OneSeventy 1 Report post Posted August 16, 2012 Hey everyone, the other day I had my pre-cat oxygen sensor fixed up and it was fine for a day and then my check engine light came on again. Scanned again and this time it's the oxygen sensor after the cat. Is this strange behaviour or just bad luck? I have to admit I don't know much about how all of this works so any advice would be appreciated. My car is a manual 2001 E46 318i sedan if that helps in any way. Quote Share this post Link to post Share on other sites
hotwire 352 Report post Posted August 17, 2012 Was the first one faulty? Who checked the car - did they know what they were doing? 02 sensors (& other sensors) can throw fault codes when they fall outside their operating parameters due to outside influences - vacuum leaks etc. Quote Share this post Link to post Share on other sites
OneSeventy 1 Report post Posted August 17, 2012 I see. I took it to a place that specialises in German cars, BMWs in particular. So if both oxygen sensors were showing up within a few days of each other, you're saying it is *likely* to be a vacuum leak, or just that there is a chance it is? How would I know? I should mention my car has been idling a bit low recently and it often shudders a bit when taking off in first gear while cold. Does this help with a diagnosis? Quote Share this post Link to post Share on other sites
*Glenn* 854 Report post Posted August 17, 2012 It's very unlikely that both would fail. As Grant said, it's possibly something else that has triggered the fault code because the sensor is outside of it's operating range due to over or under fueling. What was the actual fault code ? word for word. Did they store or save the fault code ? Quote Share this post Link to post Share on other sites
OneSeventy 1 Report post Posted August 17, 2012 Unfortunately not. Damn, I'm not good at this stuff! The lights back on though and I'm going back in. I'll see if I can get the code and exact wording and report back. Thanks for your help so far. Quote Share this post Link to post Share on other sites
*Glenn* 854 Report post Posted August 17, 2012 Give me a call Monday morning... any time after 7.00 am....(09) 2722546 Quote Share this post Link to post Share on other sites
OneSeventy 1 Report post Posted August 18, 2012 I'll give you a call Monday Glenn but thought I would post up today's findings: Took the car back in but I had to leave it with them and then when I picked it up, they were closed so I didn't get to grab the codes unfortunately. The guy said he replaced a spark plug for me as one cylinder was misfiring slightly, he checked the hoses and stuff and found nothing, and he said something about resetting all the oxygen sensors (?) so that the car now idles better, as he agreed it was idling a bit low. He didn't charge me for any of this. Went for a drive a few minutes ago and the check engine light went out after ignition as normal, but a few hundred metres down the road, it was back on. I'm stumped. The car drives the best it ever has while I've had it, it has just had a full service, and professional "BMW specialist" mechanics can't work what's wrong with it! Quote Share this post Link to post Share on other sites
OneSeventy 1 Report post Posted August 18, 2012 Been thinking about this and I think the main thing that pisses me off about both my faults that are showing codes (airbag light is on too) is that they both don't come on straight away. Airbag light once took over a week to come back on and this oxygen sensor code issue seems to either come on when cold or just take a few hours. This makes it painful to fix because the mechanic can't know for sure if they've fixed the issue. Quote Share this post Link to post Share on other sites
hotwire 352 Report post Posted August 19, 2012 Been thinking about this and I think the main thing that pisses me off about both my faults that are showing codes (airbag light is on too) is that they both don't come on straight away. Airbag light once took over a week to come back on and this oxygen sensor code issue seems to either come on when cold or just take a few hours. This makes it painful to fix because the mechanic can't know for sure if they've fixed the issue. Was the airbag fault determined originally? Fault codes are stored in the applicable modules & can easily be recovered - even with a non current fault. Quote Share this post Link to post Share on other sites
OneSeventy 1 Report post Posted August 19, 2012 Was the airbag fault determined originally? Fault codes are stored in the applicable modules & can easily be recovered - even with a non current fault. Glenn has had a look at the airbag fault. He tried to fix it but it didn't work and so we found it would be an expensive process to properly determine what is causing the fault and left it for now. I can't remember the exact fault but I am sure Glenn can say... It's something like "Driver Airbag stage 1". I'm more annoyed about this 'check engine light' that's popping up at the moment than the airbag fault. Quote Share this post Link to post Share on other sites
OneSeventy 1 Report post Posted August 19, 2012 Went down to the garage again and he cleaned out the idle control valve just in case it was that. He said there was some carbon in there but not a lot, so unlikely to be the cause. He also showed me how to disconnect the air mass sensor which we are going to trial to see if it fixes the rough idle problem. It sounded like he was saying that if the car drives better without it, we can assume that it is faulty. Strange thing is that both he and I agree that the air mass sensor looks brand new, as if replaced not long before I got it, so I don't know if this will work. Quote Share this post Link to post Share on other sites
OneSeventy 1 Report post Posted August 26, 2012 Been sick for a week so I had barely driven the car until yesterday. But before I did, I opened the hood and disconnected the air mass sensor. I started it up and it shuddered and shook for a good minute – I even tried to still drive away a few times but both times the revs faded and the car stalled before I could move. I decided to give up on that test so I plugged the air mass sensor back in and surprise surprise, the light has gone away (for now). Does this confirm the air mass sensor is the fault? Quote Share this post Link to post Share on other sites
Jono51 58 Report post Posted August 26, 2012 (edited) Been sick for a week so I had barely driven the car until yesterday. But before I did, I opened the hood and disconnected the air mass sensor. I started it up and it shuddered and shook for a good minute – I even tried to still drive away a few times but both times the revs faded and the car stalled before I could move. I decided to give up on that test so I plugged the air mass sensor back in and surprise surprise, the light has gone away (for now). Does this confirm the air mass sensor is the fault? Glenn has offered to look at it for you previously , best that you call him by unplugging items you are adding new faults, that will show in a scan and can be misleading Edited August 26, 2012 by JKSE Quote Share this post Link to post Share on other sites
OneSeventy 1 Report post Posted August 27, 2012 (edited) Glenn has offered to look at it for you previously , best that you call him by unplugging items you are adding new faults, that will show in a scan and can be misleading Glenn offered to talk on the phone and we did a week ago. As I said, I unplugged it but have plugged it back in now. For some reason that's caused the light to turn off. Edited August 27, 2012 by OneSeventy Quote Share this post Link to post Share on other sites
Jono51 58 Report post Posted August 27, 2012 Glenn offered to talk on the phone and we did a week ago. As I said, I unplugged it but have plugged it back in now. For some reason that's caused the light to turn off. been reading through the past posts, I see you mentioned that only one spark plug was replaced I find this odd, these are usually replaced as a set, as a rule of thumb Also just resetting the o2 sensors odd as well, this hasn't been diagnosed properly at all, AFM, Cyclone valve, intake profile gaskets , vacuum lines, blocked fuel filter its all guessing give Glenn a call, book it in get it scannned and diagnosed properly, as over the net is guess work Quote Share this post Link to post Share on other sites
