P0813: Reverse Output Circuit Malfunction
The P0813 code indicates a fault in the reverse output circuit, which is responsible for signaling the transmission control module (TCM) or powertrain control module (PCM) that the reverse gear is engaged. This circuit typically involves a switch or sensor on the transmission that sends a voltage signal when reverse is selected. A malfunction can be caused by a faulty reverse switch, damaged wiring, a blown fuse, or a problem within the TCM/PCM. When this code is set, the vehicle may not recognize reverse gear, affecting backup lights, reverse lockout, or transmission operation.
1. Symptoms You Will Notice
- Reverse lights not working
- Transmission may not engage reverse gear
- Check Engine Light or Transmission Warning Light illuminated
- Vehicle may not start in reverse or shift out of park
2. Most Common Causes
- Faulty reverse switch/sensor
- Damaged or corroded wiring/connectors in the reverse circuit
- Blown fuse or relay for reverse circuit
- Faulty transmission control module (TCM) or powertrain control module (PCM)
3. Step-by-Step Diagnosis
Step 1: Use an OBD2 scanner to confirm the code and check for additional codes.
Step 2: Visually inspect the reverse switch and wiring for damage, corrosion, or loose connections.
Step 3: Test the reverse switch with a multimeter for continuity when reverse is engaged.
Step 4: Check the fuse and relay for the reverse circuit; replace if blown.
Step 5: If all else is fine, test the signal at the TCM/PCM to determine if the module is faulty.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive with this code, as the vehicle may not properly engage reverse, leading to potential safety hazards or transmission damage.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for parts and labor, depending on the cause. A simple switch replacement is on the lower end, while wiring repairs or module replacement can be higher.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.