P0413
PowertrainSecondary Air Injection System Switching Valve A Circuit Open
Most owners never notice anything wrong with the car itself. The warning light comes on, the engine drives normally most of the time, and the only clue might be a slightly rougher idle for the first couple of minutes after a cold start. Behind that light, the ECU has spotted an open electrical circuit on the switching valve that controls the secondary air injection system. That valve is meant to let fresh air into the exhaust during cold starts to clean up emissions before the cat is up to temperature, and when the circuit reads open, the ECU can't trust it's doing the job.
ⓘ Information only. This page provides general educational information about fault code P0413. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P0413 mean?
P0413 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Secondary Air Injection System Switching Valve A Circuit Open.
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • Engine warning light on, usually with no obvious change in how the car drives
- • A slightly rough or lumpy idle for the first minute or two after a cold start, then it clears
- • Occasional whirring or buzzing from the air pump area on start-up, or sometimes no pump noise at all when there should be
- • Very minor drop in fuel economy on some cars, often too small to spot
- • Hard starting or a brief stall on a cold morning on certain vehicles
- • No symptoms whatsoever beyond the light on a lot of cars
Possible causes
Causes commonly associated with P0413, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Corroded or seized switching valve, by far the most common cause, especially on cars that do lots of short cold runs where moisture sits in the system
- 2. Damaged or chafed wiring to the valve, or a connector that's gone green with corrosion. The valves often live in exposed spots under the bonnet
- 3. Blown fuse feeding the secondary air injection circuit, quick to rule out and cheap to fix
- 4. Failed or seized air injection pump, which can take the valve and its circuit down with it
- 5. Check valve gone faulty and letting condensation or exhaust gas back into the valve, corroding it from the inside
- 6. ECM driver circuit fault, rare, and only worth considering once everything else checks out
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Read the codes and freeze frame data, then check whether the fault is permanent or pops up only on cold starts. That tells you a lot about whether you're chasing moisture or a hard electrical fault
- 2. Get the connector off the switching valve and inspect it properly. Corroded pins and crumbly wiring are the usual story here, and a cleaned-up or repaired connector fixes a fair share of these
- 3. Check the fuse for the air injection circuit before you go any further, it costs nothing to rule out
- 4. Measure the valve resistance with a multimeter. Typical range is around 5 to 30 ohms depending on the car. An open reading confirms the valve coil has failed
- 5. Check for battery voltage at the connector with the ignition on, so you know the supply side is actually feeding the valve
- 6. If wiring, fuse and voltage all check out, command the air pump and valve through diagnostic software and listen for the pump and watch the live data to confirm whether the valve is actually responding
Common questions about P0413
If I clear the code, will it actually stay gone? +
Depends entirely on why it set. If it tripped because of a one-off bit of frozen condensation on a cold morning, clearing it and letting things dry out may keep it away for weeks. But a corroded valve or a chafed wire is a physical fault, and the light will be back within a handful of cold starts. Clearing the code is a useful test to see how quickly it returns, not a fix. If it's back within a day or two, you've got a hard fault that needs sorting at the valve or wiring.
What's the harm if I just leave it? +
Mechanically the car is fine to keep driving in the short term, because the secondary air system only does its job for the first minute or two of a cold start. The catch is emissions. With the system not working you're pumping dirtier exhaust until the cat warms up, and over a long stretch that extra unburnt fuel and soot is hard on the catalytic converter. On most cars it won't leave you stranded, but it will keep the light on and it's not doing the cat any favours.
How quickly do I need to deal with this? +
It's not a drop-everything job. There's no risk of the engine packing up, and you won't end up in limp mode over a P0413 on the vast majority of cars. Treat it as something to book in within the next few weeks, sooner if your MOT is due, since an illuminated warning light at the time of test can affect the result. If it's just a corroded connector, an hour at an independent garage and a few pounds in parts sorts it.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →