P0855 Code: Drive Switch Input Circuit High

What the P0855 code means

Some transmissions have a switch that confirms the shift lever is in D. The computer compares its signal with the transmission range sensor.

It is a simple switch, so the computer sees either a high or a low voltage depending on its position. The P0855 code is set when that signal sits above its maximum. A high signal usually comes from an open circuit or from an interrupted ground.

When the signal fails, the transmission can go into limp mode or refuse certain gears. The transmission range sensor is tested the same way, so check it as well.

To confirm the diagnosis, measure the continuity of each wire between the component connector and the computer connector with the key off. It should be under 1 ohm, and an infinite reading means the wire is open. If the wiring is good, measure the component itself: an infinite resistance confirms it is open inside.

P0855 code symptoms

• Check engine light on.
• Transmission in limp mode.

Likely causes of the P0855 code

1. Loose or broken connector. This is the most frequent cause.
2. Signal wire or ground wire cut, so the signal climbs up to the reference voltage.
3. Switch open inside, with infinite resistance.
4. Short to 5 V or 12 V from rubbing against another wire in the harness.

How to diagnose the P0855 code step by step

1. Read the switch value on the scan tool and compare it with what you expect.
2. Inspect the connector for corrosion, water or loose pins.
3. Check power and ground with the key on: the reference should be correct and the ground voltage drop should be under 0.1 V.
4. Measure the signal with the connector plugged in and see whether it changes with the lever position.
5. Do a wiggle test on the harness with the scan tool in graph mode.
6. Check continuity of each wire to the computer (under 1 ohm).

How to fix the P0855 code

• Repair the connector or the wiring.
• Replace the switch if the tests confirm it is bad.
• Correct the real condition if there is one.
• Clear the codes and verify with a road test.

Technical reference data

• The switch or sensor is powered from the computer. Check the values in the service manual.
• Reference values are only a guide, so look up the manufacturer data for your vehicle.
• Wire continuity should be under 1 ohm, and ground voltage drop under 0.1 V.

Brand-specific notes

The letter assignment and the location of the component change from one manufacturer to another, so check the manual for your vehicle before you start testing.

A P0855 code is easier to read when you compare the Drive switch with the range sensor on the scan tool. If the two disagree about the lever position, you have found the side that is lying.

Frequently asked questions about P0855