What it means
The TCM power relay reports a control circuit/open condition. TCM supply control is impaired.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
The TCM power relay switches supply power to the transmission control system, and its control circuit lets the module command or monitor relay operation. P0885 sets when the relay control circuit is open, preventing the expected control signal from being completed.
Common causes
Most likely first.
- Open in coil control wire
- Open relay coil
- Pin pushed back out of connector body
Symptoms
- Check engine or transmission warning light on
- Harsh, delayed, or missing shifts
- Possible limp mode (locked in one gear)
- Slipping or shuddering during gear changes
How to diagnose it
- Save freeze-frame data and check for related TCM power or relay codes to determine whether the module lost supply when the fault set.
- Inspect the TCM power relay, relay socket, and connectors for a missing relay, loose fit, corrosion, or a pushed-back terminal.
- Check the relay coil and control wiring for an open circuit using the manufacturer's service information.
- Verify the control circuit's connections and commanded relay operation with a scan tool or circuit test, following the manufacturer's procedure.
- If the relay and wiring are intact, check the TCM's relay-control output for an open or module-side fault.
Common fixes
- Seat the relay fully and secure loose connections.
- Repair a pushed-back or corroded relay-socket terminal.
- Repair an open relay control wire.
- Replace the relay if its coil is open.
- Repair the TCM relay-control circuit if testing isolates the fault to that circuit.
Can I keep driving?
Avoid driving if the transmission will not shift normally or has entered limp mode, since the relay control fault can interrupt TCM power. Arrange repair before relying on the vehicle for a trip where loss of normal shifting would be unsafe.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.