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Dado 540 10-19-2010 02:20 AM

CEL on...temp gauge all the way on engine temp -128C
Driving enjoying the 540i and the "check engine" light comes on. 10 minutes after i notice the temperature gauge is all the way to the right on the "red".

I pull over immediately and check the digital engine temperature read out and it says -128C (yes negative 128)

No sign of any coolant issues. No smoke. Nada.

After fiddling around and just letting it cool off, turned the car on a few times but the needle rockets to the red zone. I figure its gotta be a malfunction with the some sensor, i started her up and drove off. Check engine light remained on, however the temperature gauge went back to slightly below the half way mark while i was driving. Engine temperature digital output was 70C and increasing slowly making its way to 85. By that time i was home and the needle was on the center.

Gonna inspect the coolant level once its cool enough, even tho i did not get "low coolant level" message. Definitely gonna have to get her scanned.

Anyone with ideas of a possible culprit(s)?

MLue1 10-19-2010 10:21 AM

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Davor, -128 sounds like a sensor and/or connection. The engine should be fine if there is no leak the Thermostat will still do its job.
Check the Double Temp Sensor, #9 in the diagram or the connector that is what sends the temp signals to the computer.

Dado 540 10-19-2010 01:30 PM

Hey mark, thanks for the quick reply. I inspected the sensor you mentioned and it seems to be in place. I drove the car today the temperature is fine, however cel is still on.

I guess the scan will tell all.

Edit: operating temp is 78C needle at half way mark

MLue1 10-20-2010 12:06 AM

It's probably in what they call "Engine Fail Safe Mode", I hope they find something, there is nothing like having an intermitent problem like that*thmbsdwn*.

Dado 540 10-20-2010 02:12 AM

Ok so had her scanned today (luckly my co-worker had an ODB II scanner in his car).

Code is P0116 - Engine coolant temperature circuit range/performance

Did a search online and ripped through the bentley manual and found quite a few people with the same issue.

Initaly the suspect is the coolant temperature sensor, however some have replaced it and problem was still present. Only after the thermostat was changed everything cleared up.

Here is one of the links:

Ive had an issue with the thermostat before where one of the two wires going into the sensor was disconnected. I havent had a chance to check, but im assuming it must have gotten moved again.

Since this is an electronic thermostat (integral electric heater in the thermostat), its most likely in limp mode (running mechanincal action) just as a failsafe not to overheat the engine. This would explain my current temperature of 74C.

Hopefuly some of you find this info useful. Cheers

Mark thank you as usual.

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