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EmissionsSeverity Low: usually safe to drive

P0418Secondary Air Injection System Control "A" Circuit

What it means

The ECU sees an electrical fault in the circuit that switches the secondary air pump (usually its relay).

Symptoms

  • Check engine light
  • Sometimes a whining or roaring noise from the air pump after a cold start
  • Usually no change in how the car drives

Common causes

  • Faulty air pump relay
  • Wiring fault
  • Pump drawing too much current (seized)

What to check first

  1. Check the relay and fuse
  2. Check the relay control from the ECU
  3. Measure the pump current
Can I drive with P0418? Usually yes. P0418 rarely affects how the car drives, but it keeps the check engine light on and can fail an emissions test.

Generic OBD-II meaning. Manufacturer-specific meanings and checks can differ; always check the service information for the car.

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P0418: questions and answers

What does P0418 mean?

P0418: Secondary Air Injection System Control "A" Circuit. The ECU sees an electrical fault in the circuit that switches the secondary air pump (usually its relay).

What are the symptoms of P0418?

Check engine light. Sometimes a whining or roaring noise from the air pump after a cold start. Usually no change in how the car drives.

What causes P0418?

Faulty air pump relay. Wiring fault. Pump drawing too much current (seized).

How do you diagnose P0418?

1. Check the relay and fuse 2. Check the relay control from the ECU 3. Measure the pump current

Can I drive with P0418?

Usually yes. P0418 rarely affects how the car drives, but it keeps the check engine light on and can fail an emissions test.