P0813 – Reverse Output Circuit

System: Powertrain | Standard: ISO/SAE Controlled | Fault type: Circuit

Definition source: SAE J2012/J2012DA (industry standard)

P0813 is a powertrain diagnostic trouble code that indicates a problem detected in the Reverse Output Circuit. In practical terms, the control module has determined that the electrical circuit used to command, signal, or report the reverse output function is not behaving as expected. The reverse output may be used to inform other modules, drive a reverse-related output, or validate reverse selection depending on vehicle design. Because implementations vary by vehicle, the exact circuit routing, connectors, and the monitored conditions can differ. Always confirm the circuit description, pinouts, and test specifications in the applicable service information before testing or replacing parts.

What Does P0813 Mean?

P0813 means the vehicle’s control module has identified a fault in the Reverse Output Circuit. The official definition is strictly “Reverse Output Circuit,” which indicates the issue is electrical and circuit-related rather than a guaranteed mechanical failure. SAE J2012 defines how the DTC is structured and categorized, but the precise logic used to set the code (such as which inputs are compared, how long the fault must be present, and what operating conditions must be met) varies by vehicle. Diagnose P0813 by focusing on the integrity of the reverse output signal path—wiring, connectors, related switches/sensors or drivers, and the module’s ability to command and detect the circuit state.

Quick Reference

• Subsystem: Reverse output circuit (reverse command/status output path between control module and associated electrical load or receiving module).
• Common triggers: Open/shorted wiring, poor connector contact, incorrect circuit state feedback, or an output driver unable to switch as commanded.
• Likely root-cause buckets: Wiring/connector faults, power/ground issues for the circuit, failed switch/sensor (where used), failed output load, or a control module driver/logic issue.
• Severity: Typically moderate; may affect reverse indication/operation and can create safety concerns if reverse signaling is incorrect.
• First checks: Verify reverse-related functions, check for companion DTCs, inspect connectors/harness routing, and confirm fuses/feeds tied to the reverse output circuit.
• Common mistakes: Replacing transmission components or modules before proving the circuit fault with basic electrical tests.

Theory of Operation

The reverse output circuit is an electrical path used to provide a reverse-related output signal. Depending on vehicle design, the control module may command an output driver (such as a transistorized low-side or high-side switch) or pass along a conditioned reverse status signal to other modules. The circuit may be used to drive an output, enable related functions, or communicate reverse state for coordination across systems. The module expects the circuit to transition to the correct state when reverse is requested and to remain stable while reverse is active.

P0813 sets when the module detects the reverse output circuit is not responding correctly—such as a mismatch between the commanded state and the observed circuit condition, or an electrical fault that prevents the circuit from changing state. Monitoring can include internal driver diagnostics and external feedback depending on the platform.

Symptoms

• Warning light MIL/Check Engine light illuminated.
• Reverse indicator Incorrect or intermittent reverse indication on the instrument cluster (varies by vehicle).
• Reverse function Reverse-related features may not activate, activate late, or behave inconsistently (varies by vehicle).
• Intermittent behavior Symptoms may appear only during vibration, moisture exposure, or after recent repairs.
• Shift-related complaints Driver may report reverse engagement concerns that are electrical/indicator-related rather than mechanical (varies by vehicle).
• Additional DTCs Other transmission/communication or electrical circuit codes may be stored alongside P0813.

Common Causes

• Open circuit, short-to-ground, or short-to-power in the reverse output signal wire between the control module and the reverse output load/relay (routing and endpoints vary by vehicle)
• Loose, spread, corroded, or contaminated connector terminals at the control module, transmission range/gear-position interface, reverse lamp relay, or harness junctions
• High resistance in the reverse output circuit due to damaged wiring, poor splices, pin fit issues, or partially broken conductors (intermittent opens)
• Reverse output relay faults (if used) such as a stuck contact, open coil, internal short, or incorrect relay seating causing abnormal circuit behavior
• Failure of the reverse output load (varies by vehicle), such as an open bulb/LED driver module, failed reverse lamp assembly electronics, or an open load path that alters expected circuit feedback
• Power feed or ground problems affecting the reverse output circuit, including poor chassis grounds, shared ground faults, or fuse/fusible-link issues supplying the output stage
• Module output driver fault or internal module issue affecting the ability to command or monitor the reverse output circuit (after wiring and loads are proven good)
• Water intrusion or physical damage in harness runs near underbody, transmission area, tail lamp area, or bulkhead pass-throughs leading to shorts or intermittent connections

Diagnosis Steps

Tools typically needed include a scan tool capable of reading DTCs, freeze-frame data, and live data; a digital multimeter; a test light appropriate for automotive circuits; and back-probing tools. A wiring diagram and connector views from the correct service information are important because the reverse output architecture varies by vehicle (direct drive, relay-controlled, or module-to-module signaling).

