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.
Circuit Description
Crankshaft position sensor and camshaft position sensor are used to detect misfire. VCM monitors crankshaft speed and detects deceleration or acceleration of crankshaft that are not associated with normal engine speed. Crankshaft position sensor information is compared to engine speed and engine load to determine if a misfire occurred.
If a misfire is present, crankshaft position is compared to camshaft position sensor signal to determine which cylinder misfired. Information will be stored in separate accumulators for each cylinder. VCM evaluates number of misfires in each accumulator. A random misfire is determined if accumulators are somewhat the same, or if 3 or more cylinders are misfiring.
VCM also utilizes input from front wheel speed sensor to determine if a rough road condition exists which could cause crankshaft acceleration and deceleration. Diagnostic will not run if a rough road condition exists.
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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.
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