TCM Power Relay Sense Circuit High
P0891 indicates the transmission control module (TCM) is detecting abnormally high voltage in its power relay sense circuit. This electrical fault can result from a faulty relay, wiring issue, or internal TCM malfunction that prevents proper voltage regulation to the transmission control system.
What You Might Notice
- Check engine light illuminated
- Transmission shifting erratically or harshly
- Electronic traction control disabled
- Transmission may fail to shift into certain gears
- ABS system disabled
Most Common Causes
- 1
Bad TCM power relay
The relay controlling power to the TCM may be stuck closed or failing, causing excessive voltage to be sensed on the relay sense circuit.
- 2
Blown fuse in TCM power circuit
A blown fuse can create abnormal voltage conditions in the TCM power supply circuit, triggering the sense circuit fault.
- 3
Wiring damage or corrosion
Damaged, corroded, or loose wiring connections in the TCM power relay sense circuit can cause voltage irregularities and circuit faults.
- 4
Faulty transmission control module
Internal TCM failure or a defective voltage sensing circuit within the module itself may cause it to misreport high voltage conditions.
How to Diagnose It
- 1
Check Bad TCM power relay — The relay controlling power to the TCM may be stuck closed or failing, causing excessive voltage to be sensed on the relay sense circuit.
- 2
Check Blown fuse in TCM power circuit — A blown fuse can create abnormal voltage conditions in the TCM power supply circuit, triggering the sense circuit fault.
- 3
Check Wiring damage or corrosion — Damaged, corroded, or loose wiring connections in the TCM power relay sense circuit can cause voltage irregularities and circuit faults.
- 4
Check Faulty transmission control module — Internal TCM failure or a defective voltage sensing circuit within the module itself may cause it to misreport high voltage conditions.
How to Fix It
- 1
Inspect and test TCM power relay
Test the relay with a multimeter to verify it is functioning correctly. Replace the relay if it is stuck closed, shows continuity when de-energized, or fails resistance tests.
- 2
Check and replace TCM fuse if blown
Locate the TCM power fuse in the fuse box and inspect it for a broken filament. Replace with the correct amperage rating if blown. If it blows again immediately, investigate the circuit for a short.
- 3
Inspect wiring and connections
Check the TCM power relay sense circuit wiring for corrosion, damage, or loose connectors. Clean corroded terminals and repair or replace damaged wiring. Ensure all connectors are fully seated.
- 4
Replace transmission control module
If electrical testing of the relay, fuse, and wiring are all normal, the TCM itself is likely faulty and requires replacement. Have the module reprogrammed to your vehicle after installation.
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