Scan Tool - Loss of Communication With Controller

NUMBER: 93-T-16

CORP.REF.NO: 277146

DATE: November 1992

SECTION: 6E, 7A, 4L60-E

SUBJECT:
SCAN TOOL LOSS OF COMMUNICATION

MODELS/YEARS:
1993 BRAVADA

Some 1993 Bravadas 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

^ The screen to flash
^ The screen to display:
- "WAITING FOR DATA"
- "NO DATA. Reselect or turnoff and check Data Link Connector."
^ The control commands not to operate properly.
^ 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 1st, 2nd, 3rd and 4th gears are allowed
- D3 1st, 2nd, and 3rd gears are allowed
- D2 1st and 2nd gears are allowed
- D1 1st and 2nd gears are allowed

^ If current Diagnostic Trouble Codes 24 and 72 are set, only 2nd gear is allowed.
^ If current Diagnostic Trouble Codes 81 and 66 are set, only 3rd gear is allowed.

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

CORRECTION:
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.