P0812 code meaning
Reverse Input Circuit
What P0812 means
P0812 concerns the input 'reverse engaged' at the engine or transmission module – the reverse or back-up lamp switch on a manual gearbox, or the R contact of a selector. Modules check it for open or stuck states and against a second source such as a gear position sensor or the direction from speed sensors. A Honda patent describes this double detection: reverse counts only when switch and gear position sensor agree; if only one reports R, it is a fault and engine speed is limited. No manufacturer document with thresholds is available to us. Back-up lamps, reversing camera or parking aids may fail; on automated manual gearboxes reverse may be blocked. CARB lets such safety and comfort inputs run without the MIL.
P0812 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyEasy, DIY possible
- Typical labor0.5 to 1.5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P0812
- Back-up lamps never or always on
- Reversing camera or parking aid does not switch on
- Usually no check engine lamp
Common causes of P0812
- Most likelyReverse or back-up lamp switch faulty or misadjusted
- Most likelyConnector loose or wire broken (e.g. after clutch work)
- PossibleBack-up lamp circuit fuse blown
- Less likelyGear position sensor reporting the wrong position
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Reverse switchSwitch wiringEngine control moduleTransmission control module
What each part of P0812 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 8 | Area: transmission. |
| 12 | The exact fault in that area. |
What to do next
- Note P0812 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0812
What does P0812 mean?
P0812 means "Reverse Input Circuit". P0812 concerns the input 'reverse engaged' at the engine or transmission module – the reverse or back-up lamp switch on a manual gearbox, or the R contact of a selector. It is a generic code, so it means the same on every make.
Is it safe to drive with P0812?
P0812 does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will P0812 fail an emissions test?
P0812 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is P0812 to fix?
Difficulty: easy. A typical repair takes 0.5 to 1.5 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P0812 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.