P0813 Reverse Output Circuit Malfunction

The P0813 trouble code is an OBD-II diagnostic trouble code related to the reverse output circuit of an electronically controlled transmission.

P0813 – Reverse Output Circuit Malfunction

This code means that the transmission control system has detected a problem with the electrical circuit responsible for controlling or monitoring the reverse-gear output signal.

In a typical system, when the driver selects Reverse (R), the transmission control module (TCM), powertrain control module (PCM), body control module (BCM), or another control unit sends the appropriate signal to activate functions associated with reverse operation.

If the expected electrical signal is missing, incorrect, or outside the specified range, the control module may store P0813.

What Does P0813 Mean?

A simplified reverse-control system can be represented as:

Gear selector → Transmission range sensor → TCM → Reverse output circuit → Reverse-related system

Depending on the vehicle, this output can be used for:

• Reverse lamps

• Reverse relay

• Body control module

• Parking sensors

• Rear-view camera activation

• Transmission control

• Other vehicle systems

The exact architecture varies considerably between manufacturers.

P0813 is therefore an electrical output-circuit fault. It does not automatically mean that the transmission's reverse gear itself is mechanically damaged.

What Is the Reverse Output Circuit?

The reverse output circuit is an electronically controlled signal associated with selecting Reverse.

When the driver selects R, the control system needs to recognize the request and activate the appropriate output.

A simplified sequence is:

Selector in R → Range information recognized → Control module commands reverse output → Reverse-related systems activated

If the control module detects that the output circuit does not behave as expected, P0813 can be stored.

Symptoms of P0813

Possible symptoms include:

• Check Engine Light

• Transmission warning light

• Reverse gear not engaging

• Delayed Reverse engagement

• Reverse lamps not working

• Reverse lamps staying on

• Rear parking sensors not activating

• Rear camera not activating

• Incorrect gear indication

• Transmission entering limp mode

• Intermittent Reverse operation

• Gear selector problems

The exact symptoms depend on what part of the reverse-output system is affected.

Common Causes of P0813

Faulty transmission range sensor

The control module may not correctly recognize that Reverse has been selected.

Faulty gear selector

An electronic selector may fail to send the correct Reverse position information.

Damaged reverse output wiring

An open, shorted or damaged wire can prevent the output signal from reaching the relevant component.

Loose connector

A loose terminal can create an intermittent electrical connection.

Corroded connector

Moisture and corrosion can increase resistance or interrupt the circuit.

Blown fuse

A fuse associated with the reverse output circuit may be open.

Faulty relay

Some vehicles use a relay to control reverse-related circuits.

Short to ground

A signal wire contacting ground can produce an abnormal output.

Short to power

Unwanted voltage can also cause an output-circuit malfunction.

Faulty reverse lamp circuit

A short or open circuit in the reverse-light wiring can sometimes be involved.

Faulty control module

A TCM, PCM or BCM can potentially cause the fault, although module failure should not be assumed before the circuit is tested.

CAN communication problem

On modern vehicles, the TCM may send the Reverse status to another module through the CAN network instead of directly controlling every reverse-related function.

Low system voltage

A weak battery or charging problem can affect electronically controlled outputs.

Is P0813 Serious?

P0813 can range from a relatively minor electrical problem to a significant transmission-control problem.

If only the reverse lamps or another auxiliary reverse function is affected, the vehicle may still drive normally.

However, if Reverse itself does not engage, the problem becomes considerably more important.

Loss of Reverse can make the vehicle difficult or impossible to maneuver safely.

Can You Drive With P0813?

If Reverse still operates normally and the problem is limited to an auxiliary function such as the reverse lamps, the vehicle may be driven carefully to a repair facility.

However, if:

• Reverse does not engage

• Reverse engagement is severely delayed

• The transmission enters limp mode

• The vehicle shifts unpredictably

• Reverse lamps remain permanently illuminated

the vehicle should be inspected promptly.

A vehicle without functioning reverse lamps can also present a safety issue, particularly in low-light conditions.

P0813 and Reverse Gear

It is important to distinguish between an electrical Reverse output problem and a mechanical failure of Reverse gear.

P0813 does not automatically mean:

"The reverse gear inside the transmission is broken."

The code concerns the electrical control/output system.

However, if the vehicle also cannot physically move backward, further diagnosis is necessary to determine whether the problem is:

• Electrical

• Hydraulic

• Electronic

• Mechanical

P0813 and Reverse Lights

The reverse-output circuit can be associated with the reverse lamps, depending on the vehicle.

