Dead Speedometer
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J,
Welcome Aboard!
The speedometers in our cars are electically driven, not mechanical. They require a working Vehicle Speed Sensor (VSS) to provide the pulsed signal to the speedometer and the vehicle's ECM for control information. The VSS on most of our cars is mounted in the tailshaft housing of the transmission.
Absence of this signal to the ECM will also set an error code after driving a short distance, and turn on the SES lamp on the dash. You can verify whether or not you have this problem by scanning the ECM for error codes. It is very easy, requiring no special tools, and takes about five minutes. If the ECM displays the error code for a failed VSS, you may have a problem with the electrical connector at the VSS, connections at the in-line buffer module for the VSS, or a failure of the sensor or driving gear itself (it is driven by a small plastic gear like the old mechanical speedometer cables). If there is no error code present, the ECM is receiving the correct signal and the speedometer is either NOT getting the signal or has malfunctioned. After determining that, you can decide whether or not to remove the speedometer for repair or replacement. Incidentally, there are electrical connections for the speedometer as well, so don't overlook those if you get that far in the diagnosis.
Welcome Aboard!
The speedometers in our cars are electically driven, not mechanical. They require a working Vehicle Speed Sensor (VSS) to provide the pulsed signal to the speedometer and the vehicle's ECM for control information. The VSS on most of our cars is mounted in the tailshaft housing of the transmission.
Absence of this signal to the ECM will also set an error code after driving a short distance, and turn on the SES lamp on the dash. You can verify whether or not you have this problem by scanning the ECM for error codes. It is very easy, requiring no special tools, and takes about five minutes. If the ECM displays the error code for a failed VSS, you may have a problem with the electrical connector at the VSS, connections at the in-line buffer module for the VSS, or a failure of the sensor or driving gear itself (it is driven by a small plastic gear like the old mechanical speedometer cables). If there is no error code present, the ECM is receiving the correct signal and the speedometer is either NOT getting the signal or has malfunctioned. After determining that, you can decide whether or not to remove the speedometer for repair or replacement. Incidentally, there are electrical connections for the speedometer as well, so don't overlook those if you get that far in the diagnosis.
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