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E46 Xi Forum
The E46 XI was produced from 01-05 in sedan and touring body styles. Powered by either a 2.5L inline 6 in the 325xi or a 3.0L inline 6 330xi. Discuss all thing about BMW AWD E46 'Xi' here.

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Old 03-30-2011, 04:57 PM   #1
Smittyjf
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P0491 and P0492 System works perfect

I'm baffled. About 3 weeks ago started getting Secondary Air codes P0491 and P0492 on my 05 325xi. Cleared them and 3 days later (Prob 3 cycles of error) SES came on again with same thing.
I troubleshooted every aspect of the system. Pump works fine (I check it on every cold start the past 3 weeks) and has strong airflow from it. The silver valve that opens and lets the air into the exhaust works perfect (Vac hoses are also fine and have strong Vac). The valve opens and closes with no problems when you connect and disconnect little vac hose and allows strong airflow into the exhaust.
The vac switch works fine and starts and stops the vac after about 1.5 to 2 min along with the SAP.
The only thing I have noticed is that after 1.5 minutes the silver valve seems to start to close before the SAP shuts off (Which it runs for about 15 to 20 seconds more) I can only assume that this is normal as you do not want exhaust backing through the SAP causing early failure.

If anyone has any ideas I'm interested. I did have o2 pre cat errors when I first cleared them 3 weeks ago, but they have not come back since.
The car only has 50,000 on it purchased in 10/04 so i don't think the o2's are bad, but that shouldn't throw SEC AIR codes unless i'm mistaken.

Smitty
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Old 03-31-2011, 07:32 AM   #2
Mark M
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I've never had this issue, but first ask yourself what would trigger these codes? Meaning what electrical sensor or fault would tell the computer to trigger those faults.

My guess is you might have O2 sensor issues. Reason - at startup isn't the O2 sensor looking for certain values from the exhaust gases to confirm the secondary air pump system is working? If the O2 is failed, wouldn't it potentially issue such a fault?

I could be wrong, but just a hunch.
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Old 03-31-2011, 10:25 AM   #3
lkchris
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That is ...

... VERY often codes indicate a symptom and not the disease.
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Old 03-01-2012, 07:49 PM   #4
Leathers
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I have exactly the same problem as Smittyjf on my 2004 325xiT...every SA system component works fine but I get codes P0491 and 2. If it is related to the O2 sensors, is there one particular O2 sensor that would cause this or do you have to change all 4?
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Old 03-01-2012, 09:24 PM   #5
e46alfonso
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i was going to make a thread about the P0491/0492 codes today, because i'm having the same problem. its driving me nuts, i can't get rid of them.

i doubt the O2 sensors have any connection with the SAP system. i have not replaced the sensors yet

my punp works fine, you can hear it from a block away, and there are no leaks. my CEL stays lit for 2 weeks and goes away by itself for 3 days
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Old 03-02-2012, 08:21 AM   #6
fastjasonbmw
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The non-return valve likes to freeze and/or stick, replace it (it's easy). Also remove the vacuum check valve by the vacuum solenoid (rear of intake manifold), at the dealer when we have secondary air issues, the vacuum check valve is always removed.
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Old 03-02-2012, 08:30 PM   #7
e46alfonso
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^^ thank you sir. that is a cheap part too.
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Old 03-07-2012, 09:15 PM   #8
boostedisbetter
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Quote:
Originally Posted by fastjasonbmw View Post
The non-return valve likes to freeze and/or stick, replace it (it's easy). Also remove the vacuum check valve by the vacuum solenoid (rear of intake manifold), at the dealer when we have secondary air issues, the vacuum check valve is always removed.
As in you just bypassed it, or replaced it?
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Old 03-08-2012, 10:29 AM   #9
bryan@bimmerworld
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Quote:
Originally Posted by Smittyjf View Post
I'm baffled. About 3 weeks ago started getting Secondary Air codes P0491 and P0492 on my 05 325xi. Cleared them and 3 days later (Prob 3 cycles of error) SES came on again with same thing.
I troubleshooted every aspect of the system. Pump works fine (I check it on every cold start the past 3 weeks) and has strong airflow from it. The silver valve that opens and lets the air into the exhaust works perfect (Vac hoses are also fine and have strong Vac). The valve opens and closes with no problems when you connect and disconnect little vac hose and allows strong airflow into the exhaust.
The vac switch works fine and starts and stops the vac after about 1.5 to 2 min along with the SAP.
The only thing I have noticed is that after 1.5 minutes the silver valve seems to start to close before the SAP shuts off (Which it runs for about 15 to 20 seconds more) I can only assume that this is normal as you do not want exhaust backing through the SAP causing early failure.

If anyone has any ideas I'm interested. I did have o2 pre cat errors when I first cleared them 3 weeks ago, but they have not come back since.
The car only has 50,000 on it purchased in 10/04 so i don't think the o2's are bad, but that shouldn't throw SEC AIR codes unless i'm mistaken.

Smitty
We hear people with this problem often, and I've dealt with it myself. Typically, on our vehicles, that system if fully removed, but for most of us, that's not always the best option. I own an E46 xi with 60,000 miles on it, hardly enough to gunk the systme up as some vehicles see. Not sure you're mileage though. Generally, it's not the pump at all, and as you've heard, the pump cuts on and cuts off once it's warmed up enough, so it's doing its job.

