P0415 is an OBD-II trouble code that points to an electrical problem in your vehicle’s secondary air injection system, specifically the “B” circuit of the switching valve or solenoid. While this code usually won’t leave you stranded, it does affect how cleanly your engine runs during cold starts and can cause your check engine light to stay on. Understanding what P0415 means, how it shows up, and how to track it down will help you decide whether it’s a simple DIY repair or something you should leave to a professional.
What Does P0415 Mean?
P0415 stands for “Secondary Air Injection System Switching Valve B Circuit Malfunction.” In plain language, your engine computer (ECU) has detected an electrical fault in the control circuit for one of the secondary air injection valves or solenoids, labeled “B.” This system pumps fresh air into the exhaust during cold starts to help burn off extra fuel and reduce emissions.
The ECU monitors voltage and current on this circuit. If it sees an open circuit, short to power, short to ground, or a signal that doesn’t match what it commanded, it stores P0415 and usually turns on the check engine light. The “B” designation simply identifies which valve or circuit is affected when there are multiple valves in the system.
Quick Reference
- Code: P0415 – Secondary Air Injection Switching Valve B Circuit Malfunction
- Severity: Low to moderate (mainly emissions and drivability on cold start)
- Common Causes: Bad air switching solenoid, wiring damage, corroded connector, blown fuse, relay issues
- Typical Symptoms: Check engine light, rough cold start, increased emissions, possible failed smog test
- System Affected: Secondary Air Injection (SAI) / Air pump system
Real-World Example / Field Notes
In the shop, P0415 often shows up on vehicles that see a lot of winter driving or road salt. One common scenario: a customer complains that the check engine light came on after a cold snap, but the car “drives fine.” On inspection, the secondary air injection valve harness is often brittle, with green corrosion inside the connector and sometimes broken wires near the plug. Another pattern is a failed air switching solenoid full of moisture. The ECU tries to command the valve on, doesn’t see the expected electrical response, and sets P0415. Fixing the wiring or replacing the solenoid usually clears the code for good.
Symptoms of P0415
- Check engine light on: The most obvious sign is the MIL (Malfunction Indicator Lamp) illuminated on the dash.
- Rough cold start: You may notice a slightly rough idle or stumble right after starting the engine, especially in cold weather.
- Increased exhaust smell: A stronger fuel or exhaust odor on cold start, since extra emissions aren’t being burned off as designed.
- Failed emissions test: The car may fail a smog or inspection test due to stored codes or elevated cold-start emissions.
- Air pump noise changes: On some vehicles, you might hear the secondary air pump run oddly or not at all during the first minute after start-up.
- Other SAI-related codes: You may see P0410, P0412, P0413, or similar codes stored along with P0415.
- Intermittent drivability issues: Rarely, you may feel slight hesitation on initial acceleration when the engine is still cold.
Common Causes of P0415
Most Common Causes
- Failed switching valve / solenoid “B”: The internal coil can open or short, causing incorrect resistance and triggering the code.
- Damaged wiring harness: Broken, rubbed-through, or corroded wires to the secondary air valve are extremely common, especially near the valve or pump.
- Corroded or loose connector: Moisture and road salt can get into the electrical connector, causing poor contact and high resistance.
- Blown fuse or bad relay: A fuse or relay feeding the SAI valve or pump can fail, cutting power to the circuit.
- Poor ground connection: A weak or rusty ground point can cause voltage drops and confuse the ECU’s monitoring of the circuit.
Less Common Causes
- Water intrusion in harness: Water wicking through the loom can cause intermittent shorts in the SAI circuit.
- Defective secondary air pump: A failing pump can overload the circuit or cause related codes, though it’s more often tied to flow codes than circuit codes.
- ECU driver failure: Rarely, the engine control unit’s internal transistor that controls the valve fails, causing a permanent circuit fault.
- Incorrect aftermarket wiring or modifications: Remote starters, alarms, or poorly installed accessories can tap into the wrong circuit and create issues.
