OBD-II Code · Sensors
P0502
VSS Low Input
Severity
medium
Worth booking. It costs fuel, emissions or comfort until it is fixed.
Can you drive it
Only if running normally
A short trip to a shop may be reasonable if the light is steady and the car runs normally. Stop safely for a flashing light, severe shaking, overheating, loss of power, or another urgent warning. The code alone cannot confirm safety.
Indicative cost (USD)
$100–$300
Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.
VSS voltage low.
How a shop works this
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed.
Note every code that is set, not just this one.
Codes that appear together usually narrow the cause faster than any one of them read alone.
Read the freeze frame — the conditions the fault was recorded under.
Cold or warm, idle or load, road speed and engine speed. A fault that only appears cold is a different fault from one that only appears under load, even with the same code on the scanner.
Confirm the fault is current rather than history.
Clear the code and see whether it returns under those same conditions. A code that does not come back may have been logged during a repair, a flat battery, or a bad connection that has since been disturbed.
Then work the likely-causes list in the order shown.
That order is what a shop checks first for this code — wiring and connections before the component they run to, because a connector costs nothing to inspect and is a common answer.
If the code comes back after a repair, the underlying fault is still there. That is the point to bring in a scanner with live data and freeze-frame, or a shop that has one.
Common symptoms
- No speedo
Likely causes
- Failed sensorMost common
- Short to ground
Read the full diagnostic procedureP0502 means the VSS circuit is reading below the lowest allowable voltage or frequency, effectively a short-to-ground or open-circuit condition on th…
P0502 means the VSS circuit is reading below the lowest allowable voltage or frequency, effectively a short-to-ground or open-circuit condition on the signal wire, with the engine running and the vehicle expected to be moving. The PCM sees flatline 0 Hz when it should be seeing 100+ Hz.
Cheapest-first diagnosis
- key on engine off, back-probe the VSS signal wire with a DMM, you should see roughly 5V or 8V reference depending on sensor type when disconnected.
- With the sensor connected and the wheel spun by hand (vehicle safely raised), you should see the voltage pulse between roughly 0.3V and 4.7V on a Hall-effect sensor, or an AC waveform of 0.5V to 5V peak-to-peak on a variable-reluctance sensor.
- A flat 0V reading means a short-to-ground in the harness, while a flat 5V reading means an open in the signal return.
- Check the ground wire continuity to chassis next, this is a $0 fix if a ring terminal has corroded under a body bolt.
- The expensive misdiagnosis is replacing the PCM when the ground strap behind the cylinder head is loose.
Vehicle-specific patterns1996 to 2002 GM trucks with NV3500 manual transmission set P0502 from a failed VSS at the tailshaft, the sensor tip cracks from heat.
- 1996to 2002 GM trucks with NV3500 manual transmission set P0502 from a failed VSS at the tailshaft, the sensor tip cracks from heat.
- 2003to 2007 Nissan Frontier and Xterra set P0502 from a broken signal wire where the harness flexes near the transmission crossmember.
- 1998to 2004 Jeep Grand Cherokee WJ sets P0502 from the transfer case VSS connector filling with water from the cowl drain.
- 2000to 2005 Toyota Tacoma sets P0502 from rodent damage to the VSS harness routed along the frame rail.
Estimated repair$60 to $320.
Look up another code
P0502 — frequently asked
What does a P0502 code mean?
VSS voltage low.
What causes a P0502 code?
Common causes: Failed sensor; Short to ground.
What are the symptoms of a P0502 code?
Typical symptoms: No speedo.
Is it safe to drive with a P0502 code?
Only if running normally. A short trip to a shop may be reasonable if the light is steady and the car runs normally. Stop safely for a flashing light, severe shaking, overheating, loss of power, or another urgent warning. The code alone cannot confirm safety. Estimated repair: $100-$300.
How do I diagnose a P0502 code?
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed. 1. Note every code that is set, not just this one. 2. Read the freeze frame — the conditions the fault was recorded under. 3. Confirm the fault is current rather than history. 4. Then work the likely-causes list in the order shown.
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