Fault Codes A8 and 7B Associated Misfire?

[ChiefRider]

I put my new code reader to use today, and am puzzled- I should preface this by stating that I am a dinosaur, much happier working on anything made in the '70's or older...

I recently left my X5 with a shop while away for an extended time. I had asked for the expansion tank to be replaced (preventive maintenance) and for new plugs, in addition to some unrelated work. While there, they replaced upper and lower radiator hoses. The shop had authorization to thoroughly evaluate and we would discuss any other needs- nothing related here was found. I will note there was an occasional misfire when it went to the shop.

Now the misfire is worse- after warm up it can be quite evident above 3500 rpm. Additionally I now get a low coolant warning every so often. A check of the radiator shows the mechanical coolant indicator rise to its full height.

I have kept my use of the X5 to a minimum, and now that I have the NT710 code reader, the only motor electronics codes present are 7B, DME: Activation, map cooling and A8 DME: Thermostat, map cooling, mechanical, jammed open.

Thank you all for any insight!

[andrewwynn]

Both off those indicate a problem with the thermostat.

If the thermostat is stuck open, car will likely not get to closed loop which alone could cause your misfires.

Monitor temp with the scanner it will graph. It should quickly get to 90-95C and stay very close.

You can screen shot and email screen shots from the 710.

MAP shouldn't open tstat unless you hit the gas hard or put load like climb a hill.


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[X5chemist]

I chased a low coolant warning for months. Even swapped tanks and sensors. Traced it back to the sensor connection. One wire was broken at the connector. I repined and cleaned up the connection.

[ChiefRider]

Great information, thanks!

It has been awhile since I have replaced the thermostat- so will order one anyway. Will check the sensor connector as well.

Any supplier recommendations or should I stick with OEM?

[andrewwynn]

OEM it's best but i broke my OE thermostat and had to get whatever they had at O'Reilly. Wagner maybe is OE.

The heater inside fails and will give you the map error but when it fails open the car will never warm up to operating temps and the air fuel mix will be whacked once the engine sorta warms up but doesn't switch to using O₂ sensors to mix the fuel.


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[X5chemist]

Broken wire pics at the sensor connector.

https://xoutpost.com/bmw-sav-forums/...oogle_vignette