P0502
Vehicle Speed Sensor A Circuit Low
Vehicle speed / powertrain control
Generic OBD-II
High
What it means
P0502 means the vehicle speed sensor (VSS) signal is abnormally low or missing. Many systems depend on this signal — speedometer, odometer, cruise control, transmission shift timing, and often ABS/traction control — so a lost signal causes a cluster of symptoms. The usual causes are a failed sensor or a wiring short/open in its circuit.
High
Can I keep driving? Drivable but degraded — the speedometer, cruise control, and transmission shifting rely on this signal, so expect erratic shifts and lost cruise. Have it fixed promptly.
Common symptoms
What you'll notice
- Check-engine light on
- Inaccurate or dead speedometer/odometer
- Harsh, erratic, or delayed transmission shifts
- Cruise control disabled
- ABS or traction-control warning light (shared speed data)
Common causes
Most likely first
- Failed vehicle speed sensor (low or no signal)Likely
- Short to ground or open in the sensor signal wiringCommon
- Loose or corroded connector at the sensorCommon
- Damaged sensor reluctor/tone ringLess often
- ECM/PCM fault (rare)Less often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and confirm the code with a scan tool.
- Inspect the speed sensor connector and wiring for a short to ground or open.
- Check the sensor and its tone ring for damage or debris.
- Back-probe the signal while turning the wheel/driveline and watch for a reading.
- Replace the speed sensor if it produces no valid signal. Clear and re-test.
FAQ
Quick answers
Is it safe to drive with P0502?+
It runs, but the speedometer, cruise, and shifting can misbehave, and ABS/traction may drop out. Drive carefully and fix it soon.
Can I just clear P0502?+
It returns until the sensor or wiring is repaired. The transmission and speedometer need a valid speed signal.
Related codes
Often seen with P0502
Read & clear P0502 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