P0418 Generic (SAE) Basic entry

Secondary Air Injection System Control 'A' Circuit

Updated 2026-10-02 · Auxiliary emission controls

Severity

Medium

Typical repair cost

60 – 500 EUR

System

Powertrain

What it means

P0418 is defined as "Secondary Air Injection System Control 'A' Circuit". the engine control module stores it when the monitored condition for this component or system is outside the limits programmed by the manufacturer.

This entry is compiled automatically from the standard definition and typical diagnostic practice for this type of fault. A detailed, reviewed article is in preparation.

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Symptoms

Check engine light on, often with no change in driveability
Failed emissions inspection
Slight increase in fuel consumption
Smell from the exhaust in some cases

Common causes

Secondary Air Injection System Control 'A' Circuit worn, contaminated or out of calibration
Mechanical problem in the system the sensor measures
Air, vacuum or exhaust leak influencing the reading
Wrong or low-quality replacement part
Wiring resistance causing a small voltage offset

How to diagnose

Compare the live Secondary Air Injection System Control 'A' Circuit reading with a known-good value or a second sensor at idle and at 2500 rpm
Check for air, vacuum or exhaust leaks that could skew the reading
Inspect the component for contamination and clean it if the design allows
Verify the part number is correct for the engine
Replace the Secondary Air Injection System Control 'A' Circuit if the reading remains out of specification

Frequently asked questions

Can I keep driving with P0418?

Usually yes for a short time, but expect reduced performance or higher fuel use. Have it diagnosed within a few days.

Will clearing P0418 fix it?

No. Clearing only erases the stored code; it returns as soon as the monitor runs again unless the cause is repaired.