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E46 (1999 - 2006)
The fourth generation 3 Series (E46 chassis) was introduced in 1999 and set the standard for engineering and performance during it's years of production including being named to Car & Driver's 10 best list every one of those years! ! -- View the E46 Wiki

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  #1  
Old 11-14-2008, 05:22 PM
Bobk528 Bobk528 is offline
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P0491 code - secondary air system

I recently had a mechanic replace the secondary air pump, air valve, electric control valve, and rubber hose (total cost of $1050) because a P0491 and P0492 Check Engine code appeared. After the mechanic cleared the codes, the car ran for 1 day before the Engine light and same codes (P0491 and P0492) returned

There is nothing else to replace. Anyone have any suggestions on how to resolve this code problem?
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  #2  
Old 11-14-2008, 05:30 PM
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Solidjake Solidjake is offline
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wow, thats nuts. changing that air pump would have fixed the problem. double check to see if you have any leaks
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  #3  
Old 11-14-2008, 05:39 PM
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KrisL KrisL is offline
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Sorry to hear that :/. I see you're in San Jose - may I ask what mechanic you went to?
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  #4  
Old 11-14-2008, 06:56 PM
toddkageals toddkageals is offline
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I got this same code when I changed my CCV valve. In changing the valve, I removed the intake manifold. On the back of the intake manifold (near the firewall) there was an electrical connector that I left disconnected. It's easy to do since you can't see it once the manifold is back on. You can feel it with your hand if you remove the microfilter housing. Should be easy to feel around back there and see if something is disconnected. Could also be a short in that wire I suppose. You might try a mechanic's mirror on a stick to be able to see back there.

Good luck.

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  #5  
Old 12-01-2008, 06:45 PM
jayton jayton is offline
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So how did it all turn out? Is the light still on? Have you rechecked the wires?
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  #6  
Old 12-10-2008, 05:14 PM
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mikevaquez mikevaquez is offline
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Have the same problem. I changed my secondary air pump and the check engine light came back on after 2 days. Anyone have an answer for this?
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  #7  
Old 12-21-2008, 03:18 PM
Bobk528 Bobk528 is offline
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P0344 - camshaft sensor, P0491, P0492

Several weeks ago, the OBD reader displayed three codes: P0344 - camshaft Position Sensor, P0491 and P0492, which are related to the secondary air system. Shortly after reading the codes, the car would not start.

My son replaced the OEM pulse generator/Camshaft position sensor and was able to get the car running. The codes were erased and have not returned.

Is there a direct relationship between the earlier diagnostic codes (P0491 and P0492) and replacing the camshaft position sensor (P0344)?
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  #8  
Old 04-27-2009, 07:06 PM
Bobk528 Bobk528 is offline
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Several months ago the check engine light returned with the same code numbers, P0491 and 0492. After searching the bulletin board, an independent BMW mechanic determined that the problem was isolated to the non-return valve, which is part number 11611312737 and according to Bav Auto, it cost $16.95 but the small plastic piece looks like it costs only 5 cents.
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  #9  
Old 06-12-2009, 08:02 PM
Bobk528 Bobk528 is offline
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The problem seem to be a 50amp fuse for the secondary air pump (fuse slot number 36). I went to AutoZone and paid $3 for the fuse, erased the code and the Check Engine light has not turned on for a week.
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  #10  
Old 12-04-2009, 12:05 PM
raeboo raeboo is offline
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saw this on e46 Fanatics:

Last November the Check Engine light appeared on a 2001 325Ci and the diagnostic code reader displayed P0491 and P0492. An independent mechanic replaced the secondary air pump, air valve, electric control valve, and rubber hose at a total cost of $1,050.

After the mechanic cleared the codes, the car ran for 1 day before the Engine light and same codes (P0491 and P0492) returned.

The Check Engine remained on until the mechanic recently searched a BMW bulletin board and determined that the problem was isolated to the non-return valve, which is part number 11611312737. According to Bav Auto, the part cost $16.95 but this small plastic piece looks like it only costs 5 cents. So far the Check Engine light has not returned. If you receive a P0491 and/or P0492 code, you may want to first look into replacing a $17 part.
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  #11  
Old 12-04-2009, 12:10 PM
jh jh is offline
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Did the tech clear the "adaptive" values... when clearing the codes? I had a recurrence of check engine light couple days after secondary air work on an E36... and when the tech cleared the "adaptive" values... it has not recurred.
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  #12  
Old 01-09-2010, 05:51 PM
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AlboBMW AlboBMW is offline
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I also had this morning, and it was really really cold when I started the car.

I checked the codes, then I went to the internet.

I found this
Quote:
Once you get fault codes, it does not automatically mean that you have to replace parts. The FC's simply mean that you have problems in the circuits mentioned(in your case the secondary air systems in banks 1 & 2). You still have to diagnose the cause of the problem before you replace parts if needed.
Sometimes you do not even need to replace anything(like when you just cut a vacuum hose with a loose end provided it still reaches its destination, or you just plug a connector that got loose).
Your problem is with the secondary air pump system(the system in general since it involves both banks). At cold engine startup, the pump runs for about a minute to provide extra air into the exhaust system so that unburned gases gets burned off in the catalytic converter as part of the emissions system.
The general overview of the system is this:
1) the pump is turned on by the engine computer (DME) at cold startup
2) the DME switches on the pump relay (usually found behind the glove box) which turns on the pump. The DME does its work properly when the 5 fuses in the main electronic box are not blown(the fuses are housed in a small box of 5 fuses). The small fuse box in turn is housed inside the big black box either on the left or right side of the engine compartment.
3) if the pump does not turn on at cold startup then there may not be power at the connector to the pump or the pump itself is bad (or the pump may turn slower due to low voltage supply or due to a bad pump motor); you can feel and hear the pump running it is at the right somewhat front area of the engine compartment
4) when running, the pump provides the air output thru a hose to a valve which is switched on by a vacuum switch solenoid (thru a small vacuum hose), usually the hose gets wornout and can no longer switch on the valve, sometimes the solenoid switch goes bad (this is at the left side rear end of the engine), sometimes the valve itself goes bad (you can test this by removing the valve, looking for free movement and functional testing by supplying vacuum to it)
5) when the valve is working properly, then the air supplied by the pump goes into the exhaust manifold and then the catalytic converter
6) the oxygen sensors before and after the catalytic converter monitors the situation during the brief span that the pump works (at cold startup) and then gives an OK or stores a fault as needed.
So you see, it is not a simple matter. But with the above data you can diagnose the problem and find out for yourself what the car needs. It can be a fuse, relay, valve, solenoid switch, vacuum hose, or pump. But definitely not 02 sensors.
http://en.allexperts.com/q/BMW-Repai...325i-P0491.htm

So I checked the hoses. The thin long one, runs all around the intake manifold into a insert into the manifold, behind the engine, under the cabin filter assembly. The hoses were fine. I erased the codes and hoped this was a one time glitch. I allowed the car to completely cool down --easy to do in 19 degree weather-- and I started the car. The code did not return and the secondary pump came on, then after 50 second I heard it wind down like usually.

I also checked the fuses, and they were fine.
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  #13  
Old 05-26-2010, 10:18 AM
gramirez gramirez is offline
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Question: My name is grace, i drive a 325ci 2001, having problems with code0491,0492, to replace the check valve, where does it go?
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  #14  
Old 05-26-2010, 10:49 AM
Starless Starless is offline
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Quote:
Originally Posted by gramirez View Post
Question: My name is grace, i drive a 325ci 2001, having problems with code0491,0492, to replace the check valve, where does it go?
I have a write up in my signature with some good resourses for you. See if that helps
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