Technical Description of OBD-II Trouble Code
Malfunction in Control Module VSS Output A
What does that signify?
This generic powertrain diagnostic trouble code (DTC) is applicable to various OBD-II vehicles, including but not limited to Citroen, Chevy, Ford, Peugeot, GMC, Dodge, Ram, Ducati, etc.
When a code P0608 is stored, it means that the powertrain control module (PCM) has detected a malfunction in a specific vehicle speed sensor (VSS) output voltage signal.
In this scenario, the PCM or one of the many other on-board controllers was expected to provide a VSS output signal. The specific VSS output circuit is designated as “A”. To understand the function of this circuit for the vehicle in question, consult a reliable source of vehicle information.
Vehicles equipped with OBD-II diagnostic systems may have up to seventy on-board controllers that communicate through the controller area network (CAN).
The VSS is an electromagnetic sensor that completes a circuit, providing an accurate signal of the vehicle speed to one or more controllers. It is usually located near the transmission output shaft, 4WD transfer case, or rear differential. The circuit is completed by a toothed, steel reluctor that passes close to the sensor, creating interruptions in the circuit. The PCM and other controllers interpret these interruptions as a wave form pattern of voltage, which represents the vehicle speed.
The VSS signal is typically input to a primary controller such as the PCM or transmission control module (TCM), which then shares it with other controllers through the CAN. If any of these secondary controllers fail to receive or receive an inconsistent VSS signal, a code P0608 will be stored and the malfunction indicator lamp (MIL) may illuminate.
Example photo of a VSS (Vehicle Speed Sensor):
What is the severity of this DTC?
VSS related codes can impact transmission shift strategy and engine drivability. A stored code P0608 should be considered severe and diagnosed/repaired promptly.
What are some of the symptoms of the code?
Symptoms of a P0608 trouble code may include:
What are some of the common causes of the code?
Possible causes for this code include:
What are some P0608 troubleshooting steps?
If there are any other VSS related codes stored, they should be diagnosed and repaired before attempting to diagnose the P0608.
To diagnose this code, you will need a diagnostic scanner, a digital volt/ohmmeter, and a reliable source of vehicle information.
Use the vehicle information source to search for technical service bulletins (TSB) that are relevant to the specific vehicle, the stored code, and the exhibited symptoms. If you find an applicable TSB, it is likely to provide helpful diagnostic information.
Refer to the vehicle information source for diagnostic flow charts, wiring diagrams, connector pin-out charts, connector face views, and component testing procedures/specifications. All this information is necessary for a successful diagnosis.
After visually inspecting the controller connectors and visible CAN harnesses, connect the scanner to the vehicle diagnostic port and retrieve all stored codes. If freeze frame data is available, make note of it as well. Clear the codes and test drive the vehicle until the PCM either enters readiness mode or the code is reset.
If the PCM enters readiness mode without any codes being stored, it indicates an intermittent code and the problem that contributed to it may need to worsen before an accurate diagnosis can be made.
If the code is reset, continue with the diagnosis.
Warning: Before using the DVOM to test circuit resistance and continuity, disconnect all related controllers to avoid controller damage.
With the key on and the engine off, use the DVOM to test individual VSS output circuits at the appropriate controller. Compare your findings with VSS signal data. If no acceptable output signal is detected, suspect controller failure.
If an acceptable VSS output signal is discovered at the controller, use the DVOM to test individual circuits between each of the related controllers. Repair or replace system circuits or components as required and retest the VSS signal.
