P0888: TCM Power Relay Sense Circuit

What it means

The TCM power relay reports a sense circuit 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 feeds the transmission control system, and its sense circuit reports the relay's electrical state back to the TCM. P0888 indicates a fault in that feedback circuit, so the TCM may not be able to confirm the relay output even if the relay is switching.

Common causes

Most likely first.

1. Feedback wire fault
2. Relay contact aged

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

1. Record freeze-frame data and check live relay command and sense readings to see whether the feedback fails during startup, shifting, or another event.
2. Inspect the relay, sense-wire connectors, and harness for corrosion, loose pins, damaged insulation, or a broken feedback wire.
3. Check continuity through the feedback wire and its connections using the vehicle's wiring diagram.
4. Compare the sense-circuit reading with the manufacturer's specification while the relay is commanded on and off.
5. If wiring checks pass, test the relay contacts and TCM sense input using the manufacturer's diagnostic procedure.

Common fixes

• Clean and secure corroded or loose sense-circuit connector pins.
• Repair a broken or damaged relay feedback wire.
• Replace a relay with worn or unreliable contacts.
• Repair the TCM sense input circuit if testing confirms an internal fault.

Can I keep driving?

If shifting remains normal, drive only as needed while monitoring for warning lights or shift changes. Avoid continuing if the vehicle enters limp mode, slips, or shifts harshly, because the TCM may not be receiving reliable relay-status feedback.