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.
DTC P1634: Improper Ignition 1 Input: Description
The Powertrain Control Module (PCM) receives three ignition inputs from the ignition switch: ignition 0 signal, ignition 1 signal, and crank signal. The PCM receives the ignition 1 signal with the ignition switch in the ON and START positions. The PCM uses a Class II ignition mode message and voltage input from the ignition switch to test the ignition 1 voltage circuit. If the PCM detects an improper ignition 1 signal, DTC P1634 will set.
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.