Faulty drive switch or selector position switch, or one that is out of adjustment; Wiring fault such as a signal wire short to voltage, or chafed or damaged loom; Corroded, loose or water-damaged connector at the switch or control unit; Open circuit in the switch ground or return, which pulls the input high; Worn or misaligned gear selector linkage or cable giving a wrong switch position; Fault inside the transmission or powertrain control unit.

P0855

Drive Switch Input Circuit High.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
8: AreaTransmission
55: FaultThe specific fault in that area

What it means

P0855 means the control unit has seen a voltage that is too high on the drive switch input circuit. The drive switch signal tells the powertrain or transmission control unit which drive mode or selector position has been chosen. The code sets when the signal sits above the expected range, or does not match other inputs such as the park/neutral or range sensor. What the drive switch is, and where it is fitted, varies by make and model.

Symptoms

Warning light on, possibly with a transmission or gearbox warning
Gearbox stuck in a default gear or in limp mode
Harsh, delayed or missing gear engagement
Drive mode or selector position not recognised or shown wrongly on the dash
Engine will not start, or starts only in certain selector positions
Other related transmission range or neutral switch codes stored

Possible causes

Faulty drive switch or selector position switch, or one that is out of adjustmentlikely
Wiring fault such as a signal wire short to voltage, or chafed or damaged loomlikely
Corroded, loose or water-damaged connector at the switch or control unitlikely
Open circuit in the switch ground or return, which pulls the input highpossible
Worn or misaligned gear selector linkage or cable giving a wrong switch positionpossible
Fault inside the transmission or powertrain control unitrare

How to diagnose

Read all stored and pending codes and note the freeze frame data, looking for related range, neutral or transmission codes
Check for any software or service information that applies to the model, as the switch type and location vary
Inspect the switch, connectors and wiring for damage, corrosion, water ingress, chafing and loose pins
Check the selector linkage or cable is secure, correctly adjusted and moves through all positions
With a scan tool, watch the live drive switch or selector position data while moving through each position and see whether it follows or stays stuck high
Measure the reference voltage, signal and ground at the switch connector against the manufacturer's specification
Check the signal wire for a short to voltage and the ground for an open circuit, with the connectors unplugged
Clear the code and road test to see whether it returns before condemning the control unit

How to fix

Repair or replace the damaged wiring, and clean or replace corroded connectors
Replace the drive switch or selector position switch if it is faulty
Adjust or repair the selector linkage or cable, then set the switch to specification
Restore the switch ground or reference circuit if it is open
Replace or reprogram the control unit only if testing proves it faulty, or if the manufacturer lists a calibration update for this fault

Can I keep driving?

Medium severity

The car can usually be driven carefully for a short time, but the gearbox may be in limp mode or behave unpredictably. Get it checked soon, and avoid driving if it will not select gears reliably or starts in an unsafe condition.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.