TCM Power Relay Sense Circuit Malfunction
The P0888 code indicates a problem in the transmission control module (TCM) power relay sense circuit. This circuit monitors the voltage supplied to the TCM via the power relay. When the TCM detects an unexpected voltage level (too high, too low, or absent) on the sense circuit, it sets this code. Common causes include a faulty relay, blown fuse, wiring issues, or a failing TCM. This can lead to transmission shifting problems or no start conditions.
1. Symptoms You Will Notice
- Check Engine Light illuminated
- Transmission shifting erratically or stuck in gear
- Vehicle may not start or crank
- Transmission warning light on
2. Most Common Causes
- Faulty TCM power relay (sulfated contacts or degraded coil)
- Relay sense circuit shorted to ground or voltage
- Relay sense circuit open or high resistance
- Corroded, loose, or damaged connectors/terminals in the sense circuit
- Defective TCM with damaged internal monitoring circuit
- Blown or poor-contact TCM power supply fuse
3. Step-by-Step Diagnosis
Step 1: Use a scan tool to confirm P0888 and check for other codes.
Step 2: Inspect the TCM power relay and fuse; test for power and ground at the relay socket.
Step 3: Check wiring and connectors between the relay, fuse, and TCM for damage or corrosion.
Step 4: If all else is good, test the TCM for proper operation or replace it.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended. The transmission may not shift properly, and the vehicle could stall or fail to start, posing a safety risk.
How much does it cost to fix?▼
Typically $50-$150 for relay/fuse replacement; TCM replacement can cost $500-$1000 or more.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.