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 P0718: Input Shaft (Mainshaft) Speed Sensor Intermittent Failure: General Description
The mainshaft speed sensor is attached to the outside of the transmission housing. The mainshaft speed sensor generates a pulsing signal according to the speed of the mainshaft idler gear on the mainshaft. Using that signal, the powertrain control module (PCM) determines the speed of the mainshaft. If no pulses occur with the mainshaft rotating, the PCM detects a malfunction that may be caused by an open, a temporary open, or a short to ground. Based on the fluctuation of the vehicle speed measured by the mainshaft speed sensor, a malfunction is detected and a DTC is stored.
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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.