- Previous collision or repair damage: Body or engine work may pinch or misroute the harness feeding the SAI components.
Diagnosis: Step-by-Step Guide
For diagnosing P0415, you’ll want a basic scan tool (preferably one that can read live data and Mode $06), a digital multimeter, and simple hand tools. A wiring diagram and service information for your specific vehicle are extremely helpful. If you’re comfortable checking voltage, resistance, and grounds, this is a reasonable DIY project. If not, a professional technician can run these checks quickly.
- Confirm the code and check for others. Connect your scan tool, read stored and pending codes, and note any related SAI codes (P0410–P0419 range). Clear the codes and see if P0415 returns quickly or only after a cold start.
- Perform a visual inspection. Locate the secondary air injection switching valve “B” and its connector. Look for broken clips, cracked insulation, rubbed-through wires, or signs of corrosion and moisture.
- Check fuses and relays. Using the owner’s manual or wiring diagram, identify the SAI system fuses and relays. Test them with a test light or meter and replace any that are blown or suspect.
- Test the valve/solenoid coil. With the connector unplugged and ignition off, measure resistance across the valve’s two terminals using a multimeter. Compare to spec (often between 10–40 ohms, but check your manual). Infinite resistance indicates an open coil; near zero may indicate a short.
- Verify power and ground at the connector. With the ignition on and using a wiring diagram, back-probe the connector. Check for proper battery voltage on the power feed and a good ground when the ECU commands the valve on (you may need a scan tool’s “actuator test” function).
- Check for shorts to ground or power. If the fuse keeps blowing or readings are off, disconnect both ends of the circuit and check continuity to ground and to power. Any unexpected continuity indicates a short that needs to be traced and repaired.
- Use live data or Mode $06 if available. Some scan tools let you monitor SAI command status and test results. Watch when the ECU commands the valve on and see if the circuit responds as expected.
- Wiggle test the harness. While monitoring the circuit with a meter or scan tool, gently move the harness and connector. If the readings jump or the code sets, you’ve likely found a broken wire or poor connection.
- Suspect ECU only after all else passes. If the valve, wiring, fuses, and relays all test good but the ECU never properly commands the circuit, an internal ECU fault is possible and should be confirmed by a professional.
Pro Tip: When replacing a failed SAI valve or repairing wiring, always clean and protect the connector with dielectric grease and secure the harness away from hot exhaust components. This helps prevent repeat failures of P0415 down the road.
Possible Fixes & Repair Costs
Fixing P0415 usually involves restoring proper electrical control to the secondary air switching valve “B.” Common repairs include replacing the faulty valve/solenoid, repairing or replacing damaged wiring and connectors, cleaning corrosion, or replacing a blown fuse or bad relay. In rare cases, the ECU may need replacement and programming.
- Replace switching valve / solenoid “B”: Parts typically $60–$200; labor $80–$200 depending on access.
- Repair wiring or connector: Shop repairs usually $100–$250, depending on how deep the harness damage goes.
- Replace fuse or relay: Parts $5–$40; often minimal labor if easily accessible.
- Secondary air pump replacement (if also failed): Parts $150–$500; labor $150–$400.
- ECU repair or replacement (rare): $400–$1,200+ including programming.
Overall, most P0415 repairs fall in the $150–$500 range at a typical shop. Costs vary with vehicle make, how buried the components are, local labor rates, and whether additional SAI parts are failing at the same time.
Can I Still Drive With P0415?
In most cases, you can still drive with P0415 without immediate risk of engine damage. The secondary air injection system mainly operates during cold starts to reduce emissions, so it doesn’t affect basic engine operation once the engine is warm. However, you may experience rougher cold starts, increased exhaust smell, and a persistent check engine light.
The bigger concern is emissions compliance. With P0415 active, your vehicle may not pass an inspection or smog test. Also, driving long-term with any active code makes it easy to miss new problems since the check engine light is already on. It’s best to diagnose and repair P0415 as soon as practical.
