TCM Power Relay Control Circuit High
P0887 indicates the transmission control module (TCM) power relay control circuit is detecting abnormally high voltage. This occurs when the PCM detects insufficient or excessive voltage supplied to the TCM through its power relay, preventing proper transmission control and shifting.
What You Might Notice
- Check Engine Light (MIL) illumination
- Erratic or delayed transmission shift patterns
- Transmission failure to shift gears properly
- Electronic traction control disabled or inoperative
- ABS system disabled or malfunctioning
Most Common Causes
- 1
Bad TCM power relay
The relay controlling power to the TCM may be stuck closed or delivering excessive voltage, causing the control circuit to register high voltage.
- 2
Blown or loose TCM fuse
A damaged fuse or poor fuse contact prevents proper voltage regulation to the TCM, triggering the code.
- 3
Corroded or damaged wiring/connectors
Corrosion, fraying, or loose connections in the TCM power circuit can cause voltage irregularities and high voltage conditions.
- 4
TCM or PCM electrical malfunction
Internal failure within the transmission control module or powertrain control module can cause voltage detection errors.
How to Diagnose It
- 1
Check Bad TCM power relay — The relay controlling power to the TCM may be stuck closed or delivering excessive voltage, causing the control circuit to register high voltage.
- 2
Check Blown or loose TCM fuse — A damaged fuse or poor fuse contact prevents proper voltage regulation to the TCM, triggering the code.
- 3
Check Corroded or damaged wiring/connectors — Corrosion, fraying, or loose connections in the TCM power circuit can cause voltage irregularities and high voltage conditions.
- 4
Check TCM or PCM electrical malfunction — Internal failure within the transmission control module or powertrain control module can cause voltage detection errors.
How to Fix It
- 1
Test and replace TCM power relay
Use a multimeter to test the relay for proper operation. If faulty, replace with a new OEM-equivalent relay to restore correct voltage control.
- 2
Inspect and replace TCM fuse
Check the TCM fuse for blown condition and verify fuse rating matches specification. Replace if damaged and ensure fuse holder contacts are clean.
- 3
Repair wiring and connectors
Inspect all wiring between battery, relay, fuse, and TCM for corrosion, damage, or loose connections. Clean corroded contacts and repair or replace damaged wiring.
- 4
Replace TCM if electrical testing passes
If relay, fuse, and wiring test normal, the TCM itself may be faulty. Consult service manual for proper replacement and reprogramming procedures.
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