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.
01. Most Common Causes
- Faulty transmission control relay
- Short to voltage in the sense circuit wiring
- Corroded or damaged connectors
- Faulty TCM
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Transmission shifting erratically or stuck in gear
- Transmission may go into limp mode
- Possible no-start condition if relay fails completely
03. Step-by-Step Diagnosis
Step 1: Use a scan tool to retrieve all codes and freeze frame data.
Step 2: Inspect the transmission control relay and its wiring for damage, corrosion, or loose connections.
Step 3: Measure voltage at the relay sense circuit with a multimeter; compare to manufacturer specifications.
Step 4: Check for shorts to voltage in the wiring harness between the relay and TCM.
Step 5: If wiring and relay are okay, test the TCM for proper operation or replace if necessary.
04. Commonly Affected Makes
05. 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 to fix P0891 typically ranges from $50 to $150 for a relay replacement, but can be higher if wiring repairs or TCM replacement is needed.