P0418: Secondary air injection relay A circuit malfunction
The ECU sees a fault in the circuit of the relay that powers the secondary air pump. It is usually the relay itself, a fuse or the wiring.
| Code | P0418 |
|---|---|
| System | Engine and transmission |
| Group | P04xx, Emissions control |
| Type | Generic: it means the same on every make |
| Can you keep driving? | Yes, no rush |
What P0418 means
The secondary air pump draws a lot of current, so the ECU switches it on through a relay. It has detected that the relay control circuit is not responding properly. If the relay sticks on, the pump may run constantly and burn out.
Most common causes
- Faulty or stuck secondary air pump relay
- Blown fuse in the circuit
- Corroded relay or pump connector
- Relay control wiring broken or shorted
- Shorted pump damaging the relay
Symptoms
- Engine warning light on
- Pump does not run from cold
- Pump runs constantly, even when warm
- Failing an emissions test
Can you drive with P0418?
Yes, no rush You can drive. If you hear the pump running all the time, have it seen soon as it may burn out; otherwise there is no rush.
Open the bonnetthe in-depth explanation
How to check it
Listen to the pump: it should only run for the first minute after a cold start. If it never runs or never stops, swapping the relay for an identical one from the fuse box is a quick test a garage can do.
How to read and clear P0418 with Final OBD
Plug an OBD2 scanner in under the steering wheel, switch the ignition on and open Final OBD. Under Faults you’ll see P0418 with its description and whether it’s confirmed, pending or permanent.
If the engine stores it over standard OBD, with FREE you read this code with its explanation for nothing and clear it. With PRO you also read the faults of every control unit and clear them in all of them.
Clearing the code only turns the light off: if the cause is still there, it comes back. Clear it once it’s fixed, and not right before an inspection. It’s all in how to read and clear fault codes and in inspections and OBD.
Similar codes
- P0414 The secondary air injection system switching valve A has a short circuit
- P0415 The secondary air injection system switching valve B has an electrical fault
- P0416 The secondary air injection system switching valve B has a broken or
- P0417 The secondary air injection system switching valve B has a short circuit
- P0419 The secondary air injection system relay B has an electrical fault
- P041A The exhaust gas recirculation temperature sensor B has an electrical fault
- P041B The exhaust gas recirculation temperature sensor B gives readings outside the
- P041C The exhaust gas recirculation temperature sensor B gives a lower signal than
- P0400 Exhaust gas recirculation (EGR) flow malfunction
- P0401 Exhaust gas recirculation (EGR) flow insufficient
- P0402 Exhaust gas recirculation (EGR) flow excessive
- P0403 EGR control circuit malfunction
What does code P0418 mean?
The secondary air pump draws a lot of current, so the ECU switches it on through a relay. It has detected that the relay control circuit is not responding properly. If the relay sticks on, the pump may run constantly and burn out.
Can you drive with P0418?
You can drive. If you hear the pump running all the time, have it seen soon as it may burn out; otherwise there is no rush.
How do you clear P0418?
With an OBD2 scanner and an app like Final OBD, which clears it for free if it’s stored by the engine control unit. But clearing it only turns the light off: if the cause isn’t fixed, P0418 comes back.
Read it on your car
Final OBD reads and clears engine faults through standard OBD for free, each one explained in plain English. With PRO it also reads the faults of every control unit, each make’s own codes included, and clears them in all of them.
