What Does P0812 Mean?
The Reverse Input Circuit has detected a fault. This circuit receives the signal indicating the transmission has been shifted into reverse gear. The PCM uses this input to activate reverse lights, adjust idle speed, disable cruise control, and provide reverse camera activation on some vehicles. The signal is not being received as expected.
Common Causes
35%
Faulty reverse light switch / reverse gear position switch
25%
Open or shorted wiring in the reverse input circuit
20%
Misadjusted transmission range sensor or gear position sensor
12%
Corroded connector at the reverse switch on the transmission
8%
PCM input circuit fault
Diagnostic Steps
1
Shift into reverse and check if the reverse lights illuminate — if they do not, the switch or circuit is likely faulty.
2
Monitor the reverse input PID on the scan tool while shifting between neutral, reverse, and drive to verify signal transitions.
3
Locate the reverse light switch on the transmission and test it with a multimeter — it should close (show continuity) when the transmission is in reverse.
4
Inspect the wiring from the reverse switch to the PCM for damage, especially where it runs along the transmission and underbody.
5
If the vehicle uses a transmission range sensor instead of a discrete switch, check its adjustment and signal per manufacturer specs.
Estimated Repair Cost
$30 - $300
Parts + labor, varies by vehicle and location
The Reverse Input Circuit has detected a fault. This circuit receives the signal indicating the transmission has been shifted into reverse gear. The PCM uses this input to activate reverse lights, adjust idle speed, disable cruise control, and provide reverse camera activation on some vehicles. The ...
The most common cause of P0812 (Reverse Input Circuit) is: Faulty reverse light switch / reverse gear position switch
Typical repair costs for P0812 range from $30 to $300, depending on the vehicle, location, and whether you do it yourself or go to a shop.
The vehicle can be driven, but reverse lights may not function, making reversing dangerous especially at night. Other systems dependent on the reverse signal (backup camera, parking sensors) may also be inoperative. Repair promptly for safety.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0812 to identify the root cause.
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Quick Info
Category
Powertrain
System
Transmission Control / Lighting System
Difficulty
Type
Generic (SAE)
Recommended Tools
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