A typical sequence may be:

Transmission in R → Control module recognizes R → Reverse output activated → Reverse lamps turn on

If the reverse lamps do not work, inspect:

• Bulbs

• LEDs

• Fuse

• Wiring

• Connectors

• Relay

• Reverse switch

• Range sensor

• BCM

• TCM

However, not every vehicle uses the same circuit architecture.

P0813 and Rear Camera

On modern vehicles, selecting Reverse often activates the rear-view camera.

The system may work like:

Selector in R → TCM/BCM receives Reverse status → Camera system receives Reverse request → Rear camera activates

If P0813 occurs, the rear camera may fail to activate.

However, a camera that does not work can also have an independent camera, wiring or infotainment-system fault.

How to Diagnose P0813

The diagnosis should determine whether the problem is with the Reverse request, range information, output circuit, wiring, relay, or receiving module.

1. Scan all control modules

Check:

• TCM

• PCM

• BCM

• Instrument cluster

• Parking-assistance module

• Camera module where applicable

Look for additional codes involving:

• Transmission range

• Gear selector

• Reverse switch

• Reverse lamps

• CAN communication

• System voltage

Additional codes can provide an important clue.

2. Check whether Reverse engages

Move the selector to Reverse and determine whether the vehicle actually moves backward.

If Reverse operates normally, the problem may be limited to the electrical output or an auxiliary function.

If Reverse does not engage, the transmission-control system requires further investigation.

3. Check the gear display

Verify that the instrument cluster shows:

R

when Reverse is selected.

If it does not, investigate the range sensor or gear-selector system.

4. Monitor live data

Use a diagnostic scanner to monitor:

• Transmission range

• Reverse status

• Reverse request

• Reverse output

• Gear selector position

Select Reverse and check whether the control module recognizes it.

5. Check the reverse output

Where supported, determine whether the control module is actually commanding the Reverse output.

This can help separate:

Control-module problem

from:

Wiring/output problem

6. Inspect the fuse

Check fuses associated with:

• Reverse lamps

• Transmission control

• BCM

• TCM

• Gear selector

Do not repeatedly replace a blown fuse without identifying why it failed.

7. Inspect the relay

If the vehicle uses a reverse-related relay, test:

• Relay coil

• Relay contacts

• Power supply

• Control signal

8. Inspect wiring

Look for:

• Broken wires

• Chafing

• Pinched wiring

• Melted insulation

• Corrosion

• Poor previous repairs

9. Inspect connectors

Pay attention to:

• Loose terminals

• Bent pins

• Corrosion

• Water intrusion

• Damaged locking mechanisms

10. Test the transmission range sensor

Verify that the sensor correctly identifies:

P → R → N → D

If Reverse is not recognized correctly, the range sensor or selector becomes a major suspect.

11. Check the Reverse switch where equipped

Some vehicles use a dedicated reverse switch rather than relying entirely on a transmission range sensor.

Test the switch according to the manufacturer's specifications.

12. Check the output voltage

If the control module commands the reverse output but the receiving circuit does not activate, measure the output circuit.

Check for:

• Correct voltage

• Continuity

• Short to ground

• Short to power

13. Check CAN communication

If the Reverse signal is transmitted between modules, verify communication.

For example:

TCM recognizes R → CAN communication → BCM receives R → Reverse output activated

A communication failure can interrupt this sequence.

14. Check battery and charging voltage

Low voltage can cause abnormal operation of multiple control modules.

Check:

• Battery condition

• Charging voltage

• Battery terminals

• Main grounds

Can a Bad Transmission Range Sensor Cause P0813?

Yes.

If the range sensor does not correctly identify Reverse, the control module may never issue the expected Reverse output.

For example:

Selector = R

but:

Range sensor = N

The control system may not activate the reverse output.

Can a Bad Gear Selector Cause P0813?

Yes.

Electronic gear selectors can contain several position sensors.

A selector fault can cause:

• R not recognized

• Incorrect gear display

• Reverse lamps not activating

• Starting problems

• Transmission warnings

Can Wiring Cause P0813?

Yes.

A damaged output wire can prevent the correct signal from reaching the relevant module or component.

Possible wiring problems include:

• Open circuit

• Short to ground

• Short to power

• High resistance

• Corrosion

Intermittent wiring faults can be particularly difficult to identify.

Can P0813 Cause Reverse Not to Work?

It can, depending on the vehicle.

P0813 itself identifies an electrical output-circuit problem, but the affected circuit may be part of the system that controls or confirms Reverse operation.

