VEHICLE SPEED READING INCORRECT IN GEAR AT IDLE. Cadillac Allante 1987

For 1990-2009 cars

# VEHICLE SPEED READING INCORRECT IN GEAR AT IDLE

#### VEHICLES AFFECTED: 1987 ALLANTE (V)

Some 1987 Allantes may experience an incorrect vehicle speed display on the digital speedometer while at a stop, with the transaxle in gear and engine idling (correct vehicle speed display is zero). The incorrect vehicle speed may be caused by an open or shorted diode in the rectifier bridge of the generator. This condition may not set charging system related BCM Codes B409, B410 or B411 or ECM Code E016. One or all of the following symptoms may also occur when an incorrect vehicle speed is displayed:

- Idle - 1200 RPM in Park 900 RPM in gear

- Poor performance and/or erratic shifts (on deceleration to a stop, on acceleration from idle, and at actual vehicle speed of less than 3 mph).

Diagnosis

1. Start engine, place foot firmly on brake pedal and place transmission in drive. Note veHicle digital speedometer reading.

2. If the digital speedometer reading is other than 0 mph, enter diagnostics and select BCM override BS06 "Generator Disable." Refer to Section 8D in the 1987 Allante Service Information Manual for the procedure to enter diagnostics and BCM override selection. Depressing and holding the warmer button while in BCM override BS06 will disable the generator. Nbte digital speedometer reading with the generator disabled and proceed as follows:

- 0 mph Digital Speedometer Speed Reading - Check for a shorted or open diode in the rectifier bridge. See figure 1 for diode checking procedure.

- Other than 0 mph Digital Speedometer Speed Reading - Refer to Page 8A-33 of the 1987 Allante Service Information Manual, Vehicle Speed Sensor Diagnosis.

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.