P0418 Code Meaning and Next Steps

First checks take 10 to 20 minutes for the first checks. No special tools are usually needed for the first checks.

Can you keep driving?

Stop driving if any of these apply

!The engine starts running much worse, stalls, or the warning light flashes.
!The vehicle begins to overheat, knock, or lose power sharply while the code is active.

If the light is steady and the vehicle still drives normally: Often yes for a short time, but it should not be ignored.

What to check first

Step-by-step checks

1
Free - no tools
Let the exhaust cool before checking the pump relay and wiring
2
Free - no tools
Inspect the relay, fuse, and connector for heat damage or corrosion
3
Basic tool needed
Listen for the pump running at cold start if the vehicle normally does that
4
Basic tool needed
Check whether the code appeared after wet weather, a cold morning, or recent underhood work
5
Basic tool needed
If scan data is available, compare commanded relay operation with the actual pump response

If the code returns

-If the relay does not click or pass power, it rises to the top of the list.
-If the pump runs on direct power but not through the relay, the relay or command side is more likely.
-If the code returns after replacement, recheck the relay socket and power feed before buying more parts.

Background

What this code means

P0418 is a generic OBD-II code for a secondary air pump relay A circuit malfunction.

That means the ECU is not seeing the relay operate the way it expects when the secondary air system should be active during cold start.

Diagnosis

Common causes

Most common

Failed relay

The relay may no longer switch reliably when commanded.

Common

Blown fuse or feed issue

The relay may not be getting the supply it needs.

Common

Connector or socket damage

Heat or corrosion can keep the relay from making contact.

Possible

Harness fault

A wiring problem can make the relay circuit behave erratically.

Avoid these mistakes

What not to do

xDo not replace the sensor or valve first if there is obvious wiring, connector, or vacuum damage.
xDo not ignore drivability changes just because the code sounds like an emissions fault.

Parts

Parts that may need replacing

PartTypical costNotes

Secondary air pump relay$15-$60Often the first inexpensive part to consider.

Fuse or relay socket repair$10-$80Relevant if the supply side or socket is damaged.

Connector or harness repair$15-$120Useful if the circuit is corroded or broken.

Related OBD codes

P0410

P0410 usually means the secondary air injection system is not working properly.

P0411

P0411 usually means the secondary air injection flow is incorrect.

P0412

P0412 usually means the secondary air injection control circuit has a malfunction.

P0413

P0413 usually means the secondary air injection valve circuit is malfunctioning.

P0414

P0414 usually means the secondary air injection switch valve A is shorted or malfunctioning.

P0415

P0415 usually means the secondary air injection switch valve B has a circuit malfunction.

P0416

P0416 usually means the secondary air system switch valve B is malfunctioning.

P0417

P0417 usually means the secondary air system switch valve B circuit is shorted.

Source notes

Generic OBD-II (SAE J1979 / ISO 15031-5). P0418 was expanded around common secondary-air pump relay faults, including relay failure, fuse problems, and socket or harness damage.

This guide is written as a generic multi-make reference, so bulletin history, sensor locations, and repair order can still change by manufacturer and engine family.

This is generic OBD-II guidance and should not override vehicle-specific service information. Exact diagnosis and repair steps vary by make, engine family, and model year.

Last reviewed: 2026-04-10

Reference: Open reference

P0418 - P0418 Usually Means the Secondary Air Pump Relay a Circuit Has a Malfunction