SERVICE MANUAL UPDATE-SEC. 5E1 ABS VI DIAG. TROUBLE CODE A031

Subject: ANTILOCK BRAKE SYSTEM ABS Vi DIAGNOSTIC TROUBLE CODE A031 ADDED

Model and Year: 1993 CORSICA AND BERETTA

This bulletin updates the 1993 Corsica/Beretta Service Manual by adding diagnostic trouble code A031 diagnostics. Please add the attached diagnostic chart and facing page to Section 5El, "Antilock Brake System."

Circuit Description:

As the toothed ring passes by the wheel speed sensor, changes in the electromagnetic field causes the wheel speed sensor to produce a sinusoidal (AC) voltage signal with magnitude and frequency proportional to wheel speed

Failure Condition:

Diagnostic trouble code A031 can be set when the vehicle is not in an ABS stop and the parking brake is "OFF." If for 20 seconds two wheel speeds = 0 and the vehicle speed is greater than 16 km/h (10 mph), a malfunction exists.

Action Taken:

A malfunction diagnostic trouble code is stored, ABS is disabled and the ABS indicator lamp is turned "ON".

Test Description: Number(s) below refer to circled number(s) on the diagnostic chart.

1. This step verifies whether the malfunction is currently present.

2. This step determines if diagnostic trouble codes other than A031 are set.

3. This step identifies if the malfunction is common to both rear wheel speed sensor circuits.

4. Since both rear sensors are common to the rear ABS harness, the rear ABS harness/body to ABS and fuel sender connection should be inspected.

Diagnostic Aids:

A false diagnostic trouble code A031 may be set as a result of vehicle operation while on a hoist or while stuck in mud or snow. An "Intermittent" malfunction may be caused by a poor connection, rubbed through wire insulation or a wire that is broken inside the insulation. The frequency of the malfunction can be checked by using the enhanced diagnostic function of the Tech 1, as described in "Enhanced Diagnostics," found in the service manual (Section 5EI).

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.