P0412 Code: Secondary Air Injection Switching Valve A Circuit
The ECU found an open or short in the circuit of the valve that routes air from the pump into the exhaust.
At a glance
Severity: Low
- Meaning
- Secondary Air Injection Switching Valve A Circuit
- System
- Emission Controls · Powertrain
- Safe to drive?
- Yes, short term
- Typical repair cost
- $40–$500
- DIY difficulty
- Easy
Besides the pump, a secondary air system needs a valve that opens the path to the exhaust only while the pump runs and keeps hot exhaust out the rest of the time. On many engines the ECU controls that with an electric switching valve: either a small solenoid that sends engine vacuum to a check valve, or an electrically operated shut-off valve on the air line itself. P0412 means the ECU detected an electrical problem in the circuit of switching valve A, such as an open coil, a broken wire or a short. It says nothing about the pump or the air passages, so the diagnosis is a straightforward electrical one.
Can I keep driving? Safe to drive. The secondary air system is only active for a short time after cold starts, so the engine runs normally; just plan the repair before your next emissions test.
How to read P0412
- P Powertrain
- 0 Generic (SAE)
- 4 Auxiliary emission controls
- 12 Specific fault
Symptoms
- Check engine light on
- No noticeable change in driving
- A companion P0410 or P0411 because air can't get through without the valve opening
- Corroded or cracked connector at a small solenoid near the air pump or intake
- Secondary air monitor incomplete
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Solenoid coil open or shorted
- Corroded or water-filled connector at the switching valve
- Broken or chafed wire between the ECU and the valve
- Missing power feed: blown fuse or failed feed from the pump relay circuit
- Incorrect or aftermarket solenoid with the wrong coil resistance
- ECU output driver fault
Diagnosis step by step
Locate switching valve A
Use a repair manual or parts diagram to find the valve; it's usually a small solenoid with an electrical connector and two or three hoses near the air pump, the intake manifold or on the air line to the check valve. On some trucks the air shut-off valve is electrically operated and mounted on the pump outlet.
Tools: Flashlight
Inspect the connector and hoses
Unplug the connector and look for corrosion, water and bent pins, then check the vacuum hoses on the valve for cracks. A disconnected vacuum hose won't set P0412, but it will cause a P0411 afterwards, so fix both while you're there.
Tools: Flashlight, Screwdriver
Measure coil resistance
Measure across the valve's two terminals and compare with the spec, which is typically a few tens of ohms. An open reading (OL) or near zero ohms condemns the valve.
Tools: Multimeter
Bench-test the valve
Connect a hand vacuum pump to the valve's supply port and power the coil briefly with fused jumper leads from the battery. You should hear a click and the vacuum path should switch; a valve that clicks but doesn't switch is stuck mechanically.
Tools: Vacuum gauge, Multimeter
Check power and ECU control
With the key on, check for battery voltage on the feed terminal. Then connect a test light across the connector and command the valve with a scan tool; the light should turn on with the command, proving the ECU and wiring are good.
Tools: Multimeter, OBD-II scanner
Clear the code and do a cold start
After the repair, clear the code and let the car sit until fully cold. A cold start with the pump and valve working should complete the secondary air monitor without P0412 or its companion codes returning.
Tools: OBD-II scanner
Where the parts are
- 1Upstream O2 sensor
- 2Catalytic converter
- 3Downstream O2 sensor
- 4Diesel particulate filter
- 5Turbocharger
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Clean or replace connector | Yes | $40–$150 |
| Replace secondary air switching solenoid | Yes | $80–$250 |
| Repair wiring | No | $100–$300 |
| Replace electrically operated air shut-off valve | No | $200–$500 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Notes by brand
Chevrolet
On GM trucks and SUVs with the V8 AIR system, the electrically operated shut-off valve sits on the air line near the pump and is exposed to condensate. P0412 on these vehicles is often a corroded valve or connector, and it frequently shows up together with P0410.
Emissions / smog test impact
Will fail
P0412 with the check engine light on fails OBD-based smog checks. The secondary air monitor needs a genuine cold start to run, so allow for that before a retest.
Frequently asked questions
Is P0412 the same as a bad air pump?
No. P0412 is about the electrical circuit of the valve that lets the pumped air into the exhaust. The pump can be perfectly fine; if the valve doesn't open, though, you'll often see P0410 or P0411 as well.
Can I test the switching valve at home?
Yes. A multimeter for the coil resistance, a hand vacuum pump and two fused jumper leads to the battery are enough to see whether the valve clicks and switches.
What does 'A' mean in P0412?
It identifies the first switching valve in the manufacturer's system. Most vehicles have only one; V engines with separate air paths for each bank may also have a valve B, which has its own codes.
Sources
- SAE J2012 – Diagnostic Trouble Code Definitions
- ISO 15031-6 – Road vehicles, diagnostic trouble code definitions (EOBD)
- Manufacturer public service information (cross-checked)
- Methodology: How We Build Code Pages · Data Sources We Use · Editorial Policy