P086C

What it means

P086C is the generic code for a low voltage or signal fault in the neutral position sensor 'A' circuit. The control unit saw a signal voltage below the expected range, which points to a short to earth, an open circuit or a faulty sensor. Where the sensor is fitted and what it is used for (engine start permission, stop-start, gear position logic) depends on the vehicle and gearbox type.

Symptoms

• Engine fails to start or only starts with the clutch pedal pressed or the selector moved
• Stop-start system not working
• Gear indicator missing, wrong or flickering on the dash
• Harsh, delayed or unexpected gearbox shifts on automated or automatic gearboxes
• Engine management warning light on
• Reversing lights or cruise control behaving oddly on some models

Possible causes

• Neutral position sensor or switch faulty internally (short to earth or open circuit)likely
• Damaged, chafed or corroded wiring to the sensor, giving a short to earth or open circuit on the signal linelikely
• Poor connector contact or water ingress at the sensor or gearbox pluglikely
• Sensor misadjusted, loose or damaged mechanically, or linkage worn, so it reads out of rangepossible
• Low or missing sensor supply voltage or poor earth from a wiring or fuse faultpossible
• Faulty control unit (engine or transmission) or outdated software, where the manufacturer has identified onerare

How to diagnose

1. Read all stored and pending codes and the freeze frame data, noting gear, speed and whether the fault is current or intermittent
2. Check for related codes such as supply voltage, gear position or communication faults, which can point to a shared wiring or power problem
3. Visually inspect the sensor, its wiring and connector for damage, corrosion, oil or water contamination, and rubbing points
4. Wiggle test the harness and connector with live data showing the neutral signal to see whether it drops out
5. Check the live neutral signal while moving the selector or shift through all positions and compare with the manufacturer's specification
6. Check sensor supply, signal and earth with a multimeter against the wiring diagram, and test the wiring for short to earth and continuity
7. Check the sensor mounting and linkage adjustment where the design allows it
8. Check for relevant technical service bulletins and software updates for the model and gearbox

How to fix

• Repair or replace damaged wiring and fix any short to earth or open circuit found
• Clean, repair or replace the corroded or loose connector terminals and seal out moisture
• Replace the neutral position sensor or switch if it fails testing, and adjust or set it up as the manufacturer requires
• Correct the mounting or linkage adjustment, or replace worn parts
• Restore the supply or earth fault found in the circuit
• Update the control unit software only if a known fault requires it, or replace the unit if it is proven faulty

Can I keep driving?

Nearby codes

• P086BGenericNeutral Position Sensor A Range/Performance
• P086DGenericNeutral Position Sensor A Circuit High