OBD-II Generic Error Code P0851: How to Fix It

Q: What does error code P0851 mean?

P0851 means the PCM has detected a low voltage in the Park/Neutral Position switch circuit. This switch tells the PCM when the transmission is in park or neutral, and a low input can prevent the engine from starting.

Q: Can I drive my car with a P0851 code?

You may be able to drive, but the engine might not start if the switch is faulty. It's best to fix the issue promptly to avoid being stranded.

Q: How do I locate the Park/Neutral switch?

The PNP switch is usually located on the side of the automatic transmission, near the shift linkage. Some vehicles call it the neutral safety switch or transmission range switch.

Q: Will a bad Park/Neutral switch cause transmission problems?

While it mainly affects starting, a bad switch can also cause incorrect gear readings or prevent the reverse lights from working.

Q: Do I need to reset the PCM after replacing the switch?

Yes, after fixing the issue, clear the code with an OBD2 scanner or disconnect the battery for a few minutes. Drive the vehicle to see if the code returns.

Abstract

Error code P0851 indicates the Park/Neutral Position (PNP) switch circuit is reading a low voltage. This switch tells your engine computer whether the transmission is in park or neutral. A faulty switch or wiring issue can cause starting problems or prevent the engine from cranking.