P0608
Control Module VSS Output A
Vehicle speed signal output
Generic OBD-II
High
What it means
P0608 means the control module (ECM/PCM) has detected a fault with its vehicle-speed-signal output "A" — the speed value it passes on to systems like the speedometer, cruise control, and transmission. The engine itself usually still runs, but downstream systems that rely on that signal can misbehave. The cause is typically the output wiring, a bad speed-sensor input, or an internal module fault.
High
Can I keep driving? Usually drivable, but treat it seriously — a faulty speed-signal output can upset the speedometer, cruise control, and shift timing, which is a safety concern.
Common symptoms
What you'll notice
- Check-engine light on
- Erratic or dead speedometer
- Cruise control won't work
- Harsh or incorrect shifting on some vehicles
Common causes
Most likely first
- Wiring or connector fault between the control module and the systems that receive the speed signalLikely
- Short or open on the VSS output A circuitCommon
- Faulty vehicle speed sensor feeding the moduleCommon
- Internal control-module (ECM/PCM) faultLess often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and check the VSS output A circuit for shorts, opens, and loose connectors.
- Verify the vehicle speed sensor input is good before suspecting the output side.
- Compare the module's speed output against actual road speed with a scan tool.
- Repair wiring faults; if the circuit checks out, the internal module fault points to ECM/PCM service. Clear and re-test.
FAQ
Quick answers
Is it safe to drive with P0608?+
It's usually driveable, but a wrong or missing speed signal can disable cruise, confuse the transmission, and give a false speedometer — so get it diagnosed promptly.
Can I just clear P0608?+
It'll return until the circuit or module fault is repaired. Clear it after the fix to confirm the speed signal is stable.
Related codes
Often seen with P0608
Read & clear P0608 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX