P0888 TCM Power Relay Sense Circuit

P0888 points to the TCM power relay sense circuit. The controller is not seeing the expected feedback from the transmission power relay.

Code details

Generic OBD-II · P0

System: Transmission
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not replace the power relay alone without checking the sense circuit; the feedback wire can be the actual fault.

Symptoms of P0888

Harsh, delayed, or slipping shifts, or being stuck in one gear.
Check-engine light, sometimes with limp-home mode.
Flaring RPM or a shudder under load.

Common causes of P0888

Low or degraded transmission fluid.
A failing speed sensor, shift solenoid, or pressure-control circuit.
Wiring, connector, or internal hydraulic/mechanical faults.

Useful checks before replacing parts

Compare relay command, relay output, and relay sense voltage during key-on, cranking, and running conditions.
Inspect relay contacts, fuse feed, sense wire continuity, TCM connector pins, and grounds.
Review companion low/high power input and communication codes that can identify the affected power path.

Related OBD-II codes

These nearby transmission entries can help compare wording and pin down the fault area.