I have a 1996 850 with approx 205k. Check engine light is on with a code of P0172. After looking around it seems it could be one of 3 things oxygen sensor, air mass inflow, or a vaccum. Is there any way to narrow it down? The car is running great so I don't get it. But, it won't pass emissions with the issue.
Thanks

 

from what l have learnt, to test a MAF sensor, turn on the car, put it to drive and see if the car stalls and shuts off, if it does that means the maf is good.for the vacuum leak, you might want to check the hoses for any cracks or if any looks brittled. for the oxygen sensor you might want to wait on some smart folks to give you clues on how to test if its good or bad.
is it a regular 850 or a turbo?

 

Hi Kaktus, I have the same year non/turbo. I just went through the same thing a couple of weeks ago. Everyone on this site was very helpful in leading me in the right direction. If you search these threads under P0172 you will find more information than you could imagine. In my case I always go the least expensive first, that would be the vacuum lines and elbows. Check your vacuum diagram located at the bottom left corner under the hood. I took a picture of it with my phone and then blew it up and printed it. Hard to see with glasses on and your head cocked! Anyway, If your not sure that these lines and elbows have not been changed out with your mileage change them! You will be looking for cracked or brittle vac lines and/or elbows and straight connectors. Don't necessarily expect to see the obvious crack! If an elbow is soft like a marshmello and pulls like a rubber band it is bad. Air seeping through that connector is all that it takes. After replacing, I disconnected the negative batt. terminal for a few minutes to reset the check light. Don't forget your radio code! Good luck!

 

Thank you for both of your replies. I'll take a look tomorrow and see if I can narrow it down. Is that something I can do myself, changing the lines?

 

I'd try to get my hands on an OBDII scanner and erase the codes. That way you don't have to worry about the radio code if you still have an OEM radio and you aren't erasing the engine management computers memory where it has to relearn your driving style.

 

pretty easy to change the lines but you have to make you get it right making sure you dont mix it up.

 

I checked the lines and they really don't seem to be the problem. I'm thinking it is more likely the O2 sensor. The car is my son's and it has to pass emissions in order to get the tags for it. Just don't want to spend a whole lot more of money as I just put a new radiator into it. We only plan on keeping it for about 6 more months. I'll replace the sensor, I think that one we can do, get the codes reset and hope for the best. Thanks for the info on not disconnecting the battery, that's good info to have!

 

That is a vacuum code. Not a MAF or O2 sensor code.

My cars have all be turbo (P2 style). When I had the code the vacuum line going to the base of the intake tube, near the turbo was off. If the car doesn't have a turbo, it may be another line related to the PCV system.

If you pull the battery cable to clear the code, it will have to go through a drive cycle before it will give a READY code and pass emmissions. Not sure about setting it with the obd-2 tool. At either rate, I have to drive 400 miles to get a READY output.

 

The car doesn't have turbo, so maybe that's why the vacuum line looked fine. I'll have time over the weekend to check it out some more. Appreciate the additional info on pulling the battery. May be doing some driving over the weekend as well.