Diagnostic System Check - TCM Codes

TCM On-Board Diagnostic (OBD) System Check (1 Of 3):

TCM On-Board Diagnostic (OBD) System Check (2 Of 3):

TCM On-Board Diagnostic (OBD) System Check (3 Of 3):

TCM On-Board Diagnostic (OBD) System Check:

CIRCUIT DESCRIPTION

The Transmission Control Module (TCM) OBD System Check is an organized approach to identifying a problem created by an electronic automatic transmission control system malfunction. It must be the starting point for any transmission electrical diagnosis because it directs the service technician to the next logical step in diagnosing the complaint. Understanding the chart and using it correctly will reduce diagnostic time and prevent the replacement of functioning components.


TEST DESCRIPTION

Numbers below refer to circled numbers on the diagnostic chart.

1. Checks if the "OD/OFF" indicator will light.

2. Checks the TCM's self-diagnostic system for Diagnostic Trouble Codes (DTCs).

3. Checks for any DTCs stored in the ECM through the use of a TECH 1 scan tool.

4. Checks for an open in the self-diagnostic system wiring circuit.

5. Checks for the TCM's ability to ground the "OD/OFF" indicator lamp circuit.

6. Checks for an open "OD/OFF" indicator lamp bulb filament.

7. Determines whether there is an open circuit between the "OD/OFF" lamp circuit and the TCM, or within the Instrument Panel gauge cluster circuitry.

8. Checks for an open wire between the TCM and the Main Relay.

9. Checks for an open wire between the TCM and the Tail Dome fuse.

10. Checks for a poor G103 ground.

11. Checks for a short to ground in wire between the TCM and I/P gauge cluster.

12. Checks for an inoperative OD switch.

13. Checks for a short to ground in wire between the TCM and the OD switch.


DIAGNOSTIC AIDS

Check fuses for opens, and grounds for clean and tight connections.

An intermittent condition may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation.

Check for poor connections at component and inline harness connector terminal for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and for poor terminal-to-wire connections before replacing components. After repairs have been made, repeat the TCM OBD System Check to ensure the system is functioning normally.