Error Code P0850 is defined as Park/Neutral Switch Input Circuit. Error Code P0850 is a generic trouble code, meaning it applies to all vehicles with the OBD-II system, especially those made from 1996 up to present. It also applies to vehicles with both automatic transmission and 4WD capability. Specifications on the definition, troubleshooting, and repairs, of course, vary between make, model, and powertrain configuration.

If the PCM stores this code, this means the input circuit that measures the function of the park/neutral switch shows abnormal voltage reading.

If a vehicle is put into a park or neutral, a voltage reading from various components and sensors will be sent to the PCM. This ensures the PCM that the park and neutral are achieved, and it is working properly. If the voltage reading that comes from the input circuit on the park/neutral switch doesn’t match the specifications set by the manufacturer, then 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

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 park/neutral switch
  • Faulty electrical connection in park/neutral switch circuit
  • Open or shorted park/neutral switch harness
  • Faulty range sensor
  • Faulty wiring or electrical components
  • Faulty installation of sensor retaining bolts
  • Excessive corrosion in the sensor connector

How to Check

First, use the OBD-II scanner to verify the error code. After this, you can proceed with the visual inspection of the electrical components, connectors, and wirings. Repair or replace as necessary, then clear the code, reset the system, and see if it comes back.

If the code comes back, check the battery voltage and ground signals at the park/neutral switch.

Make sure you compare the readings with the specifications set by the manufacturer. If the readings are within the acceptable range, then the sensor is in good shape. However, if the readings are outside the acceptable range, then try other repairs. Ensure you clear the codes and reset the system after each potential repair process to make sure the correct repairs are being done.

How to Fix

  • Repair damaged or faulty electrical components, connectors, and wirings in the park/neutral switch circuit
  • Replace defective park/neutral switch
  • Adjust transfer case range sensor
  • Replacement of defective range sensor
  • Replacement of faulty wiring or electrical components
  • Proper installation of sensor retaining bolts
  • Replacement of corroded sensor connector

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

Since this code related to the drivability of the vehicle, the fault is considered urgent. Allowing the problem to sit can cause serious damage and result in unsafe conditions for the vehicle, 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.