P0416 is an OBD-II trouble code related to your vehicle’s Secondary Air Injection (SAI) system, specifically an electrical fault in switching valve “B”. While it doesn’t usually leave you stranded, it does mean your emissions system isn’t working the way the ECU expects. That can lead to a failed smog test, a check engine light that won’t go away, and in some cases rough running on cold starts. In this guide, you’ll learn what P0416 means, common causes, symptoms, and how you or your mechanic can accurately diagnose and repair it.
What Does P0416 Mean?
P0416 stands for “Secondary Air Injection System Switching Valve B Circuit Malfunction.” In plain language, your ECU has detected an electrical problem in the control circuit for the “B” air switching valve (also called an air diverter or combination valve) in the secondary air injection system.
The SAI system pumps fresh air into the exhaust during cold starts to help burn off extra fuel and reduce emissions. When the ECU commands valve B on or off, it expects to see a specific voltage or feedback. If the signal is out of range, shorted, or open, it sets code P0416 and turns on the check engine light.
Quick Reference
- Code: P0416
- System: Secondary Air Injection (SAI)
- Component: Switching Valve “B” control circuit
- Severity: Low to moderate (emissions-related)
- Typical fix: Electrical repair, valve replacement, or pump/relay repair
Real-World Example / Field Notes
In the shop, I most often see P0416 on higher-mileage vehicles that see a lot of short trips. One case was a mid-2000s sedan that kept failing its state inspection for an emissions readiness issue. The owner had already replaced the air pump based on a parts-store suggestion, but the code came right back. A quick check with a multimeter showed a corroded connector and a partially broken wire at the switching valve B. After repairing the wiring and clearing the code, the SAI monitor ran properly, the car passed inspection, and the owner avoided buying more unnecessary parts.
Symptoms of P0416
- Check engine light on: The most obvious sign is an illuminated MIL with stored code P0416.
- Failed emissions test: The SAI monitor may not complete, or the vehicle may fail due to a stored fault code.
- Rough cold start: In some vehicles, you may notice slightly rough idle or hesitation right after a cold start.
- Increased exhaust smell: You might notice a stronger fuel or exhaust odor on cold starts because extra hydrocarbons aren’t being burned off.
- Air pump not running: You may not hear the usual brief “vacuum cleaner” sound from the SAI pump after a cold start.
- Other SAI codes present: Codes like P0410, P0412–P0419 may appear along with P0416.
- Intermittent operation: The code may come and go if there is a loose connection or moisture in the circuit.
Common Causes of P0416
Most Common Causes
- Damaged or corroded wiring to the switching valve B (open circuit or short to ground/power).
- Faulty switching/combination valve B with internal electrical failure.
- Bad or loose electrical connector at the valve or SAI harness.
- Failed SAI relay or control module output affecting the valve B circuit.
- Water intrusion in the SAI wiring harness, especially in rust-belt or wet climates.
Less Common Causes
- Defective SAI air pump causing abnormal current draw that affects the valve circuit.
- Blown fuse for the SAI system or shared power circuit.
- Internal fault in the ECU/PCM driver for the switching valve B (rare).
- Previous incorrect wiring repairs or aftermarket modifications to the emissions system.
- Connector pin fitment issues (spread terminals) causing intermittent contact.
Diagnosis: Step-by-Step Guide
For diagnosing P0416, you’ll want a basic scan tool (preferably one that shows live data), a digital multimeter, a test light, and access to a wiring diagram for your specific vehicle. A smoke machine and bidirectional scan tool can make life easier, but they’re not mandatory for most DIYers.
- Confirm the code and check for companions. Use your scan tool to read all stored and pending codes. Note any other SAI-related codes (P0410–P0419) that may help point to a broader issue.
- Check freeze frame data. Look at when P0416 set (engine temperature, RPM, load). This helps you know if it occurs only on cold starts or under specific conditions.
- Visual inspection. Locate the secondary air injection switching valve B (often near the exhaust manifold or SAI pump). Inspect the harness and connectors for corrosion, broken insulation, rubbing on brackets, or water/oil intrusion.
- Verify power and ground. With the key on, use a multimeter to check for proper voltage and ground at the valve B connector according to the wiring diagram. A missing power or ground points to a fuse, relay, or wiring issue upstream.
- Check circuit continuity. With the connector unplugged and battery disconnected, test resistance of the control wire between the valve and ECU. High resistance or an open reading indicates a broken wire or bad connection.
- Test the valve coil. Measure resistance across the valve’s electrical terminals. Compare to spec. An open circuit or very low resistance (shorted coil) means the valve is faulty.
- Command the SAI system on (if possible). With a bidirectional scan tool, command the SAI pump and valve B on. Listen for the pump, feel or listen for valve operation, and monitor voltage at the connector. If the ECU commands it but the valve doesn’t respond, the fault is likely in the valve or wiring.
