PCM/BCM - Lack of Communication Between Units

91buick06

Bulletin: 91-6E-19

Date: June '91

Ref. No.: 91-195-6E

Corp. Ref. No.: 106502


SUBJECT: INTERRUPTION OF PCM - BCM COMMUNICATION WHEN A DIAGNOSTIC
TOOL IS CONNECTED TO THE SERIAL DATA (ALDL) CONNECTOR (NEW
REVISED MEM-CAL)

MODELS AFFECTED: 1991 RIVIERA AND REATTA MODELS WITH 3800 T.P.I. (VIN L)


Breakpoints are as follows:
Riviera Federal Calib. MU409849 Calif. Calib. MU409802
Reatta Federal Calib. MB900565 Calif. Calib. MB900548

Some 1991 Riviera and Reatta vehicles equipped with 3800 T.P.I. (VIN L) engine, built prior to the VINS listed, may have a condition that prevents the PCM from communicating with the BCM when a diagnostic tool is connected to the vehicles serial data (ALDL) connector. This condition only occurs when a diagnostic tool is connected to the vehicles ALDL connector.

Should this condition exist on a vehicle, technicians may observe specific functions that are affected.

^ A/C clutch remains on or off
^ BCM Code 334 (BCM-PCM communication error) is stored
^ Coolant temperature gauge and tachometer are not displayed

This condition may lead to improper diagnosis and unnecessary repairs. It is recommended that a new revised calibration mem-cal be installed.

The mem-cals are currently available through GMSPO under the following part numbers.

Model Axle Scanner I.D. Broadcast Service
Year Application Ratio With This Code Part #
Mem-cal Installed

1991 Riviera 3.06 Fed. 1464 AXMU 16162582
1991 Riviera 3.06 Calif. 1474 AXMW 16162586
1991 Reatta 3.33 Fed. 1484 AXMX 16162590
1991 Reatta 3.33 Calif. 1494 AXMY 16162594

WARRANTY INFORMATION:

Use applicable labor operation and time for mem-cal replacement.