P0855: Drive Switch Input Circuit High

What it means

The drive (D) switch input reports a input circuit high fault. Drive mode selection cannot be reliably detected.

At a glance

• Usually lights the check-engine light

How it works

The drive switch signals when the selector is in Drive. This code sets when the control module detects an input voltage above its expected range, such as from a signal wire shorted to battery voltage or a switch that stays open.

Common causes

Most likely first.

1. Wire shorted to B+
2. Switch stuck open
3. Connector pins corroded - high contact resistance

Symptoms

• Check engine or transmission warning light on
• Harsh, delayed, or missing shifts
• Possible limp mode (locked in one gear)
• Slipping or shuddering during gear changes

How to diagnose it

1. Record freeze-frame data and watch live selector-position data while moving the lever into and out of Drive.
2. Inspect the drive switch wiring for damage or contact with a power feed, and check connector pins for corrosion or poor contact.
3. Using the manufacturer's circuit test procedure, check whether the input wire is shorted to battery voltage.
4. Test the drive switch for the expected open and closed states across selector positions.
5. If circuit and switch checks pass, inspect the module connector and review related transmission codes before suspecting a module fault.

Common fixes

• Clean and reseat the drive switch connector.
• Repair a signal wire shorted to battery voltage or damaged harness insulation.
• Replace a drive switch stuck open.
• Repair a faulty module connection if the switch and wiring test correctly.

Can I keep driving?

If the vehicle cannot reliably recognize Drive or develops harsh, delayed, or slipping shifts, stop driving and arrange diagnosis. Continuing with uncertain gear selection can make the vehicle unpredictable in traffic.