P0491 Fault
12-23-2015, 09:54 AM
#1
P0491 Fault
Hi all,
Looking for some pix of vacuum lines etc to daignose, P0491-Secondary Air Injection System Bank .
Fuse is good... Can clear fault comes back in 2-3 weeks, seems like after hard acceleration but cant swear to that..
Runs smooth, pulls strong, no issues at all.. CEL just bugs me and I need to fix this...
Thanks
Pup
Looking for some pix of vacuum lines etc to daignose, P0491-Secondary Air Injection System Bank .
Fuse is good... Can clear fault comes back in 2-3 weeks, seems like after hard acceleration but cant swear to that..
Runs smooth, pulls strong, no issues at all.. CEL just bugs me and I need to fix this...
Thanks
Pup
07-10-2017, 11:25 AM
#2
Intermediate
P0491 & P0492 2006 V6 955 Cayenne 95k miles
Had these error codes plus P2235 & P2237 and the dreaded CEL light on the dash. I bought this vehicle CHEAP, it had low miles was well kept and had immaculate service performed. It has been an extremely good and reliable vehicle. I bought hoping to do alot of DIY projects and maintenance.
After extensive reading on this forum which is filled with tons of valuable information, I learned what the problem was concerning these codes and what to do to repair the problems.
In my case it was cracked (all of them in the engine bay) vacuum lines AND a split diaphram in the AOS (which is located on top right (passenger) bank rear of top of engine). It is important to remove the AOS as opposed to attempting to open it while still mounted to the engine. You can remove it by pressing the fittings on each end of the plastic hoses and unscrewing the bolt directly beneath the AOS. Be very careful as you do this as to not cause cracking of those hoses. Once off, open the AOS from the bottom by carefully using a flat head screw driver through the bottom of each tab hole pressing outward and releasing the top cover at each tab. Once open, replace the diaphram with one purchased at vanos-bmw.com you can surf the site to find the right one.
I replaced my evap purge valve (but Im not so sure I had to) and in the process snapped 1 very small diameter plastic tube/hose underneath it. There are 2 of these in that vicinity so be very careful when replacing the evap valve.
Ok, so tracking the vacuum leak. Once I had about an hour to study the engine bay, it wasnt very difficult to find all the lines and which ones were cracked. What you are looking for are cracks in the plastic tubes where they mount onto a fitting. As most have stated, the heat cool cycles in the engine bay cause these lines to become brittle over time and crack at their most stressed point (where they mount onto a fitting). Along the right bank (passenger side of engine) is where most to all of the vacuum lines reside. They are plastic and easy to tell them apart from hoses. I simply replace them all with rubber hoses (I think 3/8" since it was the same size as the plastic lines). I used hose clamps and was careful not to over tighten to crush any plastic fittings. I also made sure there were no crimped rubber hoses bending them for nice gentle curves. I wrapped everything up and cleared the codes. Ran it for a few days and darn it if the 0491 and 0492 code didnt reappear with a slightly rough running engine. Darn it.
I went back to the engine compartment and studied everything I did and i appeared fine...until I saw the final plastic line at the end of a larger rubber hose (not my work but original to the engine) as it ran through the fire wall again the right bank side and just behind window washer fluid reservoir. There is only 1 or 2 lines that run through the fire wall at this location and only 1 that has a bigger rubber hose connected to the plastic line that runs through the fire wall and there it was....the plastic line as it mounted onto the plastic fitting that connected it to the rubber hose was cracked. I really didnt wish to take the wipers off and all the plastic associated with that area so I decided to carefully cut the plastic line just below where it 'stretched' onto the fitting and subsequently cracked. I removed the clamp on the rubber hose, then removed the plastic male/male fitting from it. I slipped the plastic hose end that I newly cut into the rubber hose and then slipped the clamp back to its original position holding the plastic hose into the rubber hose. Started the engine and there were no vacuum leak sounds whatsoever. I cleared the codes and have been enjoying the codes not re-appearing for 3 weeks now. I think this solved the CEL issues. It runs so nicely, I cant believe it.
