit will also cause the dash warning lamp to illuminate. Most intermittent or random faults relate to loose connectors or faulty terminals. Again, the visual inspection is of prime importance.

The diagnostic codes can be helpful in tracking intermittent faults. While not designated History or Current, certain combinations can point to fault status. Stored codes which do not light the antilock warning lamp are intermittent or history codes. If the antilock lamp is lit and one or more codes are stored, at least 1 (or more) of the codes is current.

Additionally, when diagnosing intermittent faults, keep the following lowing system basics in mind:

It is possible to feel the system self-test at very low speed if the brake pedal is barely applied. Both the sound (fluid returning to the master cylinder) and the slight vibration (valves cycling through test mode) are normal conditions.
Any fault in the anti-lock system will light the traction light. When both lamps are lit, diagnose the abs system.
The systems will disable if either the ebcm senses overheating in the brakes or transaxle. Once cooled, the abs/tcs becomes available and the dash lamp(s) extinguish. This self-protective operation is completely normal but may become a source of operator concern.
When diagnosing an apparent tcs fault, make certain the tcs off switch is not engaged.
If a faulty wheel speed signal is suspected, check tires and wheels for matching sizes and tire pressures.

If necessary, the vehicle must be test driven to recreate circumstances causing the fault.

The operator of the vehicle is the best source of information about fault occurrences. An accurate description of driving conditions will allow the fault to be duplicated during the test drive.

  1. Display, record and clear all fault codes in the ebcm.
  3. Test drive the vehicle, attempting to recreate the failure conditions.
  5. Safely stop the vehicle. Display and record the stored codes, if any.

Clearing Fault Codes

Stored fault codes must be cleared using the bi-directional hand scanner. After repairs are completed, clear all stored codes and test drive the vehicle. Recheck for any newly-stored codes after the test drive.