P0509 – Idle Air Control Circuit High

Description

The ECM detects a high voltage signal in the idle air control circuit.

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Symptoms

  • High idle
  • Surging
  • Poor fuel economy

Causes

  • Open circuit
  • Faulty IAC valve
  • Wiring issues

Diagnosis

  • Monitor IAC voltage
  • Inspect wiring
  • Check valve operation

Repair

  • Repair wiring
  • Replace IAC valve

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