P0412
Secondary Air Injection System Switching Valve A Circuit
When a vehicle powertrain module registers the fault code P0412, it points directly to an internal system malfunction identified as "Secondary Air Injection System Switching Valve A Circuit". Operating your engine under this condition may degrade long-term fuel maps.
Driver's Summary
P0412 is triggered when the PCM detects an abnormal condition associated with secondary air injection system switching valve a circuit. The most common signs are check engine light, failed cold-start emissions test. Low severity — the car drives normally, but the fault should be diagnosed and resolved within the next few weeks.
Symptoms
Check engine light, failed cold-start emissions test
Common Causes
- Failed secondary air injection switching valve
- Open or shorted wiring to the valve
- Blown fuse for the AIR system
- Corrosion in the valve connector
How to Fix
- 1 Test and replace air injection switching valve
- 2 Repair wiring harness
- 3 Check and replace related fuses
- 4 Clean connector contacts
Technical Explanation
P0412 is stored after the control module confirms the fault over multiple ignition cycles, ruling out transient electrical noise as the cause. EGR flow is verified by monitoring changes in MAP sensor readings before and after valve actuation; correct EGR flow produces a predictable pressure drop in the intake manifold that the ECM can measure with precision. After two failed drive cycles, the code transitions from a pending to a confirmed DTC, and the PCM activates the MIL. Clearing the code without repairing the fault will result in re-illumination within one to two complete drive cycles.
Is It Safe to Drive?
Code P0412 has minimal impact on immediate driving safety. However, the underlying failed secondary air injection switching valve issue will cause this vehicle to fail an emissions inspection and may gradually affect fuel economy if left unrepaired.
Mechanic's Pro Tip
For P0412, test the solenoid's coil resistance with a multimeter before ordering parts — most solenoids should read between 14 and 40 ohms; an open (infinite resistance) or short (near zero) confirms it's failed electrically. Also verify the PCM is commanding the solenoid by backprobing the connector with a test light during the relevant operating condition — if there's no command signal, the fault is in the PCM or wiring, not the solenoid itself.
Switching valve: $80 - $250