Is it normal that the check engine light should come on when the diesel exhaust fluid warning appears? A few weeks ago, we got the Diesel Exhaust Fluid countdown procedure warning that the car would not start in xxx miles. I made the appt at BMW for an oil and exhaust fluid change.Just days before the appointment, the check engine light came on. While I assumed it was related to the exhaust fluid issue, I called BMW and asked that they check out the the check engine light. I was told that that would add another hours labor ($142) to check the code. I asked that they not check the code until after the service was complete as that service might cause the engine light to go out. I was told it did not go out, that they did the code diagnosis and the exhaust fluid tank was the problem, repair would be $1100.00. I said I'd have to think about that. When I picked it up I was told that the check engine light was out at the moment but would likely come back on. It hasn't lit back up after several hundred miles, all seems well. Should they have known that the check engine light was related to the diesel exhaust fluid? Might seasoned diagnosticians not have done the check engine code diagnosis?
Hard to say with out seeing the faults they saw. The e70 diesel is having issues with it's active SCR (selective catalyst reduction) tank level sensor having internal issues. They can not be replaced separate from the tank and it does cost quite a bit. They even had a recall on a select few of the E70's for this issue. I would ask BMW for assistance with that repair if you need to have it replaced.
As Charlson has said (and he probably knows better than I), the SCR is a complicated system. I had a recent similar experience with CELs, without a firm resolution, fortunately the CEL has gone away and not come back just like yours. I've had the mixing valve changed, the pre-cat mixer changed (both under recall and California emissions warranty fortunately), the DEF fluid checked, and other stuff. They were going to change one or both NOx sensors (very pricey items) but I held off and I seem to be good at the moment. However, I believe that the DEF transfer pump (in the tank assembly) is bad, so I have to add DEF 2500 miles or so to keep the active side filled - considering that the tank assembly on the sedan is like $1500 to replace I'll keep doing that. If you are in a CA emissions state, be sure to claim repairs under the 7/70 warranty.
I too have had these problems on my e90. My tank, exhaust metering injector and other part have been replaced. ( That and the EGR, 8 injectors and carbon scraping, etc. TG its CPO.) How old and how many miles? CPO? It could be under NCW ( new car warranty). I also agree with Floyd, CA emissions states are much more than CA and it could be covered under emissions warranty or another due to these problems Check around on the forum here and other places about the repair I know there was a bulletin or two.
