DTC 77 - Pcm Serial Data Line Fault: Notes

DTC 77 will set and TRACTION DISABLED indicator will illuminate if communication between the EBTCM and the IPC is lost. Any condition that will cause a break down in serial communication can set this code. This includes an open, short to ground, or short to voltage on the serial communication line.

NOTE: Test numbers refer to numbers on diagnostic chart. To identify circuits and terminals referenced in text and flowcharts, see WIRING DIAGRAM .

Fig 1: DTC 77 Diagnostic Flow Chart

Courtesy of GENERAL MOTORS CORP.

Checks to see if off-board device can communicate with EBTCM.
Checks for a short to battery voltage in serial data circuit.
Checks for a short to ground in serial data circuit.
Checks for an open in serial data circuit.
Checks if off-board device can communicate with EBTCM.
If connections at EBTCM and DLC connector are okay, replace EBTCM.