What Does P0608 Mean?
P0608 indicates a malfunction in the ECM/PCM Vehicle Speed Sensor (VSS) Output 'A' circuit. The ECM provides a vehicle speed signal output to other modules such as the cruise control module, ABS controller, or instrument cluster. This code sets when the ECM detects that its speed output signal is not functioning correctly. The driver may notice the speedometer not working, cruise control inoperative, or erratic shifting in automatic transmissions.
Common Causes
30%
ECM internal fault in the VSS output driver circuit
30%
Wiring fault in the VSS output circuit — open, short to ground, or short to power
20%
Failed vehicle speed sensor providing no input to the ECM for processing
12%
Receiving module fault creating a load issue on the VSS output circuit
8%
Corroded ground connection affecting the VSS output circuit reference
Diagnostic Steps
1
With the vehicle running in gear (wheels spinning on a lift or during road test), use an oscilloscope or frequency counter on the ECM VSS output pin to verify a speed-proportional signal is present — expect a square wave with frequency increasing with speed.
2
Backprobe the VSS output wire at the ECM connector and at the receiving module connector. With the vehicle moving, both points should show identical signals. A signal at the ECM but not at the receiver indicates a wiring fault.
3
Inspect the VSS output circuit wiring for damage, chafing, shorts, or corrosion. Measure resistance end-to-end (should be below 5 ohms) and check for shorts to ground or battery voltage.
4
Verify the ECM is receiving a valid VSS input signal first — check the vehicle speed PID on the scan tool. If the ECM shows 0 mph while the vehicle is moving, the input VSS is the problem, not the output.
5
If the input signal is good but no output is present at the ECM output pin, the ECM's internal output driver has failed and the module needs replacement.
Estimated Repair Cost
$100 - $1,200
Parts + labor, varies by vehicle and location
P0608 indicates a malfunction in the ECM/PCM Vehicle Speed Sensor (VSS) Output 'A' circuit. The ECM provides a vehicle speed signal output to other modules such as the cruise control module, ABS controller, or instrument cluster. This code sets when the ECM detects that its speed output signal is no...
The most common cause of P0608 (Control Module VSS Output "A" Malfunction) is: ECM internal fault in the VSS output driver circuit
Typical repair costs for P0608 range from $100 to $1,200, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Drive with caution. Loss of the VSS output can affect cruise control, transmission shift quality, and ABS operation. The speedometer may be inaccurate or inoperative. Avoid highway driving and be aware that the ABS may not function correctly until the fault is repaired.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0608 to identify the root cause.
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Quick Info
Category
Powertrain
System
Vehicle Speed / Electronic Controls
Difficulty
Type
Generic (SAE)
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