P0418 code meaning
AIR System Control A Circuit
Powertrain system Generic code P04xx codes Check engine light
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. 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.
P0418 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyEasy, DIY possible
- Typical labor0.2 to 2.5 hours
- Clears after repairAfter a drive cycle
Symptoms of P0418
- 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 (emissions test)
- Hot pump or burning smell if it runs constantly
Common causes of P0418
- Most likelyPump relay faulty (coil open, contacts burnt or welded)
- Most likelyControl wire or connector to the relay open or corroded
- PossibleFuse blown, often due to a seized pump
- PossiblePump stiff or blocked by water or debris
- Less likelyDriver in the engine module
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Air pump relaySecondary air pumpRelay wiringEngine control module
What each part of P0418 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 4 | Area: auxiliary emission controls (catalytic converter, EGR, EVAP). |
| 18 | The exact fault in that area. |
What to do next
- Note P0418 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0418
What does P0418 mean?
P0418 means "AIR System Control A Circuit". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P0418?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P0418 fail an emissions test?
Yes, it can. P0418 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0418 to fix?
Difficulty: easy. A typical repair takes 0.2 to 2.5 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P0418 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.