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.
Code 24 - VSS Circuit: Notes
The ECM applies and monitors 12 volts on circuit No. D8. The Vehicle Speed Sensor (VSS) alternately grounds and opens circuit from ECM terminal No. D8 when vehicle is in motion. This pulsing action takes place about 4096 times per mile. ECM will calculate vehicle speed based on time between pulses. With vehicle in motion, Scan tester reading should closely match speedometer reading.
- Code 24 will set if vehicle speed equals zero MPH when engine speed is between 1600 and 1825 RPM, MAP reading below 3.0 psi (20.7 kPa), low speed condition (low MAP voltage, high manifold vacuum), vehicle not in Park or Neutral (A/T), all conditions met for 1.5 seconds and Code 33 is not set. These conditions are met during a load deceleration. Disregard Code 24 which sets when vehicle is not in motion.
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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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