P0812
Reverse Input Circuit
- Severity
- Medium
- Driving
- Drivable — book it in
A fault in the reverse input circuit, which tells the module that reverse has been selected. Depending on which way the fault goes, reverse may not engage, may engage when it should not, or may engage without the rest of the car knowing about it - so reversing lamps, parking sensors and the reversing camera can all fail to come on.
Possible causes
- CommonFailed or misadjusted reverse switch, or the transmission range sensor
- CommonWiring or connector fault on the circuit
- CommonCorroded connector at the transmission - it sits low and takes road spray
- PossibleBlown fuse on the reversing lamp circuit
- PossibleFailed reverse inhibit solenoid on vehicles that use one
- PossibleAftermarket parking sensors or a camera spliced into the circuit
What you might notice
- Reversing lamps not working, or staying on
- Reversing camera or parking sensors not activating
- Reverse will not engage
- Reverse engaging harshly
- Check engine light on
What to check, in order
- Check whether the reversing lamps work with reverse selected. This one observation separates a switch or wiring fault from a transmission problem, with no tools.
- Watch the selected gear on the live data screen while selecting reverse.
- Check the transmission range sensor adjustment - it reports reverse on most vehicles, so a sensor fault produces this code too.
- Inspect the connector at the transmission for corrosion.
- Ask whether aftermarket parking sensors, a camera or a tow bar have been fitted. These are commonly spliced into the reverse circuit.
- If reverse itself will not engage, check the fluid level and condition before assuming an electrical fault.
Read this code from your own car
Plug an ELM327 adapter into the OBD-II port under the dashboard. Pin16 reads every stored, pending and permanent code, explains each one like this page does — offline, with no account — and shows what the car recorded when the fault was set.
Where this code sits
P00xxP01xxP02xxP03xxP04xxP05xxP06xxP07xxP08xxP09xxP0AxxP0BxxP0CxxP0DxxP0ExxP0FxxP10xxP11xxP12xxP13xxP14xxP15xxP16xxP17xxP18xxP19xxP1AxxP1BxxP1CxxP1DxxP1ExxP1FxxP20xxP21xxP22xxP23xxP24xxP25xxP26xxP27xxP28xxP29xxP2AxxP2BxxP2CxxP2DxxP2ExxP2FxxP30xxP31xxP32xxP33xxP34xxP35xxP36xxP37xxP38xxP39xxP3AxxP3BxxP3CxxP3DxxP3ExxP3Fxx
Transmission
P0800P0801P0802P0803P0804P0805P0806P0807P0808P0809P0810P0811P0812P0813P0814P0815P0816P0817P0818P0819P0820P0821P0822P0823P0824P0825P0826P0827P0828P0829P0830P0831P0832P0833P0834P0835P0836P0837P0838P0839P0840P0841P0842P0843P0844P0845P0846P0847P0848P0849P0850P0851P0852P0853P0854P0855P0856P0857P0858P0859P0860P0861P0862P0863P0864P0865P0866P0867P0868P0869P0870P0871P0872P0873P0874P0875P0876P0877P0878P0879P0880P0881P0882P0883P0884P0885P0886P0887P0888P0889P0890P0891P0892P0893P0894P0895P0896P0897P0898P0899