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 C-1A: Park/Neutral Switch Diagnosis (A/T)
The Park/Neutral switch contacts are part of neutral start switch. They 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 volt. The ECM uses this signal as one of the inputs to control IAC and VSS diagnostics.
- Checks for a closed switch to ground with transmission in Park position. Different makes of "Scan" testers will display P/N status differently. Refer to manufacturer's tester operation manual for type of display used.
- Checks for an open switch circuit in Drive.
- Be sure "Scan" indicates Drive, even while wiggling shifter to test for an intermittent or misadjusted switch in Drive.
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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.