P0412

Code

Generic P — Powertrain

AIR System Switching Valve A Circuit

Brand: Generic

Type: P — Powertrain

Views: UK: 37 EN: 67 RU: 51

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Page language: EN

Causes

Open or short in the switching valve A wiring or connector
Failed AIR switching valve (solenoid or actuator)
Blown fuse or faulty relay for AIR system circuit
Corroded/loose connector or poor ground
Faulty ECM drive output (rare)

Symptoms

Malfunction Indicator Lamp (MIL) / Check Engine Light illuminated
Failed or reduced secondary air injection during cold start (emissions impact)
Possible rough cold idle or unusual exhaust smell on some vehicles
Possible stored emission-related trouble codes

What to check

Retrieve freeze-frame and live data with a scan tool; confirm P0412 and any related codes
Visual inspection of AIR switching valve A, harness, and connector for damage, corrosion, or loose pins
Check fuse(s) and relay(s) for the AIR system power feed
Measure resistance of the switching valve coil at the connector (with harness disconnected)
Backprobe connector while commanding valve ON/OFF to observe control voltage and ground
Wiggle test harness while monitoring for intermittent faults

Signal parameters

Control supply: typically battery voltage (approx. 12 V) to the valve power terminal when fused/powered
ECM drive: ground-switching or low-side drive; commanded ON should show ~0 V on switched side (or a pull to ground), OFF shows ~12 V (or open circuit) depending on design
Typical solenoid coil resistance: commonly in the range of ~5–40 ohms (varies by application) — check vehicle-specific spec
No continuity (open) indicates broken coil or wiring; short-to-ground or short-to-VB will show abnormal readings

Diagnostic algorithm

Verify the code with a scan tool and note freeze-frame data; check for related codes (P0410–P0415 series).
Perform a visual inspection of the AIR switching valve A, connectors, harness, nearby components and mounting (look for heat damage, rubbing, corrosion).
Check AIR system fuses and relays; replace if blown or faulty and retest.
Unplug the valve connector and measure coil resistance across the valve terminals. Compare to vehicle-specific spec. If open or outside range, replace valve.
With harness connected, backprobe power and control pins. Command the valve ON with a scan tool and observe voltages: verify battery feed and ECM switching/ground signal. If no command signal, check ECM output and wiring continuity.
Check continuity from the valve connector to the ECM pin for opens/shorts. Repair any damaged wires or poor grounds.
If wiring and connector are good but valve does not actuate when 12 V is applied directly (bench test), replace the valve. If valve works with direct 12 V but not when commanded, suspect wiring or ECM output driver.
After repairs, clear codes and perform a drive cycle/functional test to confirm the fault does not return.
If intermittent or difficult problems persist, perform wiggle tests, inspect harness routing for intermittent shorts, and consider ECU testing only after all wiring and components are proven good.

Likely causes

Damaged wiring harness to AIR switching valve A (chafing, rodent damage, broken wires)
Water intrusion/corrosion at valve connector
Stuck or mechanically jammed valve
Defective AIR switching valve coil (out-of-spec resistance or not energizing)
Blown fuse or defective AIR system relay

Fault status

⚠️ Status

ECM detected abnormal electrical condition in AIR switching valve A circuit (open/short/high/low). MIL/Check Engine light set and trouble code stored.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours

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