DTC code
P0418
AIR System Control A Circuit
Technical guide
Symptoms
- Illuminated check engine light (MIL)
- rough idle
- engine hesitation on acceleration
- stalling at startup or at idle
- abnormal noise from the SAI pump/components
- increased emissions and likely emissions test failure. The code often does not affect normal drivability since the system mainly runs during cold starts.
Probable causes
- Faulty SAI pump relay (most common per sources)
- damaged
- corroded or burnt wiring and connectors in the relay control circuit
- blown fuse from an overloaded circuit
- faulty SAI air pump
- water entering the system through a faulty one-way check valve (often in cold weather)
- damaged hoses or fittings.
Diagnostic steps
- Connect a scan tool, confirm P0418 and note any related SAI codes and freeze frame data.
- Visually inspect the SAI relay, fuse, wiring and connectors for damage, corrosion or heat damage from exhaust; check connector pins.
- With a digital volt/ohmmeter, verify power and ground at the relay and check circuit continuity.
- Use the scan tool actuator test (if available) to command the relay/pump on and confirm operation.
- Inspect the one-way check valve for water intrusion and the hoses/fittings for cracks; replace faulty check valves, relay, wiring or blown fuses as found (if a fuse is blown, retest for recurrence).
- Clear the code and test drive with a cold start to verify the fault does not return.
Cross-checked technical synthesis (QA). It does not replace the manufacturer's procedure.
Models most reported with this code (NHTSA)
Count of distinct owner complaints mentioning the code. US data — same engines, same failures.
AI here is a librarian: this page shows only what mechanics confirmed, or says “unknown”. It never suggests a diagnosis — MECCANIC interprets the code, never your car.
0 confirmed cases on P0418
Nothing confirmed yet for this code. No guess is offered on purpose.
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