P0418: Secondary Air Injection System Control A Circuit
What to do
Driveable with no symptom you would notice, though you may notice the absence of the usual whirring noise after a cold start. Will fail an emissions test.
What this code means
A fault in the circuit controlling the relay that powers the secondary air pump. The pump draws a large current — far more than a module output can supply directly — so it is switched by a relay, and this code concerns the low-current control side rather than the pump itself.
The relay is worth testing before the pump on any secondary air complaint, because it is dramatically cheaper and fails at least as often. A pump that never runs and a relay that never closes present identically to a driver.
Likely causes
Start here
Less common
- Broken wire in control circuit · moderate
- Corroded relay socket · easy
Rare
- Control module driver failure · specialist
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
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