When you say you checked the vacuum hoses, I just wanted to make sure you checked the one that is on the back of the intake manifold. You have to remove the cabin filter and tray to access this, so most people miss it. The hose is small diameter and makes a 90 degree bend to connect, so that, plus heat and a small hose, usually leads to it cracking. I've fixed two E46s just by replacing that hose. Easy to feel down there and see if it's broken. Good luck!
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Old 03-29-2012, 04:30 PM   #10
Leathers
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Quote:
Originally Posted by bryan@bimmerworld View Post
We hear people with this problem often, and I've dealt with it myself. Typically, on our vehicles, that system if fully removed, but for most of us, that's not always the best option. I own an E46 xi with 60,000 miles on it, hardly enough to gunk the systme up as some vehicles see. Not sure you're mileage though. Generally, it's not the pump at all, and as you've heard, the pump cuts on and cuts off once it's warmed up enough, so it's doing its job.

When you say you checked the vacuum hoses, I just wanted to make sure you checked the one that is on the back of the intake manifold. You have to remove the cabin filter and tray to access this, so most people miss it. The hose is small diameter and makes a 90 degree bend to connect, so that, plus heat and a small hose, usually leads to it cracking. I've fixed two E46s just by replacing that hose. Easy to feel down there and see if it's broken. Good luck!
I've checked that my car has good vacuum suction, so by default, the hoses should be ok. What else can it be?
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Old 03-29-2012, 04:45 PM   #11
bryan@bimmerworld
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Could be, but have you reached around the back of the intake manifold to feel that small hose? I had vacuum as well but a small slit in that hose. Just a good starting point I feel and it worked for me.
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Old 03-29-2012, 06:45 PM   #12
Rickna
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Quote:
Originally Posted by fastjasonbmw View Post
The non-return valve likes to freeze and/or stick, replace it (it's easy). Also remove the vacuum check valve by the vacuum solenoid (rear of intake manifold), at the dealer when we have secondary air issues, the vacuum check valve is always removed.
I had the same issues. I replaced the check valve and dry-rotted vaccum lines.
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Old 03-31-2012, 10:57 AM   #13
Leathers
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I can't tell whether the hoses are shot or not. They look fine. Taking my car to the Indy next week, hopefully he'll find the problem. I think it probably is the hoses but I can't find any issues. I'll report back with what he finds.
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Old 04-14-2012, 07:21 PM   #14
Leathers
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Indy can't find the problem...everything is working fine. He's guessing that the check valve may not be opening in a timely fashion and triggering the code. Such a finicky system this!
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Old 04-15-2012, 12:04 AM   #15
colo330xi
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I have seen reports of the ports in the header/cyl head for the SAP clogging. You might try running some seafoam in the hose from the SAP into the exhaust.(before you go throwing parts at it)

Here's the thread.

http://forum.e46fanatics.com/showthread.php?t=891097
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Old 04-15-2012, 07:00 PM   #16
Smittyjf
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Update from a year ago......The car has 60,000 miles on it now, Still getting the SES light.
I Checked the valve and it opens with the vacuum for the whole 90 second cycle then closes and the pump goes off right after that. I checked it off the manifold with no vacuum and it stays closed with no blowback.
Vacuum at the valve is aprox 15lbs which is normal during whole cycle.

Here is the difference wether I get the SES light... I only get sec air codes if I don't let it sit and idle through the cycle. If I put it in drive and go, I'll get the SES.
This was the only way I could get past emissions, but the problem still exists. I trued the sea foam trick 3 times also.
I can't imagine the O2 sensors are bad but who knows, that's the last piece of the puzzle with every other component working.
Does the O2 sensor detect the failure?
Smitty

Last edited by Smittyjf; 04-15-2012 at 07:03 PM.
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Old 04-16-2012, 12:46 AM   #17
colo330xi
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The O2 sensor is the one throwing the failure to the DME. It is basically saying "not enough oxygen is in here, the SAP is running, there should be more oxygen than normal"

If the O2 sensors were outright bad, you should be throwing other codes while running. They shouldn't be used up/erroring out at 60k miles. If you have any way of logging/ watching the O2 sensor values as the car warms up, that might be helpful. I have a cheap BT obd2 interface and android app for these sort of issues.
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Old 04-16-2012, 11:27 AM   #18
SamDoe1
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Quote:
Originally Posted by colo330xi View Post
The O2 sensor is the one throwing the failure to the DME. It is basically saying "not enough oxygen is in here, the SAP is running, there should be more oxygen than normal"

If the O2 sensors were outright bad, you should be throwing other codes while running. They shouldn't be used up/erroring out at 60k miles. If you have any way of logging/ watching the O2 sensor values as the car warms up, that might be helpful. I have a cheap BT obd2 interface and android app for these sort of issues.
What BT interface do you have?
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Old 04-16-2012, 06:34 PM   #19
colo330xi
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I have a boring amazon ELM327 BT interface, works fine with torque app.

http://www.amazon.com/BAFX-Products-...4618986&sr=8-2

That is what it looks like. I paid somewhere around that 22 dollar mark. You get all sorts of live data, engine temp, MAF flow rates O2 sensor voltages.
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