FixItFor.Us
P codepowertrainMedium severity

P086ANeutral Position Sensor "A" Circuit/Open

The transmission neutral position sensor "A" circuit has an open or general fault, so the control module cannot reliably tell when the transmission is in neutral.

Definition

On automated manual and dual-clutch transmissions (and some manuals equipped for stop/start), a neutral position sensor tells the TCM/PCM when the gearbox is actually in neutral, which gates starter engagement, stop/start operation, and shift actuator control. P086A sets when the module detects an open circuit or an implausible general electrical fault on the sensor "A" circuit, such as no signal voltage present at all. Symptoms include a crank/no-start or refusal to auto-start, stop/start being disabled, hesitant or blocked gear engagement, and a transmission warning light; the MIL may also illuminate depending on calibration.

Common causes

  • Neutral position sensor failed open internally
  • Broken wire or open in the sensor harness
  • Disconnected, corroded, or backed-out terminal at the sensor or TCM connector
  • Loss of 5V reference supply to the sensor
  • Sensor knocked loose or mispositioned after clutch/transmission service
  • Faulty TCM input circuit (rare)

Common misdiagnoses

  • Replacing the starter for the resulting no-crank condition
  • Replacing the shift actuator assembly instead of the sensor
  • Replacing the park/neutral safety switch on vehicles that use a separate sensor
  • Replacing the battery for stop/start inhibits

Troubleshooting steps

  1. 1.Read the sensor state on a scan tool

    Compare the reported neutral status against the actual gear position while moving the selector; a status that never changes or reads invalid confirms a circuit problem.

  2. 2.Inspect the sensor connector and harness

    Locate the neutral position sensor on the transmission case or shift mechanism and check for unplugged connectors, corrosion, and chafed wiring near moving linkage.

  3. 3.Verify supply voltage and ground

    Key on, confirm the sensor receives its 5V reference (or switched battery voltage on some designs) and that the ground circuit drops less than 0.1V.

  4. 4.Check circuit continuity to the TCM

    With both ends disconnected, measure end-to-end resistance on the signal wire; more than about 1 ohm or an open reading means a harness break, often at flex points or connector crimps.

  5. 5.Test or substitute the sensor

    Back-probe the signal wire while shifting between neutral and in-gear; the voltage should switch or sweep per spec, and a dead output with good supply confirms a failed sensor.

Related codes