What causes fault code P0412?

• Most likely: Faulty SAI switching solenoid valve (internal electrical failure) • Likely: Corroded or damaged connector at the valve • Possible: Wiring harness open circuit or short to ground/power • Rare: Faulty SAI relay (if sharing the same power feed) • Rare: Internal Engine Control Module (ECM) fault

How do you fix fault code P0412?

Visual Inspection: Check the connector and wiring harness for corrosion, backing out pins, or signs of heat damage. Fuse Check: Verify the integrity of fuses related to the Secondary Air Injection system. Resistance Test: Disconnect the solenoid and measure resistance across the terminals. Typical values are 20–50 Ohms. Infinite resistance indicates an open coil. Voltage Test: Check for 12V power supply at the connector with the key on (or during actuation test). Bidirectional Test: Use a scan tool to command the solenoid 'ON' and 'OFF' while listening for an audible click. Replacement: If the solenoid fails resistance or functional tests, replace the SAI switching valve.

Powertrain (Engine & Gearbox)Standard EOBD

P0412 - Secondary Air Injection System Switching Valve 'A' Circuit Malfunction

Q: What are the symptoms of fault code P0412?

• Check Engine Light (MIL) illuminated • Engine may hesitate slightly during cold start warm-up • Increased emission levels (will fail emissions test if code is active) • Abnormal noise (hissing or humming) from the engine bay during cold starts

Last updated:1 February 2026

Related:Switching Valve, AIR Pump, Secondary Air Injection Relay, Engine Control Unit (ECU/ECM), Kablage och kontaktstycken

System

Powertrain (Engine & Gearbox)

Related Fault Codes

P0400

Exhaust Gas Recirculation Flow Malfunction

P0401

Exhaust Gas Recirculation (EGR) Flow Insufficient Detected

P0402

Exhaust Gas Recirculation Flow Excessive Detected

P0403

Exhaust Gas Recirculation (EGR) Control Circuit

Technical Description

Diagnostic Trouble Code (DTC) P0412 points to an electrical malfunction in the circuit of the Secondary Air Injection (SAI) switching valve 'A'. The SAI system reduces emissions during cold starts by injecting fresh air into the exhaust stream, promoting the oxidation of HC and CO and heating up the catalytic converter faster. The Engine Control Module (ECM) monitors the continuity and voltage of the solenoid circuit. If the ECM detects a deviation from the expected voltage (open circuit, short to ground, or short to power) when the solenoid is commanded, P0412 is stored. This code specifically relates to the electrical integrity of the control circuit rather than pneumatic flow issues.

Possible Causes

Faulty SAI switching solenoid valve (internal electrical failure)

Corroded or damaged connector at the valve

Wiring harness open circuit or short to ground/power

Faulty SAI relay (if sharing the same power feed)

Internal Engine Control Module (ECM) fault

Symptoms

Check Engine Light (MIL) illuminated

Engine may hesitate slightly during cold start warm-up

Increased emission levels (will fail emissions test if code is active)

Abnormal noise (hissing or humming) from the engine bay during cold starts

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P0412 - Secondary Air Injection System Switching Valve 'A' Circuit Malfunction

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P0412 - Secondary Air Injection System Switching Valve 'A' Circuit Malfunction

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