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I have a 1999 bmw 540i auto with a problem please help. could be o2 sensor????

4020 Views 5 Replies 4 Participants Last post by  1Dreamer
Hi thanks for looking. I bought a 540i last thrusday. the owner told me he had someone plug it into a diagnstics machine and it needs new 02 sensors? can anyone tell me what they are and also what result that means to me and how much? also the air flow meter connected to the air intake was not plugged in! he said he unplugged it when he plugged the diagnostics machine in. Now I know it has a problem.

I took his word for it and bought it cos it ran ok on the test drive. since then it has ran well, i put some redex in a tank full of fuel and that seemed to help the mpg . . . . . .

since then this morning it didnt open on the key fob. so i used the key manually, i only have one key, in a pretty bad condition! an hour later or so the key didnt work when i tried to open it and all the engine wouldnt start, like it had a flat battery, i jumped started it, it seemed to run fine when i drove straight to kwit fit, the guy changed the battery, started it and the engine revved up to 1500rpm then it went straight out or off. he done it three or four times and it kept doing it. this was the first time it started and then cut straight off. he said it could be the battery he didnt have another one at the garage. i went to another garage and they checked my batt and it was fine!! but the problem persisted with my battery or the new one. i had to rev it and apply the braked to get into drive and crawl home!!!

please can someone let me know if this could all be related to the o2 sensors, or the air flow plug or anything else it could be.I am so thankful for you reading this long ass post and would greatly apreciate ur help.

Thankyou
Evan
1 - 6 of 6 Posts
Evan, you bought a car with problems. First of all you DO NOT have to unplug the MAF to read the diagnostic codes. Sounds like you have a bad MAF. You can buy one online at http://eactuning.com/mass-air-flow-sensor-e39-540i-from-09-98-p-418.html Best price I have been able to find. Try this first then see if you still need O2 sensors. If so your car 4 of them and they aren't cheap. Also check the whole vacuum system for leaks.

Good luck
Al.
I agree with the above--it COULD be bad O2 sensors (2 pre-CAT and 2 post-CAT, though generally you need only replace the pre-CATs), as the bad information they are sending to the CPU could cause intermittent stalling and overall poor performance, but I'd guess you may have other common problems, like a bad camshaft positions sensor (CPS) and possibly some other electrical issues. Maybe something more serious?--did you get it pre-inspected before purchasing?? As said above, there was no need to unplug anything with the MAF to run diagnostics so the seller is a liar who may be hiding something. I would bring it to someone with a diag tool to read any codes before you start throwing money at it. If the problems are just O2 sensors and CPS and such, then those are easy DIY jobs and the parts are around $100 or less for each sensor. Good luck!
thanks for your advice. i will have a look at how much this will cost. Do you know if it is a job i could do myself. I am moderately mechanically minded and have a few basic tools. I cold get the part tomorro from a main dealer, any idea how much that wil be?
thanks again for your help.

does anyone else have some advie?
ps other than this fault the cars in great condition it has 94000 on the clock and shows no rust so Im really hoping this problem doesnt develop anymore,
. the cars booked in for a diagnostic check on tuesday, im hopeful it will be the sensors and nothing more serious. the cars worth it though, and it doesnt suond like theres anyway around this problem without spending a bit of money, but i guess we dont buy bmw's without having to suffer a cheap weekend due to garage costs once in a blue moon!

im fairly sure now it is the sensors, the rear ones i think. will they both need to be changed and lastly could you tell me where they are located and how to fit them please

many thanks
If it's the MAF, it's only a matter of unclipping 4 clips so you can remove it, plugging the new one in and clipping it back in place. I am NOT mechanically inclined and I did it in 10 minutes with just a screwdriver to help unclip the clips. The prices from sources here in the U.S. won't help you much since you are in London, but I think it's safe to say the dealer will charge you 2 to 3 times what you'll pay for the same Bosche part in a BMW box than you can find just buying the Bosche part OR from Landrover. Landrover uses the exact same engine but sells the MAF for less than half of what BMW charges. As an example, BMW wanted about $450 U.S. for the part and $50 to install. I paid $158 for the Landrover MAF (same Bosche in a Landrover box) from an Internet dealer, but I've heard of Landrover dealerships selling the part for as low as $180 or so.

The pre-cat sensors (2 are needed) are about $180 each here if you buy them from the dealership, but if you buy the the same Bosche part from an auto parts dealer, they can be found for around $90 each here. I haven't installed them myself, but have heard it's as easy as unscrewing the old ones and screwing in the new ones.

I agree with the above poster that all you should need is the pre-cat sensors IF it's a sensor problem, as those are the ones that cause engine problems. The after-cat sensors just read what's coming out, so those wouldn't cause the issues you're having. I also think you're seller probably unplugged the sensor so that the engine would run without stalling (as that's one way to test if the MAF is going bad), so I'd start there.
thanks for your advice. i will have a look at how much this will cost. Do you know if it is a job i could do myself. I am moderately mechanically minded and have a few basic tools. I cold get the part tomorro from a main dealer, any idea how much that wil be?
thanks again for your help.

does anyone else have some advie?
ps other than this fault the cars in great condition it has 94000 on the clock and shows no rust so Im really hoping this problem doesnt develop anymore,
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