Code 24: VSS Circuit: Notes

The ECM applies and monitors 12 volts on circuit Yellow No. 03. Vehicle Speed Sensor (VSS) alternately grounds and opens circuit Yellow No. 03 when vehicle is in motion. This pulsing action takes place about 2000 times per mile. ECM will calculate vehicle speed based on the time between "pulses". With vehicle in motion, "Scan" tester reading should closely match speedometer reading.

1. Code 24 will set if vehicle speed equals zero MPH when the engine speed is between 1200-4400 RPM, TPS is less than 2 percent (closed throttle), a low load condition (high vacuum) exists and all conditions met for 5 seconds. These conditions are met during a road load deceleration. Disregard Code 24 that sets when vehicle is not in motion.
2. If 8-12 volts is indicated at IP connector, circuit Yellow 03 is open between IP connector and the VSS, or there is a faulty vehicle speed sensor. A voltage of less than one volt at the IP connector indicates that circuit Yellow 03 is shorted to ground. If, after disconnecting circuit Yellow 03 at the vehicle speed sensor, voltage reads greater than 10 volts, vehicle speed sensor is faulty. If voltage remains less than 8 volts, check circuit Yellow 03 for short to ground. If circuit No. Yellowe 03 is not grounded, there is a faulty connection at ECM, or ECM is faulty.