What P0418 means
After a cold start the secondary air (AIR) pump blows fresh air behind the exhaust valves so that unburnt fuel burns off and the catalyst heats up faster; a shut-off valve opens the path and stops exhaust from flowing back.
How the engine computer detects it
Control A is the drive circuit of pump A – in practice the coil of the pump relay, which the module switches to ground; the old wording was Relay A. GM uses P0418 for an open circuit (200 kΩ or more, 20 of 25 samples, MIL after two trips) and P2257/P2258 for shorts; Saab and Toyota describe the same circuit. If the pump does not run, P0411 may follow. A relay with welded contacts keeps the pump running – Subaru recalled cars because the pump could overheat.
Written from public technical sources and not yet checked by a mechanic. How we write these pages
Symptoms
- Check engine light on
- Pump does not run after a cold start – or runs constantly if the relay is welded
- Secondary air readiness not set (emission test)
- Hot pump or burning smell if it runs constantly
Common causes
- Pump relay faulty (coil open, contacts burnt or welded) Most likely
- Control wire or connector to the relay open or corroded Most likely
- Fuse blown, often due to a seized pump Possible
- Pump stiff or blocked by water or debris Possible
- Driver in the engine module Less likely
How to diagnose P0418
- Read every stored code with an OBD-II scanner. If misfire or fuel trim codes are there too, fix those first: they often cause this one.
- Inspect the parts involved: air pump relay, secondary air pump, relay wiring, engine control module.
- Work through the causes above from most to least likely, cheapest checks first.
- Clear the code and drive a full drive cycle to confirm the repair held.
Vehicles that report P0418 most
| Vehicle | Years | Reports | Share | Median miles |
|---|---|---|---|---|
| Toyota Tundra | 2007–2013 | 10 | 87k |
Counts of owner complaints to the NHTSA that mention P0418 (16 in total), not failure rates: popular models get more complaints simply because more of them are on the road. Models with fewer than 3 complaints are left out.
Reading the code
- P
- Powertrain
- 0
- Generic (SAE) code
- 4
- Auxiliary emission controls
- 18
- Specific fault
Questions drivers ask
Can I drive with code P0418?
Usually yes for a short time, if the car drives normally, the temperature gauge reads normal and the check engine light is steady. If the light flashes, the engine loses power or overheats, or other warning lights come on, pull over and have it checked.
Will my car pass an emissions inspection with P0418?
Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.
Will P0418 clear by itself?
The light can go off after several drive cycles without the fault, but the code returns if the cause is still there. After a repair, the readiness monitors need a full drive cycle before an inspection.
Can I fix P0418 myself?
Often yes, with an OBD-II scanner and basic tools. Difficulty: easy. Start with the cheapest checks before replacing expensive parts.
Often reported together
Codes that owners mention in the same NHTSA complaints as P0418. They can point to a shared cause, so it's worth checking them together.
- P2441Secondary Air Injection System Switching Valve Stuck Closed (Bank 1)4 complaints
- P2440Secondary Air Injection System Switching Valve Stuck Open (Bank 1)3 complaints
- P2442Secondary Air Injection System Switching Valve Stuck Open (Bank 2)3 complaints
This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.