P0888 — TCM Power Relay Sense Circuit

TCM power-relay monitoring: A fault is reported in the named circuit; the definition does not identify which component causes it. Relay control and feedback from the relay output are separate functions. The code does not establish whether the relay, wiring or controller is responsible.

Affected system: Transmission controller electrical supply

Symptoms

• Warning light may illuminate
• Related system function may be impaired
• Vehicle-specific symptoms vary

Possible causes

• Low or unstable supply voltage, fuse or relay fault, poor ground, or wiring damage
• Related wiring, connector, power or ground fault
• Vehicle-specific mechanical or control issue

What to check

• Record stored and pending codes and freeze-frame data
• Measure battery and charging voltage under load and compare with scan data; test the named circuit, fuse, relay, grounds and connectors.
• Confirm measured values against the vehicle service information
• Retest under the conditions that set the code
• Measure battery and charging voltage under load and compare with scan data; test the named circuit, fuse, relay, grounds and connectors.
• Repair the verified cause and confirm the code does not return

Also written as: P0888-00, P088800, PO888 (some scan tools add the fault-type byte, e.g. -00).