P0418: Secondary Air Injection System Control 'A' Circuit
Diagnostic trouble code P0418 — what it means, the common
causes, and how to confirm the real fault before replacing parts.
What does P0418 mean?
P0418 indicates: Secondary Air Injection System Control 'A' Circuit.
This relates to the Emissions / auxiliary emission controls system.
Common causes of P0418
Secondary Air Injection Solenoid Valve N112 or N320 malfunction
Secondary Air Injection Pump Motor V101 failure
Restricted flow in the secondary air system (e.g. ingress of dirt downstream of pressure sensor causing increased pressure level)
Leak in the secondary air system upstream of the pressure sensor causing decreased pressure level
Moisture/water ingress into the vacuum system damaging solenoid valve components
Interchanged connectors or hoses on secondary air injection valves
Combination valve (vacuum controlled) failure
What to check (live data)
Secondary Air Injection Sensor 1 G609 pressure signal (compared with ambient pressure sensor and intake manifold pressure sensor signals during Phase 0 at ignition on)
Pressure level from G609 — increased pressure indicates restricted flow downstream of sensor; decreased pressure indicates restriction upstream of sensor or a leak
Oxygen sensor signals during secondary air injection measurement phase (compared against threshold values by ECM)
Parts often involved in P0418
Secondary Air Injection Solenoid Valve N112
Secondary Air Injection Solenoid Valve 2 N320
Secondary Air Injection Pump Motor V101
Secondary Air Injection Sensor 1 G609
Combination valve 1 (vacuum controlled)
Combination valve 2 (vacuum controlled)
Vacuum pump
Water separator / filter elements in vacuum hoses
Resonator
Don't replace parts until the root cause is confirmed — many of these codes are caused by wiring, a connector or an upstream fault, not the part itself.
Get the confirmed root cause for P0418 — on YOUR vehicle
A code is a symptom, not a diagnosis. AutoDX Pro cross-checks several
independent assessments, pinpoints the actual root cause, gives you the
exact tests to confirm it, and shows the parts — only after the cause is
confirmed. Reads your scan-tool photo and decodes your VIN with open
recalls.
P0418 is a diagnostic trouble code: Secondary Air Injection System Control 'A' Circuit.
What are the common causes of P0418?
Common causes include: Secondary Air Injection Solenoid Valve N112 or N320 malfunction, Secondary Air Injection Pump Motor V101 failure, Restricted flow in the secondary air system (e.g. ingress of dirt downstream of pressure sensor causing increased pressure level), Leak in the secondary air system upstream of the pressure sensor causing decreased pressure level. The exact cause depends on the vehicle — confirm it before replacing parts.
Can I keep driving with P0418?
It depends on the fault and your symptoms. Some causes are minor, others can damage components or affect safety. Get the root cause confirmed before deciding.
How do I fix P0418?
Confirm the actual root cause with targeted tests first, then replace only the part that's at fault. AutoDX Pro gives you the root cause, the exact tests, and the parts for P0418 on your specific vehicle.