BCM TROUBLE CODE DIAGNOSIS ADD CODE 124-VSS CIRCUIT

VEHICLES AFFECTED: 1989 3800 (VIN C) BUICK "E"

This diagnostic procedure for Code B124 (Vehicle Speed Sensor Circuit) is to supplement the 1989 New Product Service Information Manual. The attached facing page and chart should be added as a NEW Section "8D2 - BCM Trouble Code Diagnosis". The mechanization and procedure changed from 1988 to 1989. Use this diagnostic procedure for all 1989 Riviera's and Reatta's.

CODE B124

VEHICLE SPEED SENSOR CIRCUIT

Circuit Description:

The vehicle speed sensor uses a permanent magnet (P.M.) generator to produce an oscillating electrical signal representative of vehicle speed. This signal is sent to the ECM by CKTS 400 (VSS HI) & 401 (VSS LO) where the ECM buffers and amplifies the signal. Output voltage of the generator can be read by using a digital voltmeter on the 2V AC scale while rotating the generator drive (rotate front wheels).

Code B124 will set if the following conditions are present for 30 seconds:

Ignition "ON" No Code B334 Transaxle in 4th gear Vehicle speed is zero Engine RPM greater than 1300 Condition occurs for at least 10 seconds OR Ignition "ON" No Code B334 Vehicle speed is zero

Code BI24 currently set

During the time the failure is present the cruise control and continuous compressor at idle will be disabled. Vehicle speed reading BD60 will display actual sensor reading.

Test Description:

Numbers below refer to circled numbers on the diagnostic chart.

1. Since the ECM amplifies and buffers the speed signal before it is sent to the BCM, Code E024 in the ECM may set along with Code B124 in the BCM. If Code B124 sets with Code E024, refer to diagnosis for Code E024.

Note on Intermittents

If an intermittent Code B124 has been set, manipulate the related wiring, while observing BCM data parameter BD60. If a failure is induced, the reading will jump from a normal value to zero.

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.