Faulty 02 Sensors - TECHNICAL UPDATE!! (pg.5)

thats the back of of the engine block, the wires are clipped to the manifold cover and also the gearbox casing.

these are sensitive items so its always good to have a check how they are routed and if they are tightly clipped in place, they are not cheap to replace and a royal pain in the ass to do tbh... the pre-cat units don't seem to bad looking at that, post cat... exhaust off job.
 
Beedub said:
thats the back of of the engine block, the wires are clipped to the manifold cover and also the gearbox casing.

these are sensitive items so its always good to have a check how they are routed and if they are tightly clipped in place, they are not cheap to replace and a royal pain in the ass to do tbh... the pre-cat units don't seem to bad looking at that, post cat... exhaust off job.
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I think this is what had happened to mine. The cable had rubbed against the engine block, worn through and knackered the sensor.
 
Beedub said:
thats the back of of the engine block, the wires are clipped to the manifold cover and also the gearbox casing.

these are sensitive items so its always good to have a check how they are routed and if they are tightly clipped in place, they are not cheap to replace and a royal pain in the ass to do tbh... the pre-cat units don't seem to bad looking at that, post cat... exhaust off job.
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Funny it's almost the opposite of what BMW have said. I've paid £425 for the pre cat (as it's more labour intensive) and £246 for the post cat.
 
don't see why pre cat is more labour intensive, the can be done very easily by removing the reinforcement plate. the post cat units are tucked ONtop od the cats and sit right up against the body basically , to get at them needs the exhaust dropping... hell with a long enough extension and wobble end you can get to the pre cats from up top.. take and look and you'll see what i mean.
 
OK, so an update from BMW.

Good news and not so god news.

Good news is - No air leaks, so no new exhaust manifold needed *phew*

Bad news, they've changed both 02 sensors on bank 2, took it for a road test and EEV light came back on, plugged it in and now the pre-cat sensor on bank 1 is showing as a fault.

So, it's got to that point where I have lost all confidence in BMW actually diagnosing the root cause of the issue and they are merely changing parts out in a "process of elimination".

Appealing to the technically minded on here, does anybody have any idea why B1S1 02 sensor would now be showing a fault that wasn't previously there?
 
The ratio of O2 between the two sensors causes changes in the fueling rates. One failed sensor causes the long term ratio to change and when the new sensor is fitted it again causes a similar ratio change.

The reset of faults and a period of running then another reset should eliminate the "delta" due to the first sensor failure. Continuous changing of O2 sensors will just continue to cascade errors being reported.

Change once then check emissions, run for a period (the error will reappear) then just a reset and the error should not reappear.

The initial fueling rate error is cleared at the time the sensor is replaced but the long term fueling ratio takes a period and several cycles to become "normal" then a subsequent reset should be all that's needed.

:D
 
Erk - sorry to hear it's not solved.

Where do BMW stand with regards to you having now paid them ~£X for ... nothing?

I'd defintely consider phoning Phil @ CPCPE, or Stuart @ ML and asking if they have any thoughts. They may actually have some experience of this, and the works done by BMW so far may be enough to help them to the right answer.

What is BMW's next idea?
 
So seeing Nelly's post... Presumably the EEV light is activated once the delta of two sensor readings breaches some sort of limit, rather than whether there is a fault or not? (caused by the change of sensors, potentially now both being accurate?)

Ergo - A bit of driving, plus a reset, then a bit of driving.. may result in no more EEV and problem solved?
 
Nelly Welly said:
The ratio of O2 between the two sensors causes changes in the fueling rates. One failed sensor causes the long term ratio to change and when the new sensor is fitted it again causes a similar ratio change.

The reset of faults and a period of running then another reset should eliminate the "delta" due to the first sensor failure. Continuous changing of O2 sensors will just continue to cascade errors being reported.

Change once then check emissions, run for a period (the error will reappear) then just a reset and the error should not reappear.

The initial fueling rate error is cleared at the time the sensor is replaced but the long term fueling ratio takes a period and several cycles to become "normal" then a subsequent reset should be all that's needed.

:D
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Thanks Nelly, that seems logical to me.

BMW's current plan is to change the 3rd (b1S1) O2 sensor to rectify. I've just phoned to relay this information, asked them to clear the fault again and take for another road-test and to give me call when they have done that.

I'm tempted to pick the car up and run it over the weekend. Reset the fault code again (should it re-appear on Monday) and take it from there.

To be fair to BMW they are being very good from a customer service perspective and are matching prices for changing the O2 sensors that I've had quoted from some Indys. They have also agreed not to charge for any ongoing diagnostic work and are discounting their labour rates for any repair works by 20%.
 
The dealer should reset the fueling adaptions after changing the o2 sensor. That will fix the delta issue unless it is genuine fault.

The adaptions take a while to update so a second short road test might not bring the delta back into line.

Edit: i see Nelly has already covered this :)
 
I think its like an ECU reset - as in, clear all learned fuel information/driving style info. Isn't there a manual process you can follow (akin to starting the car, stopping the car, turning the key to position 2 and then doing a headstand in the passengers seat whilst turning aircon to 28% .. or similar)..?

I think its used for resetting learned throttle response and other stuff too right?

Not sure if the fault code reset covers this.
 
jimmybell said:
I think its like an ECU reset - as in, clear all learned fuel information/driving style info. Isn't there a manual process you can follow (akin to starting the car, stopping the car, turning the key to position 2 and then doing a headstand in the passengers seat whilst turning aircon to 28% .. or similar)..?

I think its used for resetting learned throttle response and other stuff too right?

Not sure if the fault code reset covers this.
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I think somebody mentioned once that disconnecting the battery for 30 minutes would do this.
 
Live data on the dealer tool should determine what lambda's are working correctly and what aren't..The Baud rate can be seen and graphed/mapped..

Fault codes dont tell the whole story im afraid.
 
Right so a little update.

The car is back from BMW and tucked up safely. The light is off and the car is driving fantastically well.

I'm going to monitor over the next week or so before announcing success.

BMW were very good to me. 3 sensors changed ( both pre cat and bank 2 post cat), they didn't charge any labour for the last 2 days work which included the 3rd sensor and all air leak diagnostics, nor did they charge for the courtesy car.

The total cost was £954 in the end, a princely sum but not unreasonable considering the three sensors are £600 and diagnostic £90.

I'll still be using ML for all servicing and preventative maintenance....or any scarier symptoms, but on the whole I think Vines Guildford did a decent job (in the end)
 
Beedub said:
f**k me.... these cars... 900 quid to change 3 sensors..... madness.....
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Yeh I know, not sure how I could have avoided this, but highlights the importance of preventative maintenance.

insp. 2 in Jan for me, so will be getting lots of things done/ checked at the same time.
 
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