P1768 (15) - Relay Output Always Off

Name of Code:
P1768 (15) - Relay Output Always Off Continuously

Set Condition:
This code is set when less than 3 volts are present at the transmission control relay output (pins 16,17 and 36) circuits at the Transmission Control Module (TCM) when the TCM is energizing the relay.

Theory of Operation:
The Transmission Control Relay is used to supply power to the solenoids and pressure switches when the transmission is in normal operating mode. The relay output is fed back to the TCM through pins 16, 17, and 36. It is referred to as Transmission Control Relay Output". This circuit does not supply power to the TCM, it is only a sense circuit. When the relay is off, no power is supplied to the solenoids and pressure switches, and the transmission is in "limp-in" or "default" mode.

After a controller reset (ignition key turned to the "run" position or after cranking engine), the controller energizes the relay. Prior to this the TCM verifies that the contacts are open by checking for no voltage at the switched battery terminals. After the relay is energized, the TCM monitors the terminals to verify that the voltage is greater than 3 volts.

Transmission Effects:
The MIL will illuminate and the transmission system will default to the Immediate Shutdown routine.

Possible Causes:
- Relay (intermittent relay function caused by oxidized or contaminated relay contacts)
- Short to ground or open circuit in the transmission control relay output circuit(s)
- TCM connector problem
- Relay connector problem
- Relay Ground circuit
- TCM Ground circuit(s)
- TCM