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.
Chart C1A - Park/Neutral Switch A/T (A/F/J/N/P Body)
The park/neutral switch contacts are part of neutral start switch, are closed to ground in park or neutral, and open in drive ranges. The ECM supplies ignition voltage through a current limiting resistor to circuit No. 434, and senses a closed switch when voltage on circuit No. 434 drops to less than one (1) volt. The ECM uses this signal as one of the inputs to control IAC and VSS diagnostics.
- Checks for closed switch to ground in park position. Use an ohmmeter instead of a test light to 12 volts. Resistance will be low indicating continuity to ground.
- Checks for an open switch in drive range. Use an ohmmeter instead of a test light to 12 volts. Resistance will be high or infinity, indicating an open switch.
- Checks to this point indicate park/neutral switch and wiring are okay. The ECM signal voltage on circuit No. 434 may be missing. To check, reconnect ECM. Either back probe ECM connector circuit No. 434 with selector in drive or disconnect park/neutral switch. Probe harness connector circuit No. 434 with a voltmeter to ground.
NO RELATED
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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.