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DTC codes / P04xx · Auxiliary emission controls / P0415

P0415Secondary Air Injection System Switching Valve 'B' Circuit

P0415 indicates that the powertrain control module (PCM) has detected an electrical fault in the control circuit for the secondary air injection (AIR) system's switching valve 'B'. The PCM monitors the valve's control wire for expected voltage changes when commanding the valve on and off, and it sets this code when the circuit does not respond as designed, which can prevent the AIR system from reducing cold-start emissions.

SystemPowertrain
Code typeGeneric (all makes)
SeverityLow
Fix difficultyIntermediate
AreaAuxiliary emission controls

Symptoms you may notice

  • Illumination of the check engine light, often with no other noticeable symptoms
  • A slight hesitation or rough idle during the first minute after a cold start
  • A brief, faint hissing or rushing air sound from the engine bay that may be absent or constant
  • Failed emissions inspection due to the check engine light being on
  • In rare cases, a noticeable exhaust odor during warm-up if the AIR system is not functioning

Common causes, most likely first

  1. Open or shorted wiring in the switching valve 'B' control circuit, including chafed insulation or broken conductors
  2. Failed secondary air injection switching valve 'B' solenoid or actuator
  3. Corroded, loose, or damaged electrical connector at the switching valve or PCM
  4. Blown fuse or faulty relay that supplies power to the switching valve circuit
  5. Internal PCM driver failure affecting the control circuit (less common)
  6. Water intrusion or contamination in the valve connector causing intermittent faults

How to diagnose and fix it

  1. Scan all modules and record freeze-frame data to confirm P0415 is the primary fault and not a secondary code
  2. Visually inspect the switching valve 'B' connector, wiring harness, and vacuum lines for damage, corrosion, or disconnection
  3. Check the fuse and relay that supply power to the secondary air injection system and replace if faulty
  4. Use a digital multimeter to measure resistance and voltage on the control circuit at the valve and at the PCM, comparing to manufacturer specifications
  5. Command the switching valve on and off with a scan tool while monitoring circuit voltage or listening for the valve to click, to verify PCM control and valve operation
  6. If the circuit tests good but the valve does not respond, replace the switching valve 'B' and clear the code
  7. If the circuit is faulty, repair the wiring or connector, then clear codes and verify the repair with a road test that includes a cold start

Don't overlook the simple electrical checks

  • A loose or corroded ground connection for the secondary air injection system can mimic a failed switching valve and set P0415 without any faulty component.
  • The PCM may set P0415 if the switching valve 'B' circuit is mechanically stuck or restricted, not just for electrical opens or shorts, so always verify valve operation with a scan tool command.
  • Aftermarket alarm or remote start wiring tapped into the harness near the AIR system can introduce resistance or intermittent shorts that trigger this code.
  • P0415 is often stored alongside P0410 or P0411, and diagnosing those codes first can reveal a shared root cause such as a failed air pump or blocked passage.
  • Clearing the code without repairing the underlying circuit will usually result in the code returning after one or two cold-start drive cycles.

Can I keep driving with P0415?

The vehicle remains safe to drive with P0415 because the fault only affects cold-start emissions and does not impair engine performance or safety. Avoid long-term driving with the check engine light on, as you may not notice a more serious fault that could develop, and schedule diagnosis soon to ensure the AIR system operates correctly for emissions compliance.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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