Error code

OBD2 P0502

OBD2P0502
Diagnostic Trouble Code· Standard OBD-II fault code read from the vehicle's onboard diagnostics.

What it means

Vehicle Speed Sensor 'A' Circuit Low Input.

Severity

moderateCan drive but may experience erratic behavior and safety system deactivation.

Summary

P0502 indicates a low input signal from the primary vehicle speed sensor (VSS), typically located near the transmission's output shaft.

Symptoms

  • Erratic or incorrect operation of the speedometer/odometer
  • Harsh, erratic, or unpredictable gear shifts
  • Unexpected activation/deactivation of safety systems like ABS
  • Additional codes related to transmission, cruise control, traction control, and stability control

Common Causes

  • Damaged, burnt, shorted, disconnected, or corroded wiring and connectors
  • Defective speed sensors including damage to reluctor rings
  • Excessive metal wear particles or debris affecting sensor operation
  • Failed PCM or other relevant control module (rare)

Diagnosis

  1. Record all fault codes and freeze frame data.
  2. Inspect wiring and connectors for damage, repair or replace as needed.
  3. Perform resistance, continuity, ground, and reference voltage tests on associated wiring.
  4. Monitor sensor operation in real-time using a scanner to compare with speedometer readings.

Fixes

  • Replace damaged wiring/connectors or defective vehicle speed sensor.

FAQ

What causes P0502?

Common causes include faulty wiring, connectors, debris affecting sensors, and rare cases of PCM failure.

How do I diagnose P0502?

Diagnose by inspecting wiring/connectors, performing electrical tests, and monitoring sensor operation with a scanner.

View source

Not affiliated with OBD2. Answer summarized from the manufacturer's manual linked above; consult that source for the authoritative procedure.

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