1. Confirm the code and capture data. Verify P0813 is current. Record freeze-frame and any companion DTCs, especially those related to gear position/range, output drivers, or power/ground. Clear codes and see if P0813 resets immediately or only after a specific action.
2. Recreate the enabling conditions. Using live data (where available), monitor gear/range status and any parameters indicating reverse command/output state. Attempt to reproduce the fault by shifting into and out of reverse under safe conditions while logging data.
3. Perform a quick visual inspection. Inspect accessible harness sections and connectors associated with the reverse output circuit (locations vary by vehicle). Look for chafing, crushed wiring, pulled pins, corrosion, moisture, or recent repairs. Correct obvious issues before deeper testing.
4. Check related power supply and protection. Inspect fuses, fusible links, and relay power feeds that supply the reverse output circuit or its control path. If any are open, do not replace blindly—inspect the circuit for shorts first and confirm the reason for failure.
5. Verify reverse command vs. actual output behavior. If the scan tool provides a reverse command/request PID and an output/feedback PID, compare them while selecting reverse. A mismatch suggests a circuit/driver/feedback issue; a missing or unstable reverse request may shift attention toward the gear-position/range information pathway (design dependent).
6. Test the reverse output circuit for opens and shorts. With the circuit safely isolated as required by service information, check continuity from the module output to the downstream component/relay. Then check for shorts to ground and shorts to power on the signal wire. Repair wiring faults found, paying attention to areas with movement or heat exposure.
7. Check connector integrity and perform a wiggle test. While observing live data and/or a meter reading, gently wiggle harness segments and connectors related to the reverse output circuit. Intermittent drops, spikes, or state changes point to poor terminal tension, broken conductors, or connector contamination.
8. Load-test the circuit and perform voltage-drop testing. Command reverse (or activate an output test if supported) and measure voltage drop across power and ground paths feeding the reverse output load/relay. Excessive drop indicates high resistance in wiring, connections, grounds, or power feeds. Use service information for acceptable limits and test points.
9. Evaluate the relay and load (if equipped). If a relay is used, verify the control side operates correctly and the switched side passes current without abnormal resistance. Confirm the downstream load is not open or shorted and that its ground is solid. Substitute with a known-good relay only after verifying the circuit is correctly wired and powered.
10. Assess the module driver only after circuit proof. If wiring, connectors, power/ground, relay (if used), and load test good, then consider a control module output driver or internal monitoring fault. Follow service information for any module pin tests, bidirectional output tests, and required confirmations before replacement or reprogramming.

Professional tip: Intermittent P0813 complaints are often connection-related. If the code only appears during shifts into reverse or when the vehicle is moving, prioritize terminal tension checks, harness strain points, and voltage-drop testing under load. A circuit can pass continuity checks yet fail under current demand due to high resistance at a single pin, splice, or ground.

Possible Fixes & Repair Costs

Repair cost for P0813 can vary widely because the reverse output circuit design, access to components, and the actual fault location differ by vehicle. Costs depend on whether the issue is wiring-related, a switch/sensor problem, or a control-module output/communication concern.

• Repair wiring/connector issues: Restore damaged conductors, correct pin fit, remove corrosion, and secure routing to prevent chafing in the reverse output circuit.
• Clean and reseat connectors: Disconnect, inspect, clean as appropriate, and properly reseat terminals at the transmission range sensor/switch, harness junctions, and the controlling module.
• Replace a faulty reverse switch/range sensor: If testing confirms the reverse position input/output path is not switching correctly, replace the verified failed component and perform any required initialization.
• Repair power/ground feeds: Restore missing feeds or poor grounds that affect the module’s ability to drive or sense the reverse output circuit.
• Replace the affected actuator/load: If the reverse output circuit drives an external load (varies by vehicle) and the load is shorted or internally open, replace the verified failed load.
• Module repair or replacement: If all circuit testing is normal but the module cannot drive or interpret the reverse output circuit correctly, follow service information for module diagnostics and replacement procedures.
• Software update/relearn: When service information calls for it after repairs, perform required re-learn or configuration steps to ensure proper reverse output operation.

