P0855
Drive Switch Input Circuit High
Powertrain Transmission Control Drive Switch Input 🟡 Moderate — Fix within a week
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What This Actually Means
In plain language — no jargon

The ECU detected that a drive switch input signal is stuck in a high voltage state when it should be low or cycling normally. Think of it like a light switch that's jammed in the 'on' position—the ECU can't tell if the driver is actually pressing it.

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Symptoms You May Notice
3 known symptoms for this code
Check Engine Light illuminated
Transmission may not shift properly or stay in limp mode
Engine may run rough or idle erratically
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Embedded Systems Insight
What the ECU/ECM is actually computing

The ECU monitors the drive switch input circuit voltage to detect when the driver engages transmission controls or cruise functions. The circuit should toggle between high and low states or remain at a specific voltage. A persistently high signal indicates a wiring fault, stuck switch, or pulled connector.

Voltage & Parameter Thresholds

Parameter Normal Range Fault Condition
Drive Switch Input Voltage 0V–2V (low) or 4.5V–5V (high) with normal switching Stuck above 4.5V when low signal expected
Signal Response Time Responds within 100ms of input No voltage change or extremely delayed response
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Diagnostic & DIY Fix Guide
Check these in order — from cheapest to most complex
1
Drive switch connector
Locate and reseat the connector fully; corrosion or loose pins often cause high voltage faults.
2
Wiring harness and connectors
Inspect for damaged insulation, crushed wires, or exposed conductors bridging to 12V power.
3
Drive switch assembly
Replace the switch if it is stuck internally or contacts are welded shut.