INTERRUPT. OF PCM/BCM WHEN DIAG. TOOL IS CONNECTED

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.

o A/C clutch remains on or off o BCM Code 334 (BCM-PCM communication error) is stored o 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.

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.