Reverse Output Circuit
The ECU detected a problem with the reverse gear output signal circuit—the electrical signal telling the transmission or backup lights to engage isn't working correctly. It's like a light switch that's broken and won't send the "on" signal to the lights.
The ECU monitors the reverse output control circuit voltage and current to verify the signal is properly commanding the reverse solenoid or backup light relay. It expects a clean voltage transition when Reverse gear is selected and detects faults when voltage is missing, shorted, or open.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Reverse Output Signal Voltage | 12V when Reverse selected, 0V in other gears | No voltage change, stuck low, or stuck high |
| Reverse Circuit Continuity | < 5 ohms resistance when active | > 10 ohms or open circuit |
Code P0813 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.
Once the fault is repaired, P0813 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.
The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.