O2 sensor bank 2 continuous problem...

Jamiemac123

New member
Evening all,

I'm new to the z4 ownership, and am by no stretch a mechanic. A few weeks ago the emissions light (engine symbol) came up so took it to a garage. O2 sensor 2. Duly replaced. Got sensor 1 replaced at the same time both pre cat. (should have said its a 2.0 litre e85 2007 plate with 57k miles...)

600 miles later the light has reappeared and according to a friends obd2 scanner, it's the same fault... O2 sensor 2. This can't be the same problem? Car has been serviced including plugs, oil, filter etc etc. Anybody any ideas before I spend money hand over fist?

Please treat me like an idiot as I'm not a mechanic by any stretch...

Thanks in advance.

Jamie.
 
I'm no expert on the 2.0 so I could be way off the mark, however, the error code could suggest the sensor itself is faulty again (what does the error code read? for example running lean / rich?). Was it replaced with a new genuine OEM part or a EuroCarParts type generic sensor?

What would be more likely if you've just replaced it is that the sensor is getting a reading out of it's operating spec, if this happens a number of times it triggers the fault light, I believe it has allowances for 'one off' occasions and won't set off the warning light until it reaches a certain number of journeys with the fault.....(I could be wrong there but I believe that's how the S54 DME works in some respects.)

In that case, you're looking at something else causing the issue. For example, gasses escaping the manifold before it reaches the o2 sensor. I believe 2.0 do have cracked manifold issues? Or conversely, gasses/air entering the manifold that aren't expected by the DME.

Basically, more info on the code would be my first port of call. And an inspection of someone that knows of the manifold area to inspect for leaks, cracks or noises where air could be escaping / entering.
 
It seems to be a common 2.0 problem if you search the forum, it often shows fault code 29F4 / P0420 which relates to catalyst or others showing weak running. Often caused by fuel cap seal leaking, intake hose splits, micro cracks in the exhaust manifold, O2 sensors and or catalyst which can become damaged by incorrect running caused by something like the sensor or manifold problems. Some members live with intermittent lights on the 2.0 that cannot be fixed, others like poor old andysat gave up, sold and moved on (it's not andy's old car I hope :| )

First thing to do is get a decent code reader and research / post the codes as a starter.

andysat's problems
http://www.z4-forum.com/forum/viewtopic.php?t=60587

Edit - post crossed with andyBeech, great minds :)
 
Thanks for your offerings chaps. The code reader was a basic one and didn't actually give a code, just a written description of the fault. Annoying!

I'll take it to a garage as it does annoy me, although I don't think it has a detrimental effect on the car? If Andy's old car started HD07 then I've got it! A friend of mine runs a very good garage, so if my original repairer can't suss it out, which I hope he can as it's the same fault that he 'fixed', I'll take it there. Can't be bothered with the hassle seeing as I've only recently bought it :x

Hey ho, the joys of car ownership.
 
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