# What does secondary air sys. flow too low mean ?



## The Other Tom (Sep 28, 2002)

My wife has a 2001 325i. The check engine light keeps coming on and the dealer has not been able to diagnose it. (OK, by the time I get it to the dealer, the light has gone out).
I finally broke down and bought a Peake code reader, which says F5 (secondary air system flow too low, cyl #1-3), and F6 (secondary air system flow too low, cyl# 4-6). Does anybody know what this really means ? Possibly bad air pump ?


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## RoyE46 (Jan 31, 2004)

The secondary air pump seems to usually fail because the exhaust check valve went first. This lets wet and corrosive exhaust into the air pump, which then fails. So if you replace the pump, do the valve too.


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## The Other Tom (Sep 28, 2002)

RoyE46 said:


> The secondary air pump seems to usually fail because the exhaust check valve went first. This lets wet and corrosive exhaust into the air pump, which then fails. So if you replace the pump, do the valve too.


Thanks, Roy. Anybody else have any ideas ?


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## vm (Jul 16, 2002)

The Other Tom said:


> Thanks, Roy. Anybody else have any ideas ?


Same thing happened to me and it was what Roy said. You can check the pump easily after a cold start just go close to it and hear if it sounds like a high pitch subtle whine (good) or make all kinds of weird noises (bad). It goes off by itself after about a minute. Solve the problem quickly because a rich mixture can clog the cat converters.


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## Alex (Mar 11, 2004)

This happened to me too. Dealer said the secondary air pump and valve need to be replaced and it's being done as I'm writing this. Took 3 weeks for the parts to get here, though. I don't know if it's related but my fuel economy went really down, dealer did not know if this is related to the faulty part.


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## The Other Tom (Sep 28, 2002)

Thanks for all the replies. I took my car in today and the service advisor said it was a bad diverter valve. They replaced it. He said they tested the air pump and it was ok :dunno: No check engine light...yet.


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