P0851: Park/Neutral Switch Input Circuit Low
What to do
The car will start normally, which is exactly why this matters — the safeguard against cranking with a gear engaged may no longer be working. Always confirm neutral and apply the parking brake before starting until it is repaired.
What this code means
The park/neutral signal reads below its valid range, normally a short to ground, which the module takes as park or neutral being permanently selected. The consequence is the unsafe direction of this fault: the starter interlock believes it is always safe to crank, so the protection against starting in gear is gone even though the engine starts perfectly.
Likely causes
Start here
- Wiring shorted to ground · moderate
- Faulty park neutral switch · moderate
Less common
- Corroded or loose connector · easy
- Misadjusted transmission range sensor · moderate
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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