Can I Still Drive With P0813?

You may be able to drive with P0813, but use caution because reverse-related functions can be affected (varies by vehicle), such as reverse indication, starting interlocks, or other powertrain logic tied to reverse status. If you have any safety-critical symptoms (no-start, unexpected gear indication, warning lamps related to shifting, reduced power, or brake/steering warnings), do not continue driving. Verify reverse operation in a safe area, avoid tight maneuvers if the reverse indication is unreliable, and prioritize diagnosis using the correct service information for your vehicle.

What Happens If You Ignore P0813?

Ignoring P0813 can lead to persistent warning lamps, unreliable reverse indication/output behavior, and intermittent drivability or shifting-related issues depending on how the reverse output circuit is used on your platform. Over time, an electrical fault such as corrosion or harness damage can worsen, potentially causing additional circuit faults, repeated stalls/no-start events on some designs, or damage to connectors and wiring if overheating or shorting is present.

Related Reverse Output Codes

Compare nearby reverse output trouble codes with similar definitions, fault patterns, and diagnostic paths.

• P0812 – Reverse Input Circuit
• P0801 – Reverse Inhibit Control Circuit
• P0720 – Output Speed Sensor Circuit
• P0656 – Fuel Level Output Circuit
• P0888 – TCM Power Relay Sense Circuit
• P0818 – Driveline Disconnect Switch Input Circuit

Key Takeaways

• P0813 is a circuit fault: It indicates a detected problem in the reverse output circuit, not a confirmed mechanical transmission failure.
• Design varies by vehicle: The reverse output circuit may involve a module output, a switch/range sensor, wiring, and a load that depends on platform architecture.
• Start with wiring and connectors: Many root causes are harness damage, poor terminal tension, corrosion, or poor grounds/feeds.
• Test before replacing parts: Confirm the fault with inspection and electrical testing rather than guessing at switches, sensors, or modules.
• Safety comes first: If reverse indication or shifting logic is unreliable, limit driving and diagnose promptly.

Vehicles Commonly Affected by P0813

• Vehicles with electronically controlled automatic transmissions: Where modules monitor or command reverse status through a dedicated circuit.
• Vehicles using a transmission range sensor: Where reverse selection is reported electrically rather than by a purely mechanical linkage.
• Vehicles with integrated powertrain control strategies: Where reverse status is shared across modules for torque, idle, or shift scheduling (varies by vehicle).
• Vehicles with external reverse-related loads: Where a circuit may drive an indicator, relay, or other device tied to reverse operation (varies by vehicle).
• Vehicles with high harness exposure: Underbody harness routing that is more vulnerable to chafing, moisture intrusion, or connector contamination.
• Vehicles with recent transmission or harness service: Where connector seating, pin damage, or incorrect routing can introduce circuit issues.
• Vehicles operated in harsh environments: Frequent water, road debris, or corrosive exposure increasing the likelihood of terminal and wiring problems.

FAQ

Is P0813 telling me the transmission is bad?

No. P0813 indicates the control system detected a problem in the reverse output circuit. The code points to an electrical/signal issue until testing proves a specific component failure or a mechanical condition that caused the circuit to behave abnormally.

Can a wiring problem alone set P0813?

Yes. Harness damage, poor terminal tension, corrosion, or a short/open in the reverse output circuit can trigger P0813. That is why visual inspection and circuit testing should come before replacing switches, sensors, or modules.

Will P0813 affect reverse lights or reverse indication?

It can, depending on vehicle design. Some platforms use the reverse output circuit to drive or report reverse status to other systems, which may impact reverse indication, reverse-related outputs, or logic that relies on knowing when reverse is selected.

What should I check first for P0813?

Start with the basics: confirm the concern, scan for related codes, then inspect the reverse output circuit wiring and connectors for damage, contamination, and poor pin fit. Next, verify power and ground integrity and confirm the circuit switches/outputs correctly using the proper service information for your vehicle.

Can a control module be the cause of P0813?

It is possible, but it should be considered after verifying the circuit, connectors, power/ground, and any involved switch/range sensor or load. If the wiring and components test good yet the module cannot correctly drive or interpret the reverse output circuit, follow service information for module-level diagnostics.

After repairs, clear the code and verify the reverse output circuit operates correctly during a controlled road test and by rechecking for returning faults.