P0885 - TCM Power Relay Control Circuit/Open
- Faulty Transmission Control Module (TCM) Power Relay
- Transmission Control Module (TCM) Power Relay harness is open or shorted
- Transmission Control Module (TCM) Power Relay circuit poor electrical connection
- Engine Light ON (or Service Engine Soon Warning Light)
The transmission control relay is used to supply power to the solenoid pack when the transmission is in normal operating mode. When the relay is off, no power is supplied to the solenoid pack and the transmission is in Limp-in mode. The relay output is fed back to the Powertrain Control Module (PCM). It is referred to as the Transmission Control Relay Output circuit or switched battery.
Immediately after a controller reset (ignition key turned to the run position or after cranking engine), the PCM verifies that the relay contacts are open by checking for no voltage at the switched battery terminals. After this is verified, the voltage at the pressure switches is checked. There should be no voltage on the pressure switches at this time. The PCM will then activate the relay.