TCM Power Relay Sense Circuit High
The P0891 code indicates that the Transmission Control Module (TCM) has detected a voltage higher than expected on the power relay sense circuit. This circuit monitors the voltage supplied to the TCM from the transmission control relay. A high voltage reading can be caused by a faulty relay, wiring issues, or a problem with the TCM itself. This condition can lead to erratic transmission behavior or failure to shift properly.
1. Symptoms You Will Notice
- Check Engine Light illuminated
- Transmission shifting erratically or stuck in gear
- Transmission may go into limp mode
- No start condition in some cases
2. Most Common Causes
- Faulty transmission control relay
- Short to voltage in the sense circuit wiring
- Corroded or damaged connectors
- Faulty TCM
3. Step-by-Step Diagnosis
Step 1: Scan for additional codes and document freeze frame data.
Step 2: Visually inspect the transmission control relay and its wiring for damage or corrosion.
Step 3: Test the relay and sense circuit voltage with a multimeter; compare to manufacturer specs.
Step 4: Check for shorts to voltage or ground in the wiring harness.
Step 5: If all else is fine, test the TCM for proper operation or replace if necessary.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive with this code as it can cause unpredictable transmission behavior, potentially leading to unsafe driving conditions or further damage.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for diagnosis and repair, but can be higher if the TCM needs replacement.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.