So glad I came across this post. The hose that goes from the coolant manifold to the heater valve (infamous #11) burst yesterday. Just put in a new one, topped off coolant and was frustrated that my gauge was in the red and KTEMP = -128c. Can confirm, battery nap fixed it for my 4.6is as well. I spent a little bit too much time today troubleshooting something that could have taken me 15 minutes :-)

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| E30 M3 | E34 M5 | E91 328xi | E53 X5 4.6is | E38 740i M-Sport |