P2259: Secondary Air Injection System Control B Circuit Low
What to do
The car drives normally, with cold-start emissions affected. If both control circuits are faulted at once, ask for the shared supply and relay to be checked first — two valves failing together is much less likely than the one thing feeding both.
What this code means
The second secondary air control circuit reads below its valid range. A second circuit exists where the system has more than one controlled element — typically a switching valve as well as the pump, or separate paths feeding each cylinder bank on a V engine.
That distinction is useful when both A and B circuits fault together: separate valves rarely fail simultaneously, so the shared relay, supply or ground is the better first hypothesis. Where only B is faulted on a two-bank system, the fault is on one side and the search is correspondingly smaller.
Likely causes
Start here
- Wiring shorted to ground · moderate
- Faulty secondary air switching valve · moderate
Less common
- Failed secondary air check valve · moderate
- Corroded or loose connector · easy
- Damaged wiring harness · 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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What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
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