TCM Power Relay Control Circuit/Open
P0885 indicates the TCM (Transmission Control Module) power relay control circuit is open or has insufficient voltage supply. The PCM detected that battery voltage is not reaching the TCM properly through its power relay or fuse, preventing normal transmission control operation.
What You Might Notice
- Check Engine Light (MIL) illuminated
- Erratic or delayed transmission shifts
- Transmission stuck in limp mode or fails to shift
- Electronic traction control system disabled
- ABS system disabled or malfunctioning
Most Common Causes
- 1
Blown TCM power relay fuse
The dedicated fuse protecting the TCM power relay circuit has blown, cutting voltage supply to the transmission control module.
- 2
Faulty TCM power relay
The relay that switches power to the TCM has failed internally or stuck open, preventing voltage from reaching the module.
- 3
Corroded or loose wiring connections
Poor connections at the TCM power connector, relay socket, or battery ground can cause voltage drops or open circuits.
- 4
TCM module failure
Internal failure or damage to the Transmission Control Module itself may prevent it from receiving or processing power signals.
How to Diagnose It
- 1
Check Blown TCM power relay fuse — The dedicated fuse protecting the TCM power relay circuit has blown, cutting voltage supply to the transmission control module.
- 2
Check Faulty TCM power relay — The relay that switches power to the TCM has failed internally or stuck open, preventing voltage from reaching the module.
- 3
Check Corroded or loose wiring connections — Poor connections at the TCM power connector, relay socket, or battery ground can cause voltage drops or open circuits.
- 4
Check TCM module failure — Internal failure or damage to the Transmission Control Module itself may prevent it from receiving or processing power signals.
How to Fix It
- 1
Inspect and replace TCM power relay fuse
Locate the TCM power fuse in the vehicle's fuse panel, inspect for blown condition, and replace with the correct amperage rating if blown.
- 2
Test and replace TCM power relay
Use a multimeter to test the relay for continuity; if faulty, remove the relay from the fuse panel and install a new OEM or equivalent replacement.
- 3
Clean and reseat electrical connections
Disconnect the TCM power connector and relay socket, clean contact terminals with electrical contact cleaner, and firmly reconnect to restore voltage supply.
- 4
Replace Transmission Control Module
If relay and fuse are good and connections are clean, the TCM itself may be faulty and require replacement with a new or remanufactured unit.
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