2002 Chrysler Caravan Transmission Issues: P0720, P0730, P0721 Fault Codes and Speed Sensor Problems
I own a 2002 Chrysler Caravan and am experiencing a serious issue with the speedometer and transmission behavior. The speedometer now reads 20 mph while the vehicle is completely stopped at a traffic light, and I'm noticing harsh downshifts during driving. My OBD2 scanner shows persistent fault codes P0720, P0730, and P0721. I've already replaced both the input and output speed sensors, but the problem persists. The vehicle speed sensor (VSS) is still registering 20 mph even when the car is in park. I'm at a loss as to what could be causing this. Any insights or troubleshooting steps would be greatly appreciated?
When the vehicle is in park and the speedometer reads 20 mph, try disconnecting the alternator's electrical connector. If the speedometer drops to zero, this suggests a faulty diode inside the alternator is generating AC voltage. Since the VSS is an AC sensor, it can misinterpret this AC signal as actual vehicle speed. If the reading goes to zero after disconnection, it confirms the issue and you should take the car to an auto parts store for testing or replacement of the alternator.