DTC 77

DTC 77 PCM Serial Data Line Malfunction






Circuit Description

Code 77 will set and the "TRACTION DISABLED" message will be displayed if the EBTCM and the PCM lose serial communication with each other.

DTC will set when

Any condition that will cause a breakdown in serial communication can set this code. This includes an open, a short to ground or a short to voltage on the serial communication line.

Action Taken

1. Code set.
2. TCS switched "OFF".
3. "TRACTION DISABLED" message displayed.

Test Description

Test numbers refer to circled numbers on the diagnostic chart.

1. This test checks to see if the off-board device can communicate with the EBTCM.
2. This test checks for a short to battery in the serial data circuit.
3. This test checks for a short to ground in the serial data circuit.
4. This test checks for an open in the serial data circuit.
5. This test checks to see if the off-board device can communicate with the EBTCM.
6. Checks the connectors at the EBTCM and DLC for damage or misalignment. If the connectors are OK, the EBTCM is at fault.

Diagnostic Aids

The problem may be intermittent. Try performing the tests shown while "wiggling" wiring and connectors; this can often cause the fault to appear. Also, check the operation of the TECH 1 on another vehicle to ensure it is working properly.

IMPORTANT: Code 77 will never be displayed while serial data fault is current. A current fault would result in a "NO TCS DATA", and "TRACTION DISABLED" messages as well as PCM Code P133.