Reverse Input Circuit Malfunction
The P0812 code indicates a problem in the reverse input circuit, which is part of the transmission range sensor or switch. This circuit tells the powertrain control module (PCM) when the transmission is in reverse. A fault can cause incorrect gear detection, affecting reverse lights, backup camera activation, and transmission shift logic. Common causes include a faulty transmission range sensor, wiring issues, or a defective PCM.
01. Most Common Causes
- Faulty transmission range sensor (TRS) or reverse switch
- Damaged, corroded, or loose wiring/connectors in the reverse circuit
- Blown fuse or relay for reverse lights
- Defective PCM (rare)
02. Symptoms You Will Notice
- Reverse lights not working
- Backup camera or parking sensors not activating
- Transmission may not shift into reverse or shift harshly
- Check Engine Light illuminated
03. Step-by-Step Diagnosis
Step 1: Scan for additional codes and verify P0812 is present.
Step 2: Visually inspect wiring and connectors at the transmission range sensor for damage or corrosion.
Step 3: Test the reverse switch/sensor with a multimeter for proper continuity when in reverse.
Step 4: Check fuses and relays related to reverse lights and transmission control.
Step 5: If all else is good, test PCM output signals or consult a professional for further diagnosis.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended. While the vehicle may still drive, the transmission may not shift correctly, and reverse lights/camera may fail, posing a safety risk.
How much does it cost to fix?▼
Typically $50-$150 for diagnosis and repair, but costs can vary if the transmission range sensor needs replacement (parts $30-$100, labor $50-$100).