Help please! P0491 and P0492

[geno]

I've been fighting these P0491 and P0492 (Secondary Air System Bank 1 and 2) codes for 3 months now.
So far, I have replaced the Sec. air pump (#1, bottom image), the air valve (gray, no number) and the elec control valve (1, top). Also replaced all the little vacuum tubes I could see (items 10, 11, 12 - top image). I am completely lost at this time and need to pass emissions soon. If anyone has any ideas (short of the dealer) - I'm wide open. TIA!

[geno]

I've been fighting these P0491 and P0492 (Secondary Air System Bank 1 and 2) codes for 3 months now.
So far, I have replaced the Sec. air pump (#1, bottom image), the air valve (gray, no number) and the elec control valve (1, top). Also replaced all the little vacuum tubes I could see (items 10, 11, 12 - top image). I am completely lost at this time and need to pass emissions soon. If anyone has any ideas (short of the dealer) - I'm wide open. TIA!

Just a little bit of history:
Valve cover gaskets replaced 2 years ago
Intake manifold gaskets replaced 5 months ago
OSV and a bunch of misc. gaskets and o-rings replaced 5 months ago
MAF replaced about a year ago
TIA

[geno]

Anyone?

[sanjoses2k]

I found the following via a Google search... not a fix, but perhaps a little bit more info on how the system works?

"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.

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 should be able to feel and hear the pump running at startup

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, 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."

[geno]

I found the following via a Google search... not a fix, but perhaps a little bit more info on how the system works?

"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.

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 should be able to feel and hear the pump running at startup

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, 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."

Thanks! I've seen that one, as well as a few similar explanations. I have replaced all the major components (in yellow circles) of the system. Still only the same 2 error codes appear. Ican hear the pump run and stop within a minute of cold start, which is as expected. CEL is still ON.

[323I Junkie]

Have you done a systematic diagnosis. Have you disconnected anything and checked for actual flow?

If not, you need to start there.

Also, there is obviously a sensor to check for said flow that is being overlooked. I will go check mine out tommorrow and examine the system The key lies in the bank 1 and 2 thing....I am thinking voltage is not present when power is requested ...somewhere

[geno]

All right! Took the car to the stealer to get my Instrument Cluster replaced under BMWNA goodwill warranty, and asked them to troubleshoot the CEL for me.

They spent close to 3 hours on it and have found the problem. Since I've replaced all the components in that section, they checked for power to the air pump - none present. Cheched for power at air pump relay. REMOVED PASSENGER SEAT AND TRIM PANELS. PULLED CARPET UP AND FOUND 50 AMP FUSE BLOWN. Replaced fuSe, cleared fault, test drove. OK at present time.

So, there IS a fuse under the passenger seat? Well, I could've saved myself $300. I hope this helps someone out.
Gene

[geno]

..... The key lies in the bank 1 and 2 thing....I am thinking voltage is not present when power is requested ...somewhere

BULLSEYE!

[323I Junkie]

BULLSEYE!

Thanks. And thanks for your post. This is what makes forums so great. So we appreciaite you letting us learn from your experience. Your old air pump probably blew that fuse. You replaced it, but fuse still blown.

Was your air pump REALLY loud before failure?

[geno]

Thanks. And thanks for your post. This is what makes forums so great. So we appreciaite you letting us learn from your experience. Your old air pump probably blew that fuse. You replaced it, but fuse still blown.
Was your air pump REALLY loud before failure?

I don't recall that it was that loud. I can hear it now even better than I remember. The dealer though it was a valve failure that popped the fuse.
I have saved all the parts - it would be good to test each to see which has caused the problem and which are good spare parts.
I had no idea there was a fuse under the carpet of the passenger seat area. Why couldn't they just use one of the fuse boxes, like normal people?

[crewdog843]

First: Congratulations on getting the problem fixed.

Second: Thanks for getting back to the board with the solution. So many times, folks come to us with the problem, and we come up with possible solutions, but in the end.....we never know if the solutions worked or failed as we never hear about it again. Your solution will enable others with similar issues to possibly save money, now that we know there is another fuse to look for, in one of the most unlikely places.

Peace of mind, isn't it wonderful!!!!

jake

[323I Junkie]

Why couldn't they just use one of the fuse boxes, like normal people?

Normal People Would put a circuit breaker, digital protection, and a fault code indicator in the fuse box

[rome2001]

yeah or else we are not normal people, we just drive bmws dam stelers you gotta love them 1 fuse replacment $300 what happend to beign honest at least i hour for fuse replacment.

[323I Junkie]

I dont think it was 300 for the fuse, I think it was an hour for the IC and some other stuff.

[geno]

I dont think it was 300 for the fuse, I think it was an hour for the IC and some other stuff.

the dealer claimed that it took them a while to troubleshoot the problem, and that's where the seat removal came into play. No way I would think of it. Asking around here didn't really help me either. I got a great hint, but there was nothing I could do about it. The fuse was $5.xx the rest was labor.

I'd love to see a diagram of that area with a fuse....
Gene

[geno]

First: Congratulations on getting the problem fixed.

Second: Thanks for getting back to the board with the solution. So many times, folks come to us with the problem, and we come up with possible solutions, but in the end.....we never know if the solutions worked or failed as we never hear about it again. Your solution will enable others with similar issues to possibly save money, now that we know there is another fuse to look for, in one of the most unlikely places.

Peace of mind, isn't it wonderful!!!!

jake

thanks! i am happy that this solved the problem (2 days and holding!)

[psjr]

I'd love to see a diagram of that area with a fuse....
Gene

Me too!

I spent some time on realoem this morning, but to no avail.

[rome2001]

i dont think BMW lets average guys like us use their secrets or else they wouldnt be called stellers or not make any money

[323I Junkie]

i dont think BMW lets average guys like us use their secrets or else they wouldnt be called stellers or not make any money

For 25 a day you can PDF access to anything a tech has access too

[jmiseo2008]

I hate to resurrect an old thread, but I have also been battling codes P0491 & P0492. Does anybody have any more information about where the fuse is located under the passenger seat? So far I've replaced the pump, valve, and hose leading from the pump to the valve. After doing this, the CEL went out for a few days, only to return. Hoping it was a fluke, I reset and cleared the code....of course it returned. Any ideas?

[HighandFast]

Anybody with a diagram that shows the fuse location? I have an e46 m3 throing the P0492 code.

[jmiseo2008]

I don't have a diagram, but was able to complete the repair and solve the problem. On my e38, the 50a fuse was located under the passenger seat. I have the part number and photo of it's location at home, but I think it might be in a different location for your car.

[HighandFast]

Thanks!

[bcain79]

I just replaced my valve gasket and put in new plugs now i'm showing the same codes. Any way to tell if it's the fuse prioir to pulling the seat?

[colbytwentytwo]

If you have a multi meter check for voltage at the secondary air pump connector. if no voltage is present then check for voltage at the relay and so on down the line. Do you have the ETM? (electronic troubleshooting manual)

It is very helpful in troubleshooting electrical problems and tracing back the source of power to a failure point.