Error code

OBD2 P0418

OBD2P0418
Diagnostic Trouble Code· Standard OBD-II fault code read from the vehicle's onboard diagnostics.

What it means

Secondary Air Injection System Control 'A' Circuit.

Severity

moderateCan drive but may fail emissions tests.

Summary

P0418 indicates a malfunction in the Secondary Air Injection System Control 'A' circuit, specifically related to relay A and its associated wiring or components.

Symptoms

  • Stored trouble code
  • Illuminated warning light
  • Potential failure during emissions testing

Common Causes

  • Defective relay A
  • Damaged, shorted, disconnected, or corroded wiring and/or connectors
  • Blown fuses or fusible links
  • Failed AIS pump/motor
  • Water ingress causing freezing of the SAI pump

Diagnosis

  1. Record all fault codes and freeze frame data.
  2. Inspect wiring harness for damage, including fuses and fusible links.
  3. Test relay A's operation and internal resistance.
  4. Perform continuity checks on associated wiring.
  5. Check SAI pump’s internal resistance and current draw.

Fixes

  • Replace defective relay or damaged wiring/connectors.
  • Replace blown fuses/fusible links if no short circuits are found.
  • Replace failed AIS pump/motor if resistance and current draw tests indicate failure.

FAQ

Can I drive with P0418?

Yes, but the vehicle may fail emissions testing.

What causes P0418?

Common causes include a faulty relay A, damaged wiring/connectors, blown fuses/fusible links, and failed AIS pump/motor.

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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