Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
ECM Input Code EI74 - Park/Neutral Switch Circuit: Notes
The park/neutral switch is a part of transmission gear selector switch. Pin "A" of 6-pin connector on switch is park/neutral input for ECM and BCM. The park/neutral switch contacts are closed in park or neutral, shorting switch pin "A" to ground. In any other gear range, pin "A" is open.
The ECM sends 12 volts to pin "A" of gear selector switch over circuit No. 434. When gear selector is in park or neutral, the 12-volt signal from ECM is shorted to ground resulting in zero volts at ECM pin "A4". In reverse or forward gears, circuit No. 434 is open to ground resulting in 12 volts at ECM pin "A4".
A "HI" status on diagnostic display indicates that switch is open (not in park or neutral), a "LO" status indicates a closed switch (gear selector in park or neutral). The ECM uses park/neutral status for fuel and idle speed control, and as a test condition for many trouble codes.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.