P2257: Secondary Air Injection System Control A Circuit Low
What to do
The car will drive normally; what is lost is emissions performance in the first minute of a cold start, which is enough to fail an emissions test. If a pump is quoted, ask that the check valve be replaced at the same time — a failed valve lets exhaust into the pump and is what usually kills it, so a new pump alone tends to fail the same way. And note that this can only be properly tested from a genuinely cold start, so an overnight stay may be needed rather than an appointment after a drive.
What this code means
The first secondary air injection control circuit reads below its valid range, normally a short to ground.
What the system does, and why it only runs for about a minute. A catalytic converter converts almost nothing until it is hot, and a cold engine is deliberately run rich, so the worst emissions a car produces all happen in the first minute after a cold start. Secondary air injection attacks both problems at once: an electric pump blows fresh air into the exhaust manifold, the unburnt fuel already there finds oxygen to burn with, and the resulting heat brings the catalyst to working temperature far sooner than exhaust alone would. Once the catalyst is lit the system has no purpose, so it shuts off. It runs for roughly thirty to ninety seconds after a cold start and then never again until the engine has fully cooled.
Two practical consequences follow from that, and both catch people out:
- It can only be tested at a genuine cold start. A car that has driven to a workshop cannot be assessed, and neither can one that has been idling while other work was done. The test needs the engine properly cold, which usually means overnight. This is the same constraint as the cold-soak check at P2199 and it has the same effect: a fault that looks intermittent is a test that gets one chance per day.
- The noise is normal. These pumps are loud — a distinct whirring or buzzing from the engine bay for the first minute after a cold start. It is regularly reported as a fault. What is worth noticing is the absence of that noise on a car that used to make it.
The failure that costs money is upstream of the electrics. The check valve between pump and exhaust exists to keep hot, corrosive exhaust gas out of the pump; when it fails, exhaust and its moisture reach a plain electric air pump that was never built for either, and the pump corrodes and eventually seizes. A seized pump is usually the symptom and the check valve is usually the cause — so fitting a new pump without replacing the valve simply destroys the new one too. A short to ground in this circuit is frequently a pump whose windings have gone that way.
Likely causes
Start here
- Wiring shorted to ground · moderate
- Seized secondary air injection pump · moderate
- Failed secondary air check valve · moderate
Less common
- Faulty secondary air injection relay · easy
- Corroded or loose connector · easy
- Damaged wiring harness · moderate
Symptoms
Components involved
Information, not instruction
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Community experience
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