Fault codeP0851

MODERATE

Park / Neutral Switch Input Circuit Low

What this code means

Park / Neutral Switch Input Circuit Low.

P0851 is a generic code: it means the same thing on every make. P0851 belongs to family P08xx — Transmission (continued). Its page explains how to read a code and groups all its codes by part.

Type of fault

The control unit reads a voltage on this circuit below its expected range. Usual causes: a wire shorted to ground or broken, a corroded or loose connector, or the component itself. Check the wiring and connector before replacing the part — that is where many of these faults turn out to be.

Gear selector position switches

These switches tell the control units whether the selector is in Park, Neutral, Drive or Reverse. They only allow starting in Park or Neutral, light the reversing lights and lock out reverse while moving on some gearboxes.

What you notice

The engine will not start in Park, reversing lights that do not work, shift indicator wrong on the dashboard.

How to check it

Check the switch on the gearbox, its adjustment with the selector cable and its connector, which is exposed to dirt and water. A slightly misadjusted selector cable is a frequent cause.

Watch it live in Klaro

With an OBD2 adapter plugged in, these live readings show the part at work, when your car reports them:

Vehicle speed

What to do

Have it checked this week. The car remains usable, but the fault will not clear itself and will fail the roadworthiness test.

Clearing a code switches the light off but repairs nothing: if the fault remains, the code comes back. Clearing a fault code yourself →

How to read this code

PPowertrain
0standardised code
8Transmission (continued)
51P0851