Code 21 Or 23: (Speed Sensor Circuit)

Code 21 sets if the cruise control ECU does not receive a speed signal from the instrument cluster. Code 23 sets if speed sensor circuit is open intermittently, or if vehicle speed decreases to at least 10 MPH (16 KM/H) less than set speed.

1. Check if cruise control ECU is receiving input signal from speed sensor (instrument cluster). See INPUT SIGNAL CIRCUITS  under CIRCUIT TESTING. If input signal circuit is not okay, go to next step. If input signal circuit is okay:
   • CODE - Replace cruise control ECU
   • NO CODE - Perform next procedure listed in the DIAGNOSIS BY SYMPTOM  table.
2. Check if speedometer operates. Repair speedometer if it does not operate. See INSTRUMENT PANEL article in the ACCESSORIES/SAFETY EQUIPMENT section. If speedometer operates, check for faulty circuit between instrument cluster and cruise control ECU. If circuit is okay, replace cruise control ECU.