| DTC Data Sheet | |
| System | Powertrain |
| Standard | SAE J2012 / ISO 15031-6 |
| Fault type | Circuit Low |
| Official meaning | Vehicle Speed Sensor "A" Circuit Low Input |
The VSS signal voltage is below the expected minimum — typically a short to ground, open in the signal return, or a dead sensor.
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P0502 Quick Answer
The VSS signal voltage is below the expected minimum — typically a short to ground, open in the signal return, or a dead sensor.
What Does P0502 Mean?
Vehicle Speed Sensor "A" Circuit Low Input. The VSS signal voltage is below the expected minimum — typically a short to ground, open in the signal return, or a dead sensor.
Symptoms
- Speedometer reads zero
- Transmission defaults to a fail-safe shift schedule
- Cruise control disabled
- Check engine light
Common Causes
- Open VSS signal circuit (broken wire, disconnected connector)
- Short-to-ground on the signal wire
- Failed VSS (open coil)
- Loss of sensor power on platforms with a powered VSS
Diagnosis Steps
You’ll need a scan tool capable of reading live powertrain data, a digital multimeter, and access to the wiring diagram for the specific platform.
- Disconnect the VSS connector, key on, measure signal-wire voltage at the harness — should sit at 5 V or 12 V depending on platform. Zero or near-zero confirms an open or short.
- Continuity-check the signal wire from the connector to the PCM/ABS module pin.
- Resistance-check the VSS coil if applicable.
Possible Fixes
- Replace VSS
- Repair open or shorted wiring
- Connector pin repair
Can I Still Drive With P0502?
The vehicle will usually still drive with P0502 stored, but performance, drivability, or emissions will be degraded. The PCM may inhibit emissions monitors and limit closed-loop fueling adjustments. Drive to a workshop, but don’t ignore the code long-term.
How Serious Is This Code?
P0502 is a moderate-priority fault. It will not prevent the engine from running, but unaddressed it can cascade into related faults or damage downstream components such as the catalytic converter. Address within a few drive cycles.
FAQ
Will P0502 clear itself?
Only if the underlying fault was intermittent and self-corrected. Most root causes are persistent and require physical repair.
Can I clear P0502 without fixing it?
You can clear it with a scan tool, but it will return as soon as the fault condition reappears — typically within one or two drive cycles.
Is P0502 related to other codes?
Often, yes. Adjacent codes in the same circuit or system frequently set together — if P0502 is present, scan for related codes and address them as a group.