Faulty reverse switch or sensor (gear selector, range sensor or reverse lamp switch, depending on model); Damaged, chafed or corroded wiring in the reverse circuit; Poor connection or water ingress at the switch or control unit connector; Blown fuse or faulty relay supplying the reverse circuit; Selector linkage or cable out of adjustment, so the switch reads the wrong position; Faulty control unit or software fault.

P0813

Reverse Output Circuit.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
8: AreaTransmission
13: FaultThe specific fault in that area

What it means

P0813 is the generic code for a fault in the reverse output circuit. The control unit (usually the transmission control module, or the engine or body control module on some vehicles) monitors the circuit that signals reverse gear is selected. It sets the code when the signal it sees does not match the expected state or is electrically out of range. What this circuit feeds, such as reversing lights, reverse inhibit or the transmission itself, varies by model.

Symptoms

Reversing lights not working or staying on
Gearbox not engaging reverse or hesitating when selecting it
Parking sensors or reversing camera not activating automatically
Warning light on the dashboard, such as the gearbox or engine light
Gearbox stuck in a fallback mode on some automatic models

Possible causes

Faulty reverse switch or sensor (gear selector, range sensor or reverse lamp switch, depending on model)likely
Damaged, chafed or corroded wiring in the reverse circuitlikely
Poor connection or water ingress at the switch or control unit connectorlikely
Blown fuse or faulty relay supplying the reverse circuitpossible
Selector linkage or cable out of adjustment, so the switch reads the wrong positionpossible
Faulty control unit or software faultrare

How to diagnose

Read all stored codes and freeze frame data, and note whether other transmission or lighting faults are present
Check whether the reversing lights work and whether they come on in reverse only
Check the relevant fuse and relay against the wiring diagram for the specific model
Inspect the wiring and connectors at the reverse switch or range sensor for damage, corrosion or water
Using live data, watch the reverse signal status while moving the selector through each position and confirm it changes correctly
Check the selector linkage or cable adjustment and the physical condition of the switch
Test the circuit for supply, earth and signal continuity with a multimeter, following the manufacturer's wiring diagram
Check for software updates or known issues for the model before condemning the control unit

How to fix

Replace the faulty reverse switch or range sensor
Repair or replace damaged wiring and clean or renew corroded connectors
Replace the blown fuse after finding the cause, or replace a faulty relay
Adjust or repair the selector linkage or cable
Update the control unit software only if an outdated version is a known cause for the model, or repair or replace the control unit as a last resort
Clear the code and road test to confirm it does not return

Can I keep driving?

Medium severity

The car can usually be driven short-term, but missing reversing lights are a safety and legal issue, and reverse may not work properly. Get it checked soon, and avoid driving if reverse is unreliable or the gearbox is in a fallback mode.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.