Vehicle Speed Sensor A Signal Transmission Error
Indicates there is a problem with the vehicle speed sensor signal.
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What it means (plain English)
The vehicle speed sensor (VSS) sends signals to the computer about how fast the vehicle is moving. If that signal is weak or not operating, the computer can't track speed properly, affecting transmission and engine management.
What the computer is actually seeing
The Electronic Control Unit (ECU) expects a stable signal from the VSS, usually a square wave of 0 to 5 volts. If it gets no signal or the signal is erratic, it triggers this code.
What a healthy reading looks like
A functional VSS should provide a frequency signal proportional to vehicle speed, typically around 0-5 volts fluctuating at a rate proportional to speed (e.g., 2.5 volts at 30 mph).
Guided diagnostic — the DiagCoach way
Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.
- 11. Check vehicle speed: Verify if the speedometer is working. If it’s not, proceed to the next step.
- 22. Inspect wiring: Look for damaged, frayed, or corroded wires leading to the VSS.
- 33. Check connectors: Ensure the VSS connector is secure and free of corrosion or dirt.
- 44. Test VSS output: Using a multimeter, check for voltage output from the VSS while the wheel is turning. Expect a 0-5V signal.
- 55. Replace VSS if faulty: If the VSS does not produce proper voltage, replace it and clear the code. If the circuit is good, look for ECU issues.
Common causes
- Faulty vehicle speed sensor (VSS)
- Wiring issues (frayed or broken wires) in the VSS circuit
- Dirty or corroded connectors at the sensor or ECU
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with SPN 6155?
It's moderate severity; drivability could be affected. Fix this soon.
Will the code come back after replacing the VSS?
If the wiring and connectors are good and the replacement is done correctly, it should not.
Why does this code sometimes pair with other codes?
Related codes can indicate system-wide issues, such as from speed-related faults or transmission problems.
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