I have an intermittent check engine light, on my 1991 750iL. I have
the Bentley manual, that describes the connector location as beneath
the transmission. Is there any easier location to check the voltages
to the sensor heaters, and the sensor output?

The check engine light used to come on on the first hill a mile or so
from my house on the morning commute, but now it comes on immediately
upon startup, and sometimes goes out after highway driving.

I used the manual method of reading out stored engine codes (pumping
gas pedal 5 times right after turning on ignition, observing sequence
of flashing 'check engine light'), the output is 1444, which I believe
means everything OK.

I had the vehicle to a dealership before for the check engine light,
and they replaced one of the O2 sensors, upon picking up the car,
there was still a check engine light, but with different behavior, in
terms of when it turns on.

When I returned the car to the dealership, they claimed the check
engine light was due to a slipping transmission. I since had it
serviced, and noticed that the harsh down shifts when coasting 40-45
mph went away, I am unsure whether the slipping transmission engine
code was reset. But the check engine light never went away.

My gas mileage, is 13mpg (US), in a commute with 50% highway, 50%
local roads.

Are there conditions that cause check engine light to come on, without
storing a code?

Is there indeed a slipping transmission engine code for a 1991 M70, or
is the BMW dealership simply blabbering to cover incompetence?

Any other suggestions for how to troubleshoot this problem?

Jan Fure

<MGJonesMCMXCII (AT) gmail (DOT) com> wrote


<to the background blabbering>
The check engine light is emissions -related, not transmission problems. And
why the HELL didn't the dealer mechanics tell you that the first time? Bunch
of jack-offs! Am I wrong here... anyone?
My guess is you need both O2 sensors replaced and both ECUs reset. I say
both because the v12 has 2. That's right. Some would say disconnect the
battery for a few minutes and you're good to check if the light went out for
good. This would be a good time for a trans fluid and filter change, DIY, of
course. Can anyone back me up on this?

Bill in Omaha
'86 535i

"Bill" <wechorba (AT) yahoo (DOT) com> wrote in
news:kB6_h.287599$7g3.195246 (AT) newsfe14 (DOT) phx:

I would agree Bill. The first thing I would do is change the other
Oxygen sensor as well. You can reset the the ecu's in the way you
mentioned or by another proceedure layed out in the repair manual for
the car. I am about to change my sensors in my 850 because I am
experiencing the same thing as Jan at the moment. There is a fair bit of
coverage on this topic in the 8 series forum. Same engine with many of
the same problems.
Dave

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"D.Tugwood" <tugwood (AT) kos (DOT) net> wrote


Most of the info I culled from the WWW is somewhat model-interchangeable.
That's one reason I like BMW. I need to do a sunroof replacement soon due to
a PITA tiny rust spot. I'll be swapping in a glass section from... SAAB! I
found several articles and DIY, plus there's a yard here in Omaha with 5
donors.
Not a lot of folks know about the 2 ECUs for the v12s. Kudos to all those
folks who provided info that has helped me and those I've given the info to.
I guess my computer surfing time does pay off.

Bill in Omaha
'86 535i

Update:
shogun from a BMW forum gave me this useful reply:
http://www.bimmerboard.com/forums/posts/351877
and after stomping 6 times, I get a flash code for the left half of
the engine (DME2/cyls 7-12), from which I got code 2221, which means
oxygen sensor.

This one might be replaced under warranty, as this is the same sensor
as I paid BMW to replace for me last year.

Jan