P0412 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 air system wiring and valves
2
Free - no tools
Inspect the relay, connector, and harness for heat damage, corrosion, or looseness
3
Basic tool needed
Check whether the code appeared after wet weather or a recent repair near the pump or valve
4
Basic tool needed
If scan data is available, compare commanded air injection with actual response
5
Basic tool needed
If the pump never comes on, start with the electrical side before replacing the pump or valve

If the code returns

-If the relay is not being energized properly, follow the command path back toward the ECU.
-If the pump works on direct power but not in normal operation, the control circuit is more likely.
-If the code returns after a repair, recheck the connector and routing before buying another part.

Background

What this code means

P0412 is a generic OBD-II code for a secondary air injection control circuit malfunction.

That usually means the ECU cannot operate the air system the way it expects, even if the pump or valve still works some of the time.

Diagnosis

Common causes

Most common

Control relay fault

The relay may not be passing or receiving the proper command.

Common

Connector or wiring damage

Heat and moisture can interrupt the control circuit.

Common

Valve or solenoid issue

The command path may be fine but the component is not responding.

Possible

ECU command issue

The control request may not be getting through correctly.

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

Secondary air pump or valve$150-$600Relevant if the component itself is not responding.

Connector or wiring repair$15-$120Useful if the circuit is damaged or corroded.

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.

P0413

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

Source notes

Generic OBD-II (SAE J1979 / ISO 15031-5). P0412 was expanded around common secondary-air control-circuit faults, especially relay issues, wiring damage, and valve command problems.

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

P0412 - P0412 Usually Means the Secondary Air Injection Control Circuit Has a Malfunction