Code 24 - Vehicle Speed Sensor ("F" Body): Notes

The ECM applies and monitors 12 volts on circuit No. 437. Circuit No. 437 connects to the vehicle speed sensor which alternately grounds circuit No. 437 when vehicle is in motion. This pulsing action takes place about 2000 times per mile and the ECM will calculate vehicle speed based on the time between "pulses".

With vehicle in motion, the "SCAN" tester reading should closely match with speedometer reading. Disregard a Code 24 set when vehicle is not in motion.

1. Code 24 will set if vehicle speed equals zero mph when the following conditions occur:
   • Engine speed is between 1200-4400 rpm.
   • TPS is less than 2% (closed throttle).
   • Low load condition (high vacuum). Less than 8 psi (2.5 kg/cm² ).
   • All conditions met for 5 seconds. If these conditions are met during a road load deceleration, disregard Code 24 that sets when vehicle is not in motion.
2. When there is 8-12 volts at the IP connector, this indicates circuit No. 437 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 No. 437 is shorted to ground. If, after disconnecting circuit No. 437 at the vehicle speed sensor, the voltage reads above 10 volts, the vehicle speed sensor is faulty. If voltage remains less than 8 volts, then circuit No. 437 is grounded. If circuit No. 437 is not grounded, there is a faulty connection at the ECM, or a faulty ECM unit.