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I have an engine light on which is re settable with my code reader.

The code reader suggests it is an O2 sensor as these are over £100 each I would like to make sure it is in fact a sensor, as an air leak can cause a similar error

There could be a few things influencing the error as the first drive this year (6 months SORN) was with around 15 mikes worth of last years fuel now fuelled with new fuel but after 50 quick miles it returned while driving in town traffic

Poor connection at the plug half my axle stands are 125 miles away, so getting under the car is a challenge just now.

An air leak, how is a smoke test done to check this? And where are the likely places they leak. Have not found anything loose or split but vacuum leaks are hard to find.

Does anyone have the live data readings so I can check these against mine.
I have readings on bank 1 and bank 2 that match each other except one with is a little lower in value. But a reading from all of them.

Any other ideas?

PDJ wrote: ↑Sun Apr 04, 2021 3:32 pm I have an engine light on which is re settable with my code reader.

The code reader suggests it is an O2 sensor as these are over £100 each I would like to make sure it is in fact a sensor, as an air leak can cause a similar error

There could be a few things influencing the error as the first drive this year (6 months SORN) was with around 15 mikes worth of last years fuel now fuelled with new fuel but after 50 quick miles it returned while driving in town traffic

Poor connection at the plug half my axle stands are 125 miles away, so getting under the car is a challenge just now.

An air leak, how is a smoke test done to check this? And where are the likely places they leak. Have not found anything loose or split but vacuum leaks are hard to find.

Does anyone have the live data readings so I can check these against mine.
I have readings on bank 1 and bank 2 that match each other except one with is a little lower in value. But a reading from all of them.

Any other ideas?

I can probably dig out the reading later if I can find them from a while back. Is it post or pre cat sensors? If pre cat and never been replaced could be quite likely the sensors anyway as they get pretty nasty after a while. You don't have to buy BMW sensors to be honest, you can get much cheaper elsewhere which are exactly the same, can't remember the exact model number apart from they are Bosch (I made a thread about it a few years ago) but around £50-60 each I believe. I've replaced both pre and post sensors along the way and any error codes never came back after replacement. If you can get them from BMW for £100 each you'll be a lucky guy, more like £200+ each in my experience.

Air leaks are pretty uncommon but most obvious place would be the intake boot but it's made pretty solid so certainly not common. Only other thing is to check all the connections along the intake are fully on, oil return under the airbox, brake booster line from the boot, ICV line etc.

I leave mine for about 5 months over the winter and I've often had little issues that weren't there before putting it away. Strangely the TPS sensors are usual candidates for some reason. Just had mine out for the first time this year and all seems well this time luckily!

viewtopic.php?f=9&t=81469 The link to the original thread if you decide to buy new ones (these are for pre-cat rather than post cat though. TL:DR, Bosch part number you need is 0258017025 . Google it and you should get a fair few results. The length of the wire is the only difference to OE from BMW but makes no difference. Had these fitted to my car for the last 4 years with no issues.

As above doubt it’s an air leak. I had to change one of my pre sensors a couple of years ago. Cleared it a couple of times but soon came back.

These cars a susceptible to fuel change as well though, especially between 95 and 98 Ron switching. I’ve had to clear mine twice when 98 not been avsilable and a friends ///M when he put 98 in when normally running 95.

Does this look right price is less another 20%

Should be fine.
Other available on Ebay for cheaper, like here for example, only difference is the wire length is an extra 50mm which makes no odds.
https://www.ebay.co.uk/itm/173328593434 ... 1&mkcid=28


Up to you though, depends how much you want to save a few pennies! Worth looking about as per my previous post. Just make sure the wire length is at least 950mm (if it's pre cat, you haven't specified).

Though car parts for less was UK based

PDJ wrote: ↑Sun Apr 04, 2021 7:52 pm Though car parts for less was UK based

Soz yup correct, was thinking of the other one!

Looks like it is the one after the cat

After a chat with a friend who works for Audi Manchester I tried to find which one it is

The Audi ones have a transition phase when the heater turns off and then the heater does something else (too cleaver for me)

The engine was cold and during the warm up on the drive the light came on as I had the scanner plugged in getting some live data I then read the fault codes so it was re set and I went for a drive 10/15 miles and the light stayed off so it could be at the transition phase still means it needs a new one, but it looks like it is the one after the cat and these appear to be cheaper, I will change both after cat sensors as it will be easier to do two after the pain of getting it on 4 axle stands

pictures bellow probably not in the right order

PDJ wrote: ↑Sun Apr 04, 2021 8:07 pm Looks like it is the one after the cat

After a chat with a friend who works for Audi Manchester I tried to find which one it is

The Audi ones have a transition phase when the heater turns off and then the heater does something else (too cleaver for me)

The engine was cold and during the warm up on the drive the light came on as I had the scanner plugged in getting some live data I then read the fault codes so it was re set and I went for a drive 10/15 miles and the light stayed off so it could be at the transition phase still means it needs a new one, but it looks like it is the one after the cat and these appear to be cheaper, I will change both after cat sensors as it will be easier to do two after the pain of getting it on 4 axle stands

pictures bellow probably not in the right order
10DC8771-D05E-4DAC-AE5D-4EF05B5E307C.jpeg484DD991-161C-4BDC-AF48-C88420DB733F.jpegA18433CF-1531-4C43-BA5E-D61E2ED170D8.jpeg

Ah right, well after cat is quite easy to replace. I got some BMW ones off eBay for £37 each but got a bit lucky! Think I had the same error code or very similar, either way cleared and didn’t come back after replacing

PDJ wrote: ↑Sun Apr 04, 2021 8:07 pm I got some BMW ones off eBay for £37 each but got a bit lucky!

Any links thanks

Real OEM has two cable lengths so will aim to get one of each size

Auto Doc has some from £40 plus post from Germany looking for some UK based ones

Was about a year ago so doesn’t have any now. They were brought by mistake I believe so sold them for cheap.
Best I can suggest is use the part numbers from Realoem and put them in eBay see if anything comes up.

My friend had lambda errors for both his post cat sensors, I cleared the errors a few times and they always came back after an engine restart. I re-set his lambda adaptation on INPA and that sorted it.

Worth a try, but don't be too hopeful though. Replacing them isn't too much of a pain and you can buy Bosch ones for £55 or so on eBay. I replaced mine over 1.5yrs ago, and it's been fine.

When I view my O2 sensors in live data I use a graph format in my Engine Check Pro software on a laptop. I find the graph is easy to spot what they are doing, the Pre Cat sensor should be producing a regular wave form as its voltages rise and fall. The post cat sensor often looks quite static if things are ok, it will show some voltage changes when the engine is given some revs then stabalise when back to idle if things are ok.

Firstly - do check the wiring for these.
One of my clamps holding the cable was rusty/sharp edges, and had cut thru the cable coating - i.e. shortening the circuit. The O2 sensor itself was fine.
Restert - engine lamp gone, no error code.