P0812
Reverse Input Circuit
Transmission / range input
Generic OBD-II
Medium
What it means
P0812 means the transmission control module detected a problem with the reverse input circuit — the switch or sensor signal that tells it the vehicle has been placed in reverse. A fault here can prevent reverse from engaging properly or upset backup-lamp operation, but it does not stop the engine from starting or the vehicle from moving forward.
Medium
Can I keep driving? Usually drivable in forward gears, but reverse may not engage or may behave erratically — the engine still starts and runs. Get it fixed before you get stuck.
Common symptoms
What you'll notice
- Check-engine light on
- Reverse gear won't engage or is delayed
- Erratic or unexpected reverse engagement
- Reverse (backup) lights not working on some vehicles
Common causes
Most likely first
- Faulty reverse input switch or sensorLikely
- Damaged wiring or a poor connector in the reverse input circuitCommon
- Loose or corroded connectors in the transmission harnessCommon
- Fault elsewhere in the transmission range/switch circuitLess often
- Failed transmission control module (TCM)Less often
How to diagnose & fix
Work through it in order
- Scan for codes and read freeze-frame data to confirm the fault.
- Inspect the reverse input switch/sensor wiring and connectors for damage or corrosion.
- Test the reverse input signal as the shifter is moved into and out of reverse.
- Replace the reverse input switch or sensor if it doesn't signal correctly.
- If the switch and wiring are good, suspect the range circuit or TCM. Clear and re-test.
FAQ
Quick answers
Is it safe to drive with P0812?+
The engine starts and forward gears usually work, but reverse may be unreliable, so plan your parking. Get it repaired before it strands you.
Can I just clear P0812?+
It will clear, but returns once the module sees the bad reverse-input signal again unless the switch or wiring is repaired.
Related codes
Often seen with P0812
Read & clear P0812 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX