P0418
Secondary Air Injection System Control "A" Circuit
- Severity
- Low
- Driving
- Drivable — book it in
A fault in secondary air injection control circuit "A" - typically the circuit that switches the air pump itself, through its relay. Without it the pump will not run, so the system does nothing on a cold start.
Possible causes
- CommonFailed air pump relay
- CommonCorroded relay socket or fuse box connections
- CommonWiring fault between the module and the relay
- CommonBlown fuse on the pump circuit
- PossibleSeized pump drawing excessive current and taking out the circuit
- RareFailed control module driver
What you might notice
- No pump noise on a cold start
- Check engine light on
- Failed emissions test
- Blown fuse, sometimes repeatedly
- Usually no symptom the driver notices
What to check, in order
- Check the fuse and swap the relay with an identical one elsewhere in the box. Both cost nothing and account for a large share of these faults.
- Listen on a cold start to confirm whether the pump runs at all.
- Inspect the relay socket for corrosion and heat damage.
- If a fuse keeps blowing, suspect a seized pump. A pump that has ingested water draws far more current than the circuit is designed for.
- Check the wiring between the module and the relay.
Read this code from your own car
Plug an ELM327 adapter into the OBD-II port under the dashboard. Pin16 reads every stored, pending and permanent code, explains each one like this page does — offline, with no account — and shows what the car recorded when the fault was set.
Where this code sits
P00xxP01xxP02xxP03xxP04xxP05xxP06xxP07xxP08xxP09xxP0AxxP0BxxP0CxxP0DxxP0ExxP0FxxP10xxP11xxP12xxP13xxP14xxP15xxP16xxP17xxP18xxP19xxP1AxxP1BxxP1CxxP1DxxP1ExxP1FxxP20xxP21xxP22xxP23xxP24xxP25xxP26xxP27xxP28xxP29xxP2AxxP2BxxP2CxxP2DxxP2ExxP2FxxP30xxP31xxP32xxP33xxP34xxP35xxP36xxP37xxP38xxP39xxP3AxxP3BxxP3CxxP3DxxP3ExxP3Fxx
Auxiliary emission controls
P0400P0401P0402P0403P0404P0405P0406P0407P0408P0409P0410P0411P0412P0413P0414P0415P0416P0417P0418P0419P0420P0421P0422P0423P0424P0425P0426P0427P0428P0429P0430P0431P0432P0433P0434P0435P0436P0437P0438P0439P0440P0441P0442P0443P0444P0445P0446P0447P0448P0449P0450P0451P0452P0453P0454P0455P0456P0457P0458P0459P0460P0461P0462P0463P0464P0465P0466P0467P0468P0469P0470P0471P0472P0473P0474P0475P0476P0477P0478P0479P0480P0481P0482P0483P0484P0485P0486P0487P0488P0489P0490P0491P0492P0493P0494P0495P0496P0497P0498P0499