P0412
Secondary Air Injection System Switching Valve A Circuit MalfunctionP0412 is a generic OBD-II powertrain diagnostic trouble code: Secondary Air Injection System Switching Valve A Circuit Malfunction. It is logged by the engine control unit when the egr monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P0412 means
P0412 is stored when the PCM detects a fault in the electrical circuit controlling the Secondary Air Injection System (SAIS) switching valve "A". This valve directs fresh air from the air pump into the exhaust ports during a cold start, helping the catalytic converter reach operating temperature faster and reducing hydrocarbon and CO emissions. The code specifically targets the switching valve circuit — not the air pump itself or downstream flow faults, which have their own codes (P0410, P0411).
The switching valve is energised by the PCM through a relay or driver circuit. If the PCM commands the valve on but sees no confirming voltage change, or detects an open or high-resistance condition in the coil, it logs P0412. Common vehicles affected include Toyota, Subaru, BMW, and Mercedes-Benz models fitted with active SAIS. On most engines the system only runs for the first 60–120 seconds after a cold start, so the fault may only be apparent on initial start-up.
Because this is an emissions-related circuit fault, the MIL illuminates and the vehicle will typically fail an emissions test. Driveability impact is minimal under normal driving conditions, but the catalytic converter may take longer to reach light-off temperature, increasing catalyst wear over time.
Common causes
Most-frequently reported root causes when P0412 is logged.
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1
Failed or shorted switching valve solenoid coil (most common).
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2
Open circuit or broken wire in the harness between the PCM/relay and the switching valve connector.
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3
Corroded or loose connector at the switching valve.
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4
Faulty AIR pump relay not supplying power to the valve circuit.
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5
Damaged vacuum hose to the switching valve preventing it from responding to control signals (on vacuum-operated designs).
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6
PCM driver circuit fault (rare, typically only after ruling out all external wiring).
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7
Moisture intrusion into the connector causing intermittent high resistance.
Symptoms drivers notice
How to diagnose P0412
A typical diagnostic flow when this code is present.
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1
Connect a scan tool and confirm P0412 is present; note any companion codes (P0410 pump fault, P0411 flow fault) to isolate electrical vs. mechanical/flow problems.
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2
With the engine cold, command the AIR pump solenoid ON via the scan tool's bi-directional controls (KOEO) and listen for the pump and valve to activate.
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3
If the valve does not activate, unplug the switching valve connector and check for supply voltage at the harness side when the PCM commands it on.
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4
Measure resistance across the switching valve solenoid terminals with a multimeter; compare to the manufacturer spec (typically 20–60 ohms) — an open reading confirms a failed coil.
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5
Inspect the wiring harness from the PCM/relay to the valve connector for chafing, corrosion, or broken wires; perform a wiggle test while monitoring live data.
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6
Check the AIR pump relay for correct operation by swapping with an identical relay or testing relay coil resistance.
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7
If wiring and valve test good, check PCM output voltage with a lab scope; replace or reprogram the PCM only after all external causes are eliminated.
Related powertrain codes
- P0400 — Exhaust Gas Recirculation Flow Malfunction
- P0401 — Exhaust Gas Recirculation Flow Insufficient Detected
- P0402 — Exhaust Gas Recirculation Flow Excessive Detected
- P0403 — Exhaust Gas Recirculation Circuit Malfunction
- P0404 — Exhaust Gas Recirculation Circuit Range/Performance
- P0405 — Exhaust Gas Recirculation Sensor A Circuit Low
Frequently asked questions
Can I drive with a P0412 code?
Yes, the vehicle remains driveable. The fault only affects cold-start emissions for the first couple of minutes after start-up, so there is no immediate safety or performance risk. However, you will fail an emissions test, and prolonged operation without the SAIS can accelerate cold-start catalyst wear.
Is P0412 the same as P0410 or P0411?
No. P0410 means the PCM detected insufficient airflow from the SAIS (a flow or pump fault), P0411 indicates incorrect flow (e.g., a stuck valve), and P0412 specifically flags an electrical circuit fault at the switching valve "A". Always distinguish between circuit codes and flow codes before replacing components.
Which vehicles are most commonly affected?
P0412 is particularly common on Toyota Tacoma, 4Runner, and Tundra trucks (V6/V8), Subaru boxer engines, BMW inline-six and V8 models (E39/E46/E60 era), and various Mercedes-Benz petrol engines. All use an active AIR pump with a solenoid-controlled switching valve.
How do I confirm the switching valve coil is faulty without a scan tool?
Unplug the switching valve connector and measure resistance across the two solenoid terminals with a multimeter. A healthy coil typically reads 20–60 ohms depending on the manufacturer. An OL (open loop) or near-zero reading (shorted coil) confirms the valve needs replacement.
Disabling P0412 in software
RaceTune can permanently disable P0412 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
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