Stephen Max

I've had my 545i for about three months now. Not long after I bought it, the check engine light came on with an increased emissions warning. I have a code reader, and the code was P0492, low secondary air flow, bank 2. After doing some research, found out it is usually caused by a cracked y-pipe, so I spent a weekend replacing the y-pipe and the driver's side valve cover gasket while I was at it. I now understand why dealers charge so much to do that job. Anyway, replacing the y-pipe did not solve the problem. The code came back after about a week. I would clear the code and it would come back every time after 3-5 days.

At the same time, I noticed that my battery was acting weak at startup, and if I didn't drive the car for several days I would have to put it on a trickle charger as the battery would lose its charge. So I ended up replacing the battery.

Lo and behold, the check engine light has not come back since then, and it has been three weeks. Why? My thought is that the secondary air pump takes a lot of juice to operate, and after startup the alternator was busy trying to charge the weak battery and the air pump either did not operate or operated weakly and did not generate enough pressure to open the secondary air valves and inject air into the exhaust. Perhaps there was enough pressure to open the right side valve, but not both, hence the warning concerning the left bank.

Anyway, if you are getting P0492 and your battery seems on the weak side, you might consider replacing the battery first before paying to have the secondary air system worked on.

zamestytel

Did you registered the battery?

Stephen Max

Yes, I had an indy shop do it.

EUAutoHaus

Did you reset the adaptions after changing the valve cover gasket? Perhaps the dealer did this for you? Did you inform them of previous work done? I have never seen battery registration fix an issue like you're saying. This would be because they most likely cleared your Error Memory and Error History, something your scan tool is incapable of doing correctly on this vehicle.

Stephen Max

I am not saying that battery registration fixed the issue. I am saying that a weak battery may have resulted in the SAP from operating at full power, resulting in insufficient airflow through both secondary air valves and triggering the code. What I do know is that I was getting the CEL before, even after replacing the y-pipe, and now it is gone. By the way, I have seen at least one other person, either on this forum or on bimmerforums, who had the same experience.

meatzorb

Did your code ever come back? I am having the same code. I have no Batt issues. The Y pipe appears to have no cracks. I am checking into the valve opening or not. I had changed the O2 sensor as well ( pre cat)

DBU

I believe that a weak battery will cause other, more or less unrelated, faults. These cars are very sensitive to variances in voltage and this is sometimes manifested in the strangest places.

deansimpson

+1 to this.
My battery was getting a little old and I started getting random errors that didn't seem to exists.
Replaced the battery and nothing since.

meatzorb

Did your problem ever ccome back after changing the battery?

panochote

I have the same issue. Here is what INPA scanned . . .

2761 SEKUNDAERLUFSTYSTEM Bank 2
P0492 LUFTSYTEM Bank 2

I read that it could be a variety of things from O2 Sensor to Secondary air Pump. The Service Engine Light has come on three times now. I know the dealer will just guess too and have me replace parts I do not need. Any thoughts here or may I ask for opinions and/or responses please.