If Reverse does not engage, additional diagnostics are required to determine whether the cause is:

• Range recognition

• Electronic control

• Solenoid operation

• Hydraulic pressure

• Internal mechanical transmission components

Can P0813 Cause Limp Mode?

Yes, depending on the vehicle and the other faults present.

If the control module cannot reliably determine or control the transmission state, it may activate a protective strategy.

Possible results include:

• Limited gear selection

• Fixed gear

• Manual mode disabled

• Transmission warning

Always check for additional codes.

Can P0813 Cause Reverse Lights to Stay On?

Yes, potentially.

If the reverse output is stuck active or the control system incorrectly believes Reverse is selected, the reverse lamps may remain illuminated.

Possible causes include:

• Shorted wiring

• Faulty range sensor

• Faulty reverse switch

• Stuck relay

• Control-module output problem

Can a Weak Battery Cause P0813?

Yes, potentially.

Low system voltage can affect electronic control modules and output circuits.

If several unrelated electrical codes appear at the same time, check the battery and charging system before replacing transmission components.

Common Diagnostic Mistakes With P0813

Assuming the transmission needs rebuilding

P0813 is an electrical output-circuit code and does not automatically indicate internal transmission failure.

Replacing the range sensor immediately

The problem may be in the output wiring, relay or receiving module.

Replacing the TCM without testing the circuit

The output should be electrically tested before condemning the module.

Ignoring reverse lights

The behavior of the reverse lamps can provide a useful clue.

Ignoring CAN communication

Modern vehicles frequently distribute Reverse information electronically between modules.

Ignoring fuses and relays

A simple power-distribution problem can produce an apparently complex transmission fault.

What Is the Correct Repair for P0813?

The repair depends on the confirmed cause.

Possible repairs include:

• Replacing the transmission range sensor

• Replacing a faulty Reverse switch

• Replacing the gear selector

• Repairing damaged wiring

• Repairing connector terminals

• Cleaning corrosion

• Repairing water intrusion

• Replacing a faulty fuse

• Replacing a faulty relay

• Repairing a short circuit

• Repairing an open circuit

• Repairing CAN communication wiring

• Updating control-module software

• Replacing the TCM or BCM only when confirmed defective

If Reverse itself does not engage, additional transmission-control and mechanical tests may be required.

How to Test the Vehicle After Repair

After repairing P0813, verify that:

• Park is correctly recognized

• Reverse is correctly recognized

• Neutral is correctly recognized

• Drive is correctly recognized

• Reverse engages correctly

• Reverse lamps operate correctly

• Rear camera activates where equipped

• Parking sensors activate where equipped

• Gear display shows R correctly

• Transmission shifts normally

• No warning lights remain

• P0813 does not return

Frequently Asked Questions About P0813

What does P0813 mean?

P0813 means the vehicle has detected a malfunction in the Reverse Output Circuit.

Does P0813 mean the reverse gear is mechanically broken?

No. The code concerns an electrical output circuit. Mechanical transmission failure requires separate diagnosis.

Can P0813 cause Reverse not to work?

Yes, depending on the vehicle's control-system design.

Can P0813 cause reverse lights not to work?

Yes. The reverse output can be involved in controlling the reverse-light circuit on some vehicles.

Can P0813 cause the rear camera not to activate?

Potentially. If the camera relies on the Reverse signal, an output problem can prevent activation.

Can a range sensor cause P0813?

Yes. If Reverse is not correctly recognized, the expected reverse output may not be generated.

Can wiring cause P0813?

Yes. Open, shorted, corroded or damaged wiring can cause the code.

Can P0813 cause limp mode?

It can, depending on the vehicle and other faults.

Final Thoughts on P0813

P0813 – Reverse Output Circuit Malfunction indicates that the vehicle's control system has detected a problem with the electrical output associated with Reverse operation.

The most important areas to investigate are the transmission range sensor, gear selector, Reverse switch, wiring, connectors, fuses, relays and the modules responsible for controlling or receiving the Reverse signal.

The most useful diagnostic question is:

Does the vehicle correctly recognize Reverse, and does the reverse output respond when Reverse is selected?

If the control module does not recognize Reverse, investigate the range sensor or selector.

If the module recognizes Reverse but the output does not operate, investigate the output circuit, wiring, relay or receiving module.

If the electrical system works correctly but the vehicle still cannot move backward, then further transmission hydraulic and mechanical diagnosis is necessary.

Most importantly, P0813 does not automatically mean that the transmission needs to be replaced or rebuilt. A systematic electrical diagnosis should be performed first, because the actual repair may be as simple as a faulty switch, damaged wire, corroded connector, blown fuse or defective relay.