P2431: Secondary Air Injection System Air Flow Pressure Sensor Circuit Range/Performance Bank 1
What to do
The car drives normally. This one often means air genuinely is not reaching the exhaust rather than that the sensor is wrong — so ask for the check valve and the pipework to the exhaust to be inspected for blockage and carbon. Note that this system only runs for about a minute after a properly cold start, so testing it may need the car left overnight rather than an appointment after a drive.
What this code means
The secondary air flow sensor is reporting a figure the module cannot reconcile with what it commanded.
This is the code most likely to be reporting a real blockage rather than a sensor fault, for the reasons set out at P2430: the failures of this system are physical, and this is the only sensor positioned to see them. A reading of little or no flow while the pump is running is very probably true.
So the order that matters is to establish whether air is actually flowing before concluding anything about the sensor — and the check valve is the first thing to inspect, because when it fails it both blocks the path and destroys the pump behind it.
Remember too that the whole system runs only for a short period after a genuinely cold start, so any live testing needs an engine that has stood long enough. That constraint is at P2257 and applies to every code in this family.
Likely causes
Start here
- Failed secondary air check valve · moderate
- Blocked secondary air pipework · moderate
- Seized secondary air injection pump · moderate
Less common
- Faulty secondary air flow sensor · moderate
- Faulty secondary air switching valve · moderate
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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