Transmission

P0850 — Park/Neutral Switch Input Circuit Fault

Severity: medium Drive with care, to a shop

What P0850 means

The engine or transmission control module monitors the park/neutral switch, which reports whether the shifter is in Park or Neutral. That signal allows the starter to engage and also helps manage idle and shift control. P0850 sets when the signal is missing, illogical, or disagrees with the selector position and other data.

Symptoms

  • Engine will not crank
  • Engine starts in gear, not just Park or Neutral
  • Check engine light on
  • Unstable idle when moving the shifter
  • Wrong gear position shown on the dash
  • Harsh or odd automatic shifting

Possible causes

  1. Failed or worn park/neutral (neutral safety) switch
  2. Misadjusted shifter linkage or cable
  3. Open, shorted, or corroded wiring or connector at the switch
  4. Moisture or fluid in the switch connector
  5. Loose switch mounting
  6. Rarely, a faulty engine or transmission control module

How to diagnose

  1. Read all codes and freeze-frame data, and note any other transmission codes
  2. With a scan tool, watch the displayed gear position as you move the shifter through P, R, N, D
  3. Confirm the shifter position matches the actual position at the transmission
  4. Inspect the shift cable or linkage for play, wear, and correct adjustment
  5. Inspect the switch connector and harness for corrosion, moisture, and damage
  6. Use a multimeter to check power, ground, and switch resistance per the vehicle's wiring diagram
  7. Verify the engine only starts in Park and Neutral, and adjust the switch
  8. If the switch and wiring are good, test the control module

Common fixes

  • Adjust the park/neutral switch
  • Adjust or replace the shift linkage or cable
  • Repair the wiring and clean or replace the connector
  • Replace the park/neutral switch
  • Reflash or replace the control module only after confirming it is faulty

Questions and answers

What does P0850 mean?

The control module sees an invalid signal from the park/neutral switch. The usual culprits are the switch itself, shifter adjustment, or wiring.

Can I drive with P0850?

Often yes, while the car starts and drives normally, but repair it soon. The risk is that the engine may not start, or may start while in gear.

How do I clear P0850?

Fix the cause first by adjusting or replacing the switch or repairing the wiring. Then clear the code with a scan tool and confirm it does not return.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.