TCM Power Relay Sense Circuit Low
The P0890 code indicates that the Transmission Control Module (TCM) has detected a low voltage condition on the power relay sense circuit. This circuit monitors the voltage supplied to the TCM via the transmission control relay. When the voltage is below the expected threshold (typically less than 10.5 volts), the TCM sets this code. This can be caused by a faulty relay, wiring issues, poor ground connections, or a weak battery/charging system.
1. Symptoms You Will Notice
- Check Engine Light illuminated
- Transmission may shift harshly or erratically
- Transmission may go into limp mode
- No start condition (if relay controls main power)
2. Most Common Causes
- Faulty transmission control relay
- Open or shorted wiring in the relay sense circuit
- Poor ground connection at TCM or relay
- Weak battery or failing alternator
- Corroded or loose relay socket terminals
3. Step-by-Step Diagnosis
Step 1: Scan for additional codes and check freeze frame data.
Step 2: Inspect the transmission control relay and its socket for corrosion or damage.
Step 3: Test relay coil resistance and switching operation with a multimeter.
Step 4: Check voltage at the TCM power relay sense pin (should be battery voltage with key on).
Step 5: Verify battery voltage and alternator output (12.6V+ engine off, 13.5-14.5V running).
Step 6: Inspect wiring and grounds for the TCM and relay circuit.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended. Low voltage can cause erratic transmission behavior and may leave you stranded. Have it diagnosed promptly.
How much does it cost to fix?▼
Typically $50-$150 for relay replacement or minor wiring repair. If the TCM is faulty, costs can exceed $500.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.