What Happens If You Ignore P0415?
If you ignore P0415, you’re mainly risking higher cold-start emissions, potential catalytic converter stress from richer mixtures, and guaranteed inspection or smog test problems in many regions. Over time, moisture and corrosion in the SAI wiring or connectors can spread, turning a simple repair into a more expensive harness or component replacement.
Related Codes
- P0474 – Exhaust Pressure Sensor Intermittent
- P0473 – Exhaust Pressure Sensor High
- P0472 – Exhaust Pressure Sensor Low
- P0471 – Exhaust Pressure Sensor Range/Performance
- P0470 – Exhaust Pressure Sensor
- P0469 – EVAP Purge Flow Sensor Circuit Intermittent
- P0468 – EVAP Purge Flow Sensor Circuit High
- P0467 – EVAP Purge Flow Sensor Circuit Low
- P0466 – EVAP Purge Flow Sensor Circuit Range/Performance
- P0465 – EVAP Purge Flow Sensor Circuit
Key Takeaways
- P0415 indicates an electrical problem in the secondary air injection switching valve “B” circuit, not necessarily a mechanical engine issue.
- Common culprits are a failed solenoid, damaged wiring, corroded connectors, or a blown fuse or relay.
- Symptoms are usually mild and focused around cold starts and emissions, but the check engine light will stay on.
- Diagnosis involves checking resistance, power, ground, and continuity in the SAI circuit with a scan tool and multimeter.
- Most repairs cost between $150 and $500, depending on parts, labor, and how much wiring work is needed.
- Driving is usually safe in the short term, but you risk failing inspections and masking other potential issues.
Vehicles Commonly Affected by P0415
P0415 shows up across many makes that use electric secondary air injection systems. It’s especially common on:
- Volkswagen and Audi: Many 1.8T, 2.0T, and V6 models with electric air pumps and multiple switching valves.
- GM (Chevrolet, GMC, Buick, Cadillac): Trucks and SUVs with V6 and V8 engines that use SAI for emissions compliance.
- Toyota and Lexus: Some V6 and V8 engines with complex SAI systems and multiple valves and pressure sensors.
- BMW and Mercedes-Benz: Various inline-6 and V8 models, where heat and tight engine bays can be hard on wiring.
- Ford and Mazda: Select models with SAI systems, especially in regions with strict emissions requirements.
Even if your car isn’t on this list, any OBD-II vehicle with a secondary air injection system and multiple valves can potentially set P0415.
FAQ
Can I clear P0415 and keep driving without fixing it?
You can clear the code, but it will almost always come back if the underlying electrical problem is still there. Clearing it doesn’t fix the issue, and repeated cold starts with a malfunctioning SAI system can eventually stress other components and cause inspection failures.
Is P0415 an expensive repair?
Usually, P0415 is not among the most expensive repairs. Many fixes fall in the $150–$500 range, depending on whether you need a new solenoid, wiring repair, or just a fuse/relay. Costs climb if the harness is badly damaged or if the air pump or ECU also needs replacement.
Can a bad secondary air pump cause P0415?
Yes, a failing air pump can indirectly contribute to P0415, especially if it overloads the circuit or causes related electrical issues. However, P0415 specifically points to a circuit problem with the switching valve “B,” so you should test the valve, wiring, and power/ground first before condemning the pump.
How do I know which valve is “B” on my car?
The “B” designation is manufacturer-specific. On some vehicles it’s the second valve in the system or the one serving a particular bank of cylinders. You’ll need to consult a wiring diagram or service manual for your exact year, make, and model to identify which physical valve is labeled “B.”
Can a bad ground cause P0415?
Absolutely. A weak or corroded ground can cause voltage drops and make the ECU think there’s an open or short in the circuit. Always check ground points and clean or tighten them as part of your P0415 diagnosis, especially on older or high-mileage vehicles.