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DTC codes / P08xx · Transmission / P0855

P0855Drive Switch Input Circuit High

P0855 is a generic powertrain code indicating that the powertrain control module (PCM) has detected a high voltage condition on the drive switch input circuit, which is typically associated with the transmission range sensor or park/neutral switch. The PCM expects a specific voltage on this circuit when the gear selector is in a given position, and a reading above the normal threshold triggers this code.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaTransmission

Symptoms you may notice

  • The check engine light or service engine soon light is illuminated.
  • The engine may crank but fail to start because the PCM does not recognize the park or neutral position.
  • The transmission may not shift properly or may stay in a single gear (limp mode).
  • The reverse lights may not illuminate when reverse is selected.
  • The gear position indicator on the dashboard may be inaccurate or blank.
  • Often no symptoms besides the warning light, especially if the fault is intermittent.

Common causes, most likely first

  1. A faulty transmission range sensor (also known as park/neutral safety switch) that is internally shorted to voltage.
  2. Damaged or corroded wiring in the drive switch input circuit, such as a chafed wire shorting to a power source.
  3. A poor electrical connection at the sensor or PCM connector, causing a high resistance or intermittent open.
  4. A failed PCM driver or internal fault in the PCM, though this is less common.
  5. Water intrusion into the sensor or connector, leading to corrosion and voltage irregularities.
  6. Aftermarket accessories or improper wiring repairs that backfeed voltage into the circuit.

How to diagnose and fix it

  1. Use an OBD-II scanner to retrieve all codes and verify that P0855 is current; clear the code and test-drive to see if it returns.
  2. Visually inspect the transmission range sensor and its connector for corrosion, damage, or loose pins; repair or replace as needed.
  3. Check the wiring harness between the sensor and PCM for shorts to voltage or chafed insulation; repair any damaged wires.
  4. Measure the voltage on the drive switch input circuit at the PCM connector with the key on and engine off; compare to the manufacturer's specification.
  5. Test the transmission range sensor with a multimeter for proper continuity and resistance in each gear position; replace if out of spec.
  6. If all external circuits and components test good, suspect an internal PCM fault; consult a professional before replacing the PCM.
  7. After repairs, clear the codes and perform a relearn or calibration procedure if required by the vehicle manufacturer.

Don't overlook the range sensor connector

  • A common misdiagnosis is replacing the PCM when the actual problem is a corroded connector at the transmission range sensor, which can mimic a high voltage fault.
  • The drive switch input circuit is often shared with the reverse light circuit on some vehicles, so a short in the reverse light wiring can set P0855.
  • Intermittent high voltage readings can be caused by a loose ground connection at the transmission, leading to a floating voltage on the signal circuit.
  • Some vehicles use a linear range sensor rather than a simple switch, and a faulty sensor can produce a high voltage signal without any drivability symptoms.
  • Aftermarket remote start systems or alarm installations that tap into the park/neutral circuit are a frequent cause of unexplained P0855 codes.

Can I keep driving with P0855?

If the vehicle starts and drives normally, you can drive it to a repair shop, but avoid relying on the reverse lights or gear indicator. If the engine will not start or the transmission is in limp mode, do not drive; have the vehicle towed to avoid further damage.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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