- Inspect related fuses and relays. Check the SAI fuse and relay, especially if you find no power at the valve. Replace any blown fuses and investigate why they blew (shorted wiring or component).
- Check Mode $06 data (if available). Some vehicles store SAI monitor test results in Mode $06. Reviewing this can show if the system is marginal or intermittently failing before the code sets.
- Clear codes and road test. After repairs, clear all codes and perform a cold start drive cycle. Verify the SAI monitor completes and P0416 does not return.
Pro tip: If you find green corrosion or water in the connector, don’t just clean it and move on. Moisture often wicks up the wire under the insulation. Cut back the harness until you see clean copper and use proper sealed butt connectors or heat-shrink solder joints.
Possible Fixes & Repair Costs
The actual repair for P0416 depends on what you find during diagnosis. Common fixes include repairing or replacing damaged wiring to the switching valve B, replacing the valve itself, or addressing a faulty relay or fuse. In rare cases, an ECU driver issue may require control module replacement and programming.
- Wiring/connector repair: $50–$250 depending on severity and labor time.
- Switching/combination valve B replacement: Typically $150–$450 parts and labor.
- SAI pump or relay replacement (if related): About $200–$600 depending on vehicle and pump location.
- ECU/PCM repair or replacement (rare): $500–$1,200+ including programming.
Costs vary based on your vehicle make, labor rates in your area, and whether you use OEM or aftermarket parts. On many vehicles, P0416 can be resolved on the lower end of that range with proper electrical diagnosis instead of guessing and throwing parts at the problem.
Can I Still Drive With P0416?
In most cases, you can continue driving with P0416 without immediate risk of engine damage. The code is emissions-related and usually doesn’t affect normal driving once the engine is warm. However, you may notice slightly rougher cold starts and a stronger exhaust smell for the first minute or two after startup. The bigger concern is that your check engine light will stay on, and you’ll likely fail an emissions or inspection test until the issue is fixed and the SAI monitor runs successfully.
What Happens If You Ignore P0416?
If you ignore P0416 long-term, you risk failing state inspections, running with a constant check engine light (which can hide new problems), and potentially allowing corrosion or wiring damage to spread. In some climates, water-intrusion issues that trigger P0416 can eventually affect other circuits if not repaired properly.
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
- P0416 indicates an electrical problem in the secondary air injection switching valve B circuit.
- The issue is usually in the wiring, connector, or the valve itself, not always the pump.
- You can typically drive with this code, but you’ll likely fail emissions testing.
- Proper diagnosis with a multimeter and wiring diagram saves money versus guessing at parts.
- Fixing P0416 restores proper cold-start emissions control and clears the check engine light.
Vehicles Commonly Affected by P0416
P0416 shows up on a wide range of OBD-II vehicles that use electric secondary air injection systems. It’s especially common on:
- GM vehicles (Chevrolet, GMC, Buick, Cadillac) with V6 and V8 engines using electric SAI pumps.
- Volkswagen and Audi models where moisture and corrosion in SAI connectors are frequent issues.
- BMW and Mini vehicles with complex SAI plumbing and tight engine bays that stress wiring.
- Toyota and Lexus models equipped with SAI systems on certain V6 and V8 engines.
- Some Ford and Mazda platforms using shared SAI components and harness routing near the exhaust.
Even if your exact vehicle isn’t listed, any car or truck with a secondary air injection system and a switching valve “B” can set P0416 when the circuit goes out of spec.
FAQ
Can I clear P0416 and keep driving without fixing it?
You can clear the code, but it will almost always return once the ECU runs the SAI self-test again, usually after a cold start drive cycle. Driving without fixing the root cause means your check engine light will keep coming back and you may fail emissions testing.
Is P0416 serious enough to damage my engine?
P0416 by itself is not typically an engine-damaging code. It affects the emissions system, mainly during cold starts. While it won’t usually hurt the engine, it can mask other problems if you get used to ignoring the check engine light, so it’s still important to address it.
How do I know if the switching valve B is bad or if it’s just wiring?
You’ll need to test both. Measure resistance across the valve’s terminals and compare to spec, then verify power, ground, and continuity on the control wire. If the wiring checks out and the valve coil is open or shorted, the valve is bad. If the valve tests good but you have voltage or continuity issues, the wiring or connector is the culprit.
Can a bad secondary air pump cause P0416?
Indirectly, yes. A failing pump can blow fuses or overload circuits that share power or ground with the switching valve B, which can lead to P0416. However, P0416 specifically points to the valve B circuit, so you should test the pump, relays, and valve wiring before replacing any major components.
Does P0416 always mean I need to replace the ECU?
No. ECU failure is one of the least common causes of P0416. Most of the time, the issue is a corroded connector, damaged wiring, or a failed switching valve. Only after confirming that power, ground, wiring, and the valve itself are all good should you consider an ECU driver fault, and even then it’s wise to have a professional confirm it.