850i Cluster Temp Sensor Erratic

[DeltaSix]

I'm having a recurring issue where, when the engine has reached temperature, the cluster temp sensor will fluctuate between cold and mid-temp. It never goes to the hot side, always cold side. It can sometimes dip to a 1/4 temp then back to mid, or dip to almost cold an pop back up, it can dip slow or fast and return to mid slow or fast. Although subjective, this seems more prevalent on hotter days after a long period driving. I have already replaced the cluster coolant sensor once at the back of the engine. I don't mind having to do it again, but it would be nice to understand why it is happening.

Anyone have any thoughts on how to diagnose this? Perhaps a wiring issue?

[rjjablo]

Check coolant level.Do you know if it has a thermostat?

[DeltaSix]

Coolant level checks out OK. The termostat is an 85 degree unit, installed with the spring hot side and the breather hole at the top.

[DeltaSix]

Looking at the EKM diagrams in the ETK, the Coolant temp sensor goes to the EKM and then to the cluster via the datalink. As I mentioned above, the gauge never reads more than midway, it just fluctuates between cold and mid-temp apparently randomly. But never more than mid-temp.

If the coolant temp sensor is an NTP, wouldn't that mean that at the higher the voltage drop, the cooler the reading. The lower the voltage drop the hotter the reading?

I recall reading at some point in the past that either the cluster or the EKM buffer the coolant temp sensor, and the mid-temp location is actually a range from ~80-110C.

What I'm getting at here, is perhaps there is a bad solder joint in the EKM or bad wiring from the sensor to the EKM, and it's causing the voltage to drop to 0. The EKM is buffering/averaging this voltage reading and slowly/quickly moving the needle depending on the occurrences of 0s in the average calculation. And by extension, the occurrences of the correct Voltage reading causing it to return to the mid-point when the circuit reconnects.

Are these reasonable assumptions?

[Timm]

Yes, it could be the sensor itself, these do fizzle out....

[DeltaSix]

Two sensors in a row have exhibited this behaviour. I might just replace it again to see if it resolves the issue


¯\_(ツ)_/¯


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