Chicken Bone

CEL on my 2004 530i has been on for 3 years. Initially was P0174 (Secondary Injection System), so I changed the check valve, and finally the actual pump which was full of water and had failed. P0174 went away but still have CEL. Now the codes are P1412, P0171 and P0174. I knew I had a valve cover gasket leak because I've had small amounts of oil on my manifold cover. So... thinking this was also causing a vacuum leak I changed gaskets yesterday. The old gasket and the valve seals were really bad and plasticized. Today, I reset CEL and I'm still getting the same three codes. Is there any significance between the P1412 (Secondary Air Leak) and the Lean Codes? In other words, could a leak in the secondary air system cause a vacuum leak? Car is running fine other than an occasional loss of power when my fuel tank is low (like its not getting any fuel)...which usually goes away after restarting. Sorry for the longwinded post, just trying to self-diagnose.

Chicken Bone

OK, so today I parked on an incline and smellled oil burning. THis is an old problem that I thought would have been cured by the new valve cover gasket. Any other ideas about where oil could leak out?

KyleB

M54 oil leaks usually come from valve cover gasket, oil filter housing gasket, rear main seal, oil pan gasket. If it's puking that bad and you've already done the valve cover gasket, the next place I'd go is the oil filter housing gasket. It is a $5 part and can be done in less than an hour.

as for those P0171 and 174 codes, it's probably time to do a smoke test. you likely have a vacuum leak that you haven't been able to find.

good luck, please post back when you have it solved.

Chicken Bone

Ok, I think I found the cause of the P1412 code (Secondary Air - Large Leak code) The tube from the Secondary Air check valve to the pump was completely disconnected! I changed out a faulty valve and pump last year, but I guess I didn't push hard enough on the connector to get the click.


Question: Is this Secondary air system related at all to the vacuum system? I've read numerous times that the Secondary Air PUmp can be eliminated altogther and car will run fine. However, I also have read conflicting accounts that the Secondary Air hose can leak and cause Lean Codes.


So confused.

KyleB

Yes, you can buy and install an emulator and completely remove the secondary air pump completely.

The entire purpose of the secondary air system is to inject fresh air into the exhaust stream forward of the oxygen sensors during cold starts only. this dilutes the exhaust mixture, introduces more oxygen into the exhaust stream. leaning out the exhaus stream forward of the primary 02 sensors and catalytic converters brings the 02 sensors online quicker, which then produces a 'cleaner' fuel mixture and less emissions. as soon as the 02 sensors come online, that secondary air pump shuts off completely.

so yes, theoretically a bad pump could cause lean mixture codes if for some reason it is injecting fresh air into a system that is also being leaned out by the 02 sensors. if you found a disconnected pipe on the pump, that very well could have been the culprit. make sure everything is secured, clear your codes, put a couple hundred miles on the car and see if that takes care of it.

good luck.

Chicken Bone

OK thanks KyleB. I kinda understand. I reset the codes following the VCG replacement, and they immmediately returned. With the SAP hose disconnected, I assume the check valve would be open all the time for un-metered air to enter. I guess I need a lesson in the difference between secondary air. I always thought it was a whole different system than combustion air. Similarly, I still dont get how a VCG leak can affect the air in the combustion chamber. Didn't they used to actually vent valve cover to the atmosphere? Anyway, thanks again. I'll post again in 200 miles or so.

Chicken Bone

Update: Ok, so I removed the front passenger wheel and found the secondary air hose (from pump to check valve) completely disconnected at the pump. I reconnected it and then went to my local mechanic to reset CEL. As before, he clears the codes (P1412, P0171, P0174) but CEL nevers goes out. Then immediately the codes reappear! Kinda confused. Isn't there a drive cycle that has to be gone through before codes return, and why did the CEL never go out?

KyleB

are you sure he's actually clearing them out? doesn't sound like it.

Chicken Bone

No, I'm not sure. I watched his computer screen and saw them go away, but CEL never went out. Then the codes returned in 30 seconds. The last time, the car wasnt even running. I'll go somewhere else and try. Ugh!

Chicken Bone

Got CEL turned off yesterday. 60 miles later, it came back on. Going to scan for codes now. Hopefully at least the P1412 went away. Will update soon.