1. Locate the VSS (Vehicle Speed Sensor) in the top rear of the transmission. The Yellow/Blue wire is battery voltage key on and the Black wire is ground. The Yellow/White wire is a 5-volt reference voltage from the control units.
2. Plugged in, the VSS should pulse the 5 volts on the Yellow/White wire to ground when the VSS is turning. Using a scan tool, watch the signal on the Yellow/White wire. If the signal is good, check the signal at the speedometer head and verify the connection. If the connection and signal are correct, look at a faulty speedometer head.
Vehicle Speed Sensor (VSS)
Some scanners will connect to this vehicle. If able to read vehicle speed on the scan tool test, then test for the speed signal right at the connector on the back of the speedometer. The wire is Yellow/Blue and is located in the 12-cavity Gray connector. Back probe the connector and test for a 0-5 volt square wave signal when driving. If the signal is good, check for powers and grounds, and look for a faulty speedometer head.