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

SUBJECT: INTERRUPTION OF PCM-BCM COMMUNICATION WHEN A DIAGNOSTIC TOOL IS CONNECTED TO THE ALDL - INSTALL A REVISED MEMCAL

MODELS/YEARS: 1991 TORONADO, TROFEO

Some 1991 Toronado and Trofeo models equipped with 3800 T.P.I. (VIN L) engine, built prior to vehicle number MU306201, (Federal calibration) or MU306180, (California calibration) may have a condition that prevents the PCM from communicating with the BCM when a diagnostic tool is connected to the vehicle's serial data (ALDL) connector. This condition only occurs when a diagnostic tool is connected to the vehicle's 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.

Axle Scanner Broadcast Service Ratio I.D. Code Part # ------ ------- --------- -------- 3.06 Fed. 1464 AXMU 16162582 3.06 Calif. 1474 AXMW 16162586

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.