Error Code P0855 is defined as Drive Switch Input Circuit High. Error Code P0855 is a generic trouble code, meaning it applies to all vehicles with the OBD-II system, especially those made from 1996 up to the present. It also applies to vehicles with both automatic transmission and 4WD capability. Specifications on the definition, troubleshooting, and repairs vary between make, model, and powertrain configuration.

This error code is related to the transmission, including pressure faults and sensor failures. If this code is stored, that means the Powertrain Control Module (PCM) has determined a fault or malfunction in the switch input circuit. The drive switch works by telling the ECM which transfer case is in. Most drive switches are of variable resistance. This switch is found over the transfer case shift shaft. The shift lever will slide over it. Moving the shift lever will pivot the sensor to hit different contacts. Each contact will send the ECM voltage levels and help it determine the shift strategy, among others.

The vehicle’s transfer case shift select range sensor sends data to the PCM. The latter then uses this data to calculate the engine timing, RPM, fuel delivery, etc. if the data the PCM receives is higher than the expected transmission shifter range, this code will be stored.

Common Symptoms

As with other error codes, the Check Engine Light is activated with this code. Other common symptoms include:

  • Harsh shifting or failure to shift
  • Unable to engage 4WD
  • Increased fuel consumption
  • Vehicle may enter “limp mode”

Possible Causes

A misadjusted transfer case range sensor usually causes this error code. This could have resulted from improper installation from the previous repair. Other possible causes include:

  • Defective range sensor
  • Improperly installed sensor retaining bolts
  • Corroded sensor circuits
  • Open, shorted, corroded, or damaged electrical components such as connectors and wirings

How to Check

First, use the OBD-II scanner to check the stored error code.

Next, inspect the connectors and system wirings. Look for signs of damage and corrosion.

Check the drive switch for ground signals and battery voltage.

If the battery voltage or ground signals are open, check the circuits for continuity and resistance using the digital volt/ohmmeter.

Lastly, test all the related circuitry and the sensor for continuity and resistance. Compare it with the specifications set by the manufacturer.

How to Fix

  • Repair or replacement of damaged system wiring and connector
  • Replacement of defective or damaged drive switch
  • Retest the system, repair any damages or defects in the wiring
  • Replacement of damaged transfer case range sensor

The most common mistake in diagnosis this code is assuming the transfer case range sensor is faulty when it is simply misadjusted.

Since this code related to the drivability of the vehicle, the fault is considered urgent. Allowing the problem to sit can cause severe damage and result in unsafe driving conditions, which can lead to more expensive repairs.

If this code is detected, it is best to take your vehicle to a qualified technician. They have the expertise and advanced tools for a thorough diagnosis and proper repair.