TCM Power Relay Control Circuit/Open
The P0885 code indicates that the Transmission Control Module (TCM) has detected an open or malfunction in the power relay control circuit. This relay supplies voltage to the TCM; when the circuit is open, the TCM may lose power, causing transmission shifting issues, limp mode, or no start conditions. The problem often stems from a faulty relay, blown fuse, wiring damage, or a failing TCM.
01. Most Common Causes
- Blown TCM power relay fuse
- Faulty TCM power relay
- Damaged or corroded wiring/connectors in the relay circuit
- Failing TCM (internal short or open)
02. Symptoms You Will Notice
- Transmission stuck in limp mode (e.g., only 2nd gear)
- Harsh or erratic shifting
- Check Engine Light illuminated
- Vehicle may not start or crank
03. Step-by-Step Diagnosis
Step 1: Check for blown fuses related to the TCM power relay; replace if necessary.
Step 2: Test the TCM power relay for proper operation (coil resistance and switching).
Step 3: Inspect wiring and connectors for damage, corrosion, or loose connections.
Step 4: If all else is good, test TCM power and ground circuits; consider TCM replacement.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
No, it is not safe. The transmission may enter limp mode, causing reduced power and unsafe driving conditions. Have it diagnosed immediately.
How much does it cost to fix?▼
Typically $50-$150 for relay/fuse replacement, but could be higher if wiring repairs or TCM replacement is needed.