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DTC codes / P08xx · Transmission / P0813

P0813Reverse Output Circuit

P0813 indicates that the transmission control module (TCM) has detected an open circuit, short to ground, or short to power in the reverse output circuit, which typically controls the reverse lockout solenoid or reverse lamp relay. The TCM commands the reverse function and monitors the circuit for expected voltage or current, setting the code when the feedback does not match the command.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaTransmission

Symptoms you may notice

  • The check engine light or transmission warning light is illuminated.
  • The reverse lights may not illuminate when the gear selector is placed in reverse.
  • The reverse lockout solenoid may not engage, allowing unintended engagement of reverse gear.
  • The vehicle may be unable to shift into reverse or may shift harshly.
  • Often no symptoms besides the warning light, especially if the fault is intermittent.

Common causes, most likely first

  1. Damaged or corroded wiring harness in the reverse output circuit.
  2. Failed reverse lockout solenoid or reverse lamp relay.
  3. Blown fuse or poor connection at the fuse box.
  4. Faulty transmission control module (TCM) or body control module (BCM) driver.
  5. Water intrusion or corrosion at connectors.
  6. Aftermarket accessories tapped into the reverse circuit.

How to diagnose and fix it

  1. Verify the code with a scan tool and check for related codes in other modules.
  2. Inspect the reverse lamp circuit and lockout solenoid wiring for obvious damage or corrosion.
  3. Test the reverse lockout solenoid and relay for proper resistance and operation.
  4. Check the fuse and ensure power and ground are present at the solenoid connector.
  5. Perform a voltage drop test on the circuit while commanding reverse to identify high resistance.
  6. If the circuit tests good, suspect the TCM or BCM and follow manufacturer diagnostic procedures.

Reverse circuit faults often misdiagnosed

  • A faulty reverse lamp bulb or aftermarket LED conversion can cause this code by altering the circuit's current draw.
  • The reverse output circuit may share a ground with other components, so a bad ground can set P0813 without any reverse-specific symptoms.
  • On some vehicles, the reverse lockout solenoid is part of the shifter assembly and is not serviceable separately, leading to unnecessary transmission repairs.
  • Intermittent P0813 codes often result from chafed wiring near the shifter or under the console, which can be missed during a quick visual inspection.
  • A scan tool that can command the reverse solenoid on and off is essential to confirm the circuit's integrity before replacing parts.

Can I keep driving with P0813?

If the reverse lights are inoperative or the lockout solenoid is not functioning, avoid driving because reverse gear may be difficult to engage or the vehicle may not comply with safety regulations. If only the warning light is on and reverse works normally, you can drive cautiously to a repair shop, but avoid relying on reverse until diagnosed.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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