After extensive reading on this forum which is filled with tons of valuable information, I learned what the problem was concerning these codes and what to do to repair the problems.
In my case it was cracked (all of them in the engine bay) vacuum lines AND a split diaphram in the AOS (which is located on top right (passenger) bank rear of top of engine). It is important to remove the AOS as opposed to attempting to open it while still mounted to the engine. You can remove it by pressing the fittings on each end of the plastic hoses and unscrewing the bolt directly beneath the AOS. Be very careful as you do this as to not cause cracking of those hoses. Once off, open the AOS from the bottom by carefully using a flat head screw driver through the bottom of each tab hole pressing outward and releasing the top cover at each tab. Once open, replace the diaphram with one purchased at vanos-bmw.com you can surf the site to find the right one.
I replaced my evap purge valve (but Im not so sure I had to) and in the process snapped 1 very small diameter plastic tube/hose underneath it. There are 2 of these in that vicinity so be very careful when replacing the evap valve.
Ok, so tracking the vacuum leak. Once I had about an hour to study the engine bay, it wasnt very difficult to find all the lines and which ones were cracked. What you are looking for are cracks in the plastic tubes where they mount onto a fitting. As most have stated, the heat cool cycles in the engine bay cause these lines to become brittle over time and crack at their most stressed point (where they mount onto a fitting). Along the right bank (passenger side of engine) is where most to all of the vacuum lines reside. They are plastic and easy to tell them apart from hoses. I simply replace them all with rubber hoses (I think 3/8" since it was the same size as the plastic lines). I used hose clamps and was careful not to over tighten to crush any plastic fittings. I also made sure there were no crimped rubber hoses bending them for nice gentle curves. I wrapped everything up and cleared the codes. Ran it for a few days and darn it if the 0491 and 0492 code didnt reappear with a slightly rough running engine. Darn it.
I went back to the engine compartment and studied everything I did and i appeared fine...until I saw the final plastic line at the end of a larger rubber hose (not my work but original to the engine) as it ran through the fire wall again the right bank side and just behind window washer fluid reservoir. There is only 1 or 2 lines that run through the fire wall at this location and only 1 that has a bigger rubber hose connected to the plastic line that runs through the fire wall and there it was....the plastic line as it mounted onto the plastic fitting that connected it to the rubber hose was cracked. I really didnt wish to take the wipers off and all the plastic associated with that area so I decided to carefully cut the plastic line just below where it 'stretched' onto the fitting and subsequently cracked. I removed the clamp on the rubber hose, then removed the plastic male/male fitting from it. I slipped the plastic hose end that I newly cut into the rubber hose and then slipped the clamp back to its original position holding the plastic hose into the rubber hose. Started the engine and there were no vacuum leak sounds whatsoever. I cleared the codes and have been enjoying the codes not re-appearing for 3 weeks now. I think this solved the CEL issues. It runs so nicely, I cant believe it.
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Masalare993 (03-22-2020)
03-22-2020, 05:20 PM
#4
Nice job. I am trying to fix mine and I will make sure to check for cracks and vacuum leaks. Wondering if you have any additional fault codes?
I clear all codes and after running with the original P0492 for a while I get P0421 and P1033.
I clear all codes and after running with the original P0492 for a while I get P0421 and P1033.
03-31-2020, 06:02 PM
#5
P0491 and P0492 typically come up after the air pumps grenade themselves and their fins get sucked into the tubes and jam the one way valve attached to the back of the engine. The valves are challenging to reach but can be removed from underneath the truck with some extensions and E Torx sockets IIRC. You can try to clean them out but in my case it didn't work. If you remove the entire SAI system you'll have to make block off plates and get a tuner to shut the system off and that will keep the codes from coming back. I haven't had the time to get back under mine and remove the valves to take them to a machinist to make block off plates. I just had my tuner turn them off.