P0608 is set when the powertrain control module (PCM) detects an abnormal or missing vehicle speed sensor (VSS) output signal. The code indicates that the PCM is not receiving the expected VSS data from its own output circuit or from the VSS sensor, which can affect speedometer operation and related systems.
The VSS itself may have failed internally, producing no signal or an erratic waveform that the PCM cannot interpret.
Corrosion, chafed wires, or loose pins between the VSS sensor and the PCM can interrupt the signal path.
An inadequate ground or voltage supply can cause the sensor to output a weak or absent signal.
The internal transistor or driver circuit within the PCM that generates the VSS output may be defective, though this is less common than sensor or wiring issues.
A malfunction inside the PCM that prevents it from processing the VSS signal is possible but uncommon; other causes should be ruled out first.
No. While a faulty PCM can cause this code, it is rare. Most P0608 cases are due to a bad VSS sensor, wiring issues, or poor grounds. PCM replacement should only be considered after those components have been verified as functional.
Indirectly. If the speedometer failure is due to a missing VSS signal, the underlying cause is usually the sensor or its circuit, not the gauge itself.
Clearing the code only turns off the Check Engine Light; if the root cause remains, the code will return once the PCM detects the abnormal VSS output again.