P0412: AIR System Switching Valve A Circuit
A generic powertrain (engine and transmission) trouble code, same meaning on every brand.
Yes.
Symptoms
- Check engine light
- Secondary air pump not running when it should
- Emissions failure
Likely causes, most common first
- Switching valve solenoid open or shorted
- Wiring fault
- Blown fuse
- Failed relay
Read P0412 yourself before paying for diagnosis
A basic Bluetooth OBD-II scanner ($20-40) plugs into the port under the dashboard and shows this code with live sensor data on your phone - useful both for confirming the fix and for talking to a shop from an informed position.
What is going on and how it gets diagnosed
P0412 is an electrical fault in the valve that routes secondary air into the exhaust. Unlike the flow codes around it, this one is diagnosed with a meter, not by listening: the solenoid either has the right resistance and supply voltage, or it does not.
These valves switch hot, moisture-laden air, so the solenoid and its connector age faster than their sheltered location suggests. A straightforward bench test - apply power and listen for the click - separates a dead valve from a wiring problem in under a minute once the connector is in hand.
Repair options and cost
Typical US independent-shop ranges, parts and labor. Dealers run higher; regional labor rates vary.
Owner reports mentioning P0412
“I have an 2006 lexus gx470 and these lights came on: ABS, vsc trac, vsc off, skid, and check engine. The vehicle started making a humming noise at start up and now drives in stalled mode. Had codes check and it turns out I have the dreaded secondary air injection system (emissions) defect p0412, p0418 ,p1440/p1443, p1441/p1444, p2440, p2445, p1442/p1145 , which is a recurring problem. Replacement is a nightmare for self repair or a $2000+ repair.”2006 Lexus GX470 · Jun 2018 · 125,000 mi
“2012 tacoma with 24k miles. Check engine light and trc light came on with truck in limp mode when I started it to go to work. Codes p0412 p2433 p2438 p2442. Toyota wont cover this and its a defect in many many 2012 tacomas.”2012 Toyota Tacoma · May 2017 · 24,000 mi
Cars that report P0412 most often
Based on mentions of this code in NHTSA owner complaints.
Frequently asked questions
Can I drive with P0412?
Yes.
How much does it cost to fix P0412?
Typical US repair costs range from $20 for the simplest fix (fuse or relay) to $400 in the worst case. The right number depends on which cause your car has - see the causes list.
Related codes
The codes closest to P0412. They often appear together, and telling them apart is usually what narrows the diagnosis.
Definition per SAE J2012 standard nomenclature. Symptoms, causes and costs are editorial guidance - always confirm with a diagnosis of your specific vehicle.