B1751
Park/Neutral Switch Circuit Short To Battery
Body Transmission Control Park/Neutral Switch 🟢 Low — Fix at next service
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What This Actually Means
In plain language — no jargon

The park/neutral switch is sending a constant 'battery voltage' signal to the ECU instead of switching between two states, like a light switch stuck in the 'on' position. This tells the ECU the transmission is always in park or neutral even when it's not.

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Symptoms You May Notice
3 known symptoms for this code
Check Engine Light illuminated
Transmission may not shift or engage properly
Engine may not crank or starts unexpectedly
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Embedded Systems Insight
What the ECU/ECM is actually computing

The ECU monitors the park/neutral switch voltage signal, which should toggle between ground and battery voltage depending on transmission gear selection. When the circuit shorts to battery voltage, the signal remains continuously high, preventing the ECU from detecting actual gear position changes.

Voltage & Parameter Thresholds

Parameter Normal Range Fault Condition
Park/Neutral Switch Voltage 0V (Park/Neutral) or 5V (Drive/Reverse) Continuous 12V battery voltage
Signal State Detection Switches between states with gear selection Remains in one fixed state regardless of gear
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Diagnostic & DIY Fix Guide
Check these in order — from cheapest to most complex
1
Wiring harness connector
Inspect the park/neutral switch connector for corrosion, loose pins, or damaged insulation and reseat or clean as needed.
2
Park/Neutral switch
Replace the switch if inspection reveals internal failure or a stuck contact creating the short to battery.
3
Engine wiring harness
Repair or replace any damaged wiring between the switch and ECU that may be shorted to the battery positive line.