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DTC codes / P08xx · Transmission / P0850

P0850Park/Neutral Switch Input Circuit

P0850 means the powertrain control module (PCM) has detected an unexpected voltage or signal on the park/neutral switch input circuit, so it cannot reliably tell whether the transmission is in park or neutral. The PCM compares the park/neutral signal with other inputs such as vehicle speed and gear position, and it sets this code when the circuit does not behave as expected.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaTransmission

Symptoms you may notice

  • The check engine light or service engine soon light is illuminated.
  • The engine may crank but not start because the PCM does not recognize park or neutral.
  • The starter may not engage when the shifter is in park or neutral.
  • The transmission may shift harshly or fail to enter certain gears.
  • Remote start or keyless ignition may not work because the vehicle does not confirm park.
  • Often no symptoms besides the warning light, especially if the fault is intermittent.

Common causes, most likely first

  1. A faulty park/neutral switch, also called a transmission range sensor or neutral safety switch.
  2. A damaged, corroded, or disconnected electrical connector at the switch.
  3. Broken, chafed, or shorted wiring in the park/neutral switch circuit.
  4. A poor ground connection for the switch or the PCM.
  5. A misadjusted or loose switch mounting that prevents correct alignment.
  6. A failed PCM or transmission control module (TCM) input circuit, though this is less common.

How to diagnose and fix it

  1. Scan all modules for stored and pending codes, and record freeze-frame data to see when P0850 set.
  2. Inspect the park/neutral switch connector and wiring for corrosion, damage, or loose pins.
  3. Check the switch adjustment and mounting, then verify the switch signal with a scan tool in each gear position.
  4. Test the switch electrically with a multimeter for continuity or voltage changes as the shifter moves.
  5. Check ground circuits and power supply to the switch and PCM using a wiring diagram.
  6. Repair or replace damaged wiring, connectors, or the switch as needed, then clear codes and retest.
  7. Perform a road test and verify the code does not return, and confirm the starter works in park and neutral.

Park/Neutral Switch Circuit Checks That Save Time

  • A park/neutral switch fault can prevent the engine from cranking because the PCM uses this signal to enable the starter, so always check the switch before condemning the starter.
  • Aftermarket remote start systems and alarms often tap into the park/neutral wire, and a poor splice there can set P0850 even when the factory switch is fine.
  • On some vehicles the park/neutral signal is derived from the transmission range sensor or an internal mode switch, so a transmission range sensor code may also be present and should not be ignored.
  • A misadjusted switch can set P0850 intermittently when the shifter is moved, and the code may not return until the vehicle is driven through several gear changes.
  • Do not replace the PCM based on P0850 alone; verify the switch signal at the PCM connector with a scan tool or meter before assuming the module is faulty.

Can I keep driving with P0850?

You can usually drive the vehicle if it starts and moves, but avoid situations where you must rely on park or neutral recognition, such as remote start or leaving the car unattended while running. If the engine will not crank in park or neutral, do not keep trying; have the circuit diagnosed, because a no-crank condition can leave you stranded.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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