Code 21 Or 23 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. Code 23 is set when speed sensor circuit is open intermittently or when vehicle speed decreases to at least 10 MPH (16 Km/h) below set speed.