SCAN TOOL LOSS OF COMMUNICATION (INFORMATION)

SUBJECT: SCAN TOOL LOSS OF COMMUNICATION (INFORMATION)

VEHICLES AFFECTED: 1993 "C/K, S/T" TRUCKS AND "M/L, G" VANS WITH 4L60-E TRANSMISSION

APPLICATIONS:

C/K - Trucks Under 8600 GVW S/T - Trucks With 4.3L Non Turbo M/L and G - Vans

CONDITION:

Some 1993 vehicles equipped with a HYDRA-MATIC 4L60-E transmission may have periodic interruptions in communication between the scan tool (TECH 1, T100) and the controller. These interruptions may cause:

T-100/T-50

A momentary pause of data on the screen. The T-100/T-50 will attempt to re-establish communications with the controller. If this is successful, then data will continue to be displayed.

If the attempt to re-establish communication fails, then a LOSS OF COMMUNICATION screen will be displayed.

TECH 1

o The screen to flash

o The screen to display: - "WAITING FOR DATA" - "NO DATA. Reselect or turnoff and check Data Link Connector."

o The control commands not to operate properly.

o The snapshot to trigger during the waiting mode.

In some cases the transmission device control commands may be disregarded by the controller in the following instances:

If the brake switch is applied, the controller will ignore the TCC control commands.

If the "PRNDL SWITCH" indicates: - D4 1 st, 2nd, 3rd and 4th gears are allowed - D3 lst, 2nd, and 3rd gears are allowed - D2 1 st and 2nd gears are allowed - Dl 1 st and 2nd gears are allowed

If current DTC's 24 and 72 are set, only 2nd gear is allowed.

If current DTC's 81 and 66 are set, only 3rd gear is allowed.

This is due to software constraints within the controller. Replacing the PCM controller will not correct the condition.

Usually, the scan tool resumes communication with the controller within 1-5 seconds. If this does not occur, turn the key off, wait 10 seconds, then turn the key on and reselect the scan tool option.

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.