Reverse Input Circuit


The PCM has detected a fault in the reverse input circuit. When the shifter is placed in reverse a switch is energized. Voltage from this switch is monitored by the PCM. This switch is often used to activate “back-up lamp” operation, as well.

Code Set Parameters

If the PCM detects an abnormal voltage or resistance reading from the reverse input circuit, a code will be stored and a malfunction indicator lamp may be illuminated. Some vehicles will require multiple failure cycle in order for a service engine soon lamp to be illuminated and some models will not illuminate a service engine soon lamp at all.


Symptoms may include failure of the back-up lamps to illuminate, a stored code, and possibly an illuminated service engine soon lamp.

Common Causes

The most common causes of this type of malfunction code being stored are due to a defective reverse input switch. Other possible causes include shorted, open, or corroded wiring and/or electrical connectors.

Common Misdiagnosis

Technicians report that the back-up lamp bulbs are frequently condemned in error when the reverse input switch, wiring, or connectors are at fault.


  • A scanner (or code reader) and a digital volt/ohmmeter will be helpful in successfully diagnosing the potential causes of this code. This code is used in vehicles with automatic transmission and vehicles with manual transmission, too
  • In vehicles which are equipped with an automatic transmission, this switch may be part of a neutral safety switch or a manual lever position sensor
  • In vehicles with a manual transmission, the switch is typically threaded into the transmission housing near the shifter. While the reverse input switch may vary by design from one manufacturer to another, it is usually of the “on/off” contact variety
  • Regardless of design, constant voltage is typically present on one side of the switch and when the contacts in the switch are closed, voltage is transferred across the contacts and out of the switch to the back-up lamps and the PCM. Begin your diagnosis with a visual inspection of all wiring and connectors
  • Repair or replace damaged, disconnected, shorted, or corroded wiring, connectors, and components as necessary
  • Always retest the system after repairs are completed to ensure success. If all system wiring, connectors, and components (Including fuses) appear to be in normal working order, connect the scanner (or code reader) to the diagnostic connector and record all stored codes and freeze frame data
  • This information can be extremely helpful in diagnosing intermittent conditions that may have contributed to this code being stored
  • After the codes are cleared, operate the vehicle to see if the code returns
  • If the code fails to immediately return, you may have an intermittent condition
  • Intermittent conditions can prove to be quite a challenge to diagnose and in extreme cases may have to be allowed to worsen before a correct diagnosis can be made
  • If the code immediately returns, check for battery voltage on the input side of the reverse input switch using the digital volt/ohmmeter
  • If there is no voltage present on the input side of the switch, disconnect any related control modules and check for continuity between the system fuse and the input circuit at the reverse input switch
  • Repair open or shorted circuits as required
  • If voltage is present on the input side of the reverse input switch, secure the vehicle and place the shifter in reverse
  • Check for voltage on the output side of the reverse input switch
  • If you have voltage on the input side and none on the output side (with the shifter in reverse) suspect a faulty or misadjusted reverse input switch
  • Adjust or replace the switch as needed and retest the system afterward to ensure a successful repair. If there is voltage present on the output circuit of the clutch input switch, check circuit continuity and resistance between the switch and the PCM
  • Again, refer to the vehicle wiring diagram to ensure that all circuits are tested
  • Repair or replace system open or shorted circuits/connectors as required
  • If all circuits coincide with manufacturer’s specifications, suspect a defective PCM
  • Remember that PCM failure is rare and replacement will require reprogramming