P0412
AIR System Switching Valve A Circuit
Secondary air injection (emissions)
Generic OBD-II
Medium
What it means
P0412 means the ECM has detected an electrical fault in the secondary air injection switching valve A circuit. This valve routes fresh air into the exhaust at cold start to help the catalytic converter warm up and cut emissions. The engine drives normally, but the fault will trigger the check-engine light and cause an emissions-test failure.
Medium
Can I keep driving? The engine drives normally — the main consequences are a check-engine light and a failed emissions test.
Common symptoms
What you'll notice
- Check-engine light on
- Failed emissions test
- Usually no change in how the engine drives
- Possible brief rough idle only during cold start when secondary air runs
Common causes
Most likely first
- Faulty secondary air injection switching valve A (solenoid)Likely
- Open or shorted wiring in the switching valve control circuitCommon
- Poor or corroded connector at the valveCommon
- Faulty relay or fuse feeding the secondary air systemLess often
- Faulty ECM (least likely)Less often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and confirm the fault is the secondary air switching valve A circuit.
- Inspect the valve's connector and control wiring for damage or corrosion.
- Check power, ground, and the ECM control signal at the valve.
- Test the switching valve solenoid's resistance against specification.
- Replace the valve or repair the wiring as indicated. Clear and re-test.
FAQ
Quick answers
Is it safe to drive with P0412?+
Yes — the secondary air system only affects cold-start emissions, so the engine drives normally. You'll need it fixed to pass an emissions test, though.
Can I just clear P0412?+
It will return until the valve or its circuit is repaired, and the emissions monitor won't pass with the fault present.
Related codes
Often seen with P0412
Read & clear P0412 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX