P0851 Fault Code

Park / Neutral Switch Input Circuit Low

• What does that mean?
• Symptoms
• Causes
• Solutions

The P0851 fault code indicates a low voltage or an improper signal coming from the Park/Neutral switch input circuit. This switch is responsible for ensuring that the transmission is in park or neutral before the engine can start. When this circuit malfunctions, it can prevent the vehicle from starting or cause other transmission-related issues.

What are the symptoms of the P0851 code?

• The engine will not start
• The vehicle may unexpectedly start in drive
• Transmission may not shift properly
• Check engine light is illuminated
• Difficulty in shifting gears or finding the correct gear

What causes the P0851 code?

• Faulty Park/Neutral switch
• Damaged wiring or connectors in the circuit
• Short circuits or open circuits in the wiring
• Issues with the engine control module (ECM)
• Corrosion in electrical connections

How to fix P0851?

• Inspect and test the Park/Neutral switch for proper function
• Repair or replace damaged wiring and connectors
• Check for shorts or opens in the circuit
• Clean any corrosion found in electrical connections
• If all else fails, consider testing or replacing the ECM