Code 21 Speed Sensor Circuit: Notes

Speed sensor rotor shaft is driven by a gear on Electronically Controlled Transmission (ECT) output shaft. For each shaft rotation, speed sensor sends a 20-pulse signal to the instrument cluster. This signal is converted inside the instrument cluster to a 4-pulse signal and is sent to cruise control ECU. Cruise control ECU calculates vehicle speed from this pulse frequency. Code 21 is set when 4-pulse signal from instrument cluster is not received by the cruise control ECU.