Engine code trouble

VinnieSquints · #1 (**permalink**) 02-12-2008, 01:17 PM

So I got the SES light yesterday and decided to check it out. I stopped at Advance Auto and they did their free check. the codes that came up were

P0492 secondary air system bank 1
P0491 bank2

Any help on what could cause those? The dealer said those codes meant nothing to them and I would have to use their diagnostics which takes them an hour.
Also, it's been really cold here lately. Snowin all day today. I heard that might cause the problem.

Manolito · #2 (**permalink**) 02-12-2008, 10:35 PM

I am not familiar with your engine. Do you have what appears to be a vacuum cleaner motor that draws fresh air and pumps it into your exhaust manifold as the car warms up? On the late e36s, it was at the rear passenger side corner of the engine compartment. I don't know where they would have put it on your car, but it has to be somewhere else.

If you find that motor/fan, that is your secondary air system. Those fans generally last 6-10 years. Before replacing it, make sure that it is getting power right after a cold start. The relay that powers it can also fail. Be careful removing the fan. On the e36, the soft rubber mounts for the fan are easy to rip in two if you don't hold them carefully while loosening the nuts.

The good news is - running without it will not hurt the car, it just makes a little extra CO during warmup.

VinnieSquints · #3 (**permalink**) 02-13-2008, 01:57 PM

I took your tips and went outside to eye things up. I heard the motor going and gave the hoses in the general vicinity a little adjusting to see if i had a leak somewhere. I didn't find anything odd (but it's raining, so I wasn't exactly thorough). Figurin Id just wait til it's a bit dryer, I went to turn off the car. And to my joy, found the light had gone out. So, we'll see what happens in the days to come.

Manolito · #4 (**permalink**) 02-13-2008, 11:01 PM

The usual failure mode for those fans is just like the failure mode in a cheap vacuum cleaner. The bushings on the motor get loose enough that the motor shaft can start to chatter. It makes a terrible racket for a couple of days until it seizes up. When it seizes, it can fry its relay. The relay is no big deal but that fan is expensive.

On an e36, it is not rebuildable. You cannot get the fan off the motor shaft to get to the bushing. I presume that the e46 is similar.

VinnieSquints · #5 (**permalink**) 02-14-2008, 12:54 PM

I'll keep my eyes and ears peeled in the future.