I would say you are in uncharted territory. Even the guys that originally did the buffer mod never chased the LED or couldn't. :dunno:

Yes, I think that thread kinda ended in confusion. I did read somewhere that the DME will use intake temp if it thinks coolant temp fails so there could be other substituting going on as well. One nice thing is that I did find out while I was trying to get the light to come on is that there is an engine cooling strategy based on the lower hose temp(I am running without the mechanical fan) which cuts the aux fan in at about 185-190 F so I might not need to build the fan controller I was planning.

Here is a crazy thing since talking about cooling strategy: when wife's car overheated due to loss of coolant, the aux fan didn't come on even at 210-220. I wasn't there when the needle was pegged at 260!

The car set an SES code for shorted coolant temp sensor it thought the reading was erroneous it seems. Maybe because the ect was so much hotter than the oil temp or something?

Anyhow I was concerned the aux fan was broken but I was able to turn it on manually with the foxwell. Just was very confused that the aux fan wasn't running. Maybe the clue is above that the computer uses outlet temp to decide when to kick in the aux fan.

I'd jump in and offer some help but I can't even find any info. on a temp light at all - not a good start! ;)

What temp light? Where? :dunno:

As complete aside, the temp sender on my bike (BMW) uses a dual temp sender from BMWs parts bins - but it only uses one of the sensors. Possibly the same sender...

@wpoll, I think the diesels are completely different for that.
@andrewwynn Yes, it seems the aux fan only comes on with the coolant hose sensor.
The sensor would be almost shorted at that high of a temp.

When I first checked into it I had the DME side (voltage) pulled down all the way to (simulate) 142 C and neither fan or coolant light came on, when I snipped the gauge side though the light did come on. I think it only will come on with DME temp if it thinks the gauge side has failed so that is what I am going to check into next.

Hey 80stech, was aware that the diesel is different so I've been searching M54/M62/N62 variants but so far I've not seen anything about a temp light... anywhere.

Clearly there is one on your car (you activated it) but are these temp lights rare or something?

What a nerve wreck lol. Well, I did this change to mine, I run the n62 that runs WAY hotter than the m54. I guess now I see why BMW decide to code like this from the beginning it kinda works for both m54 and n62. Here is what I did I am going to test it in a few, and will update the post if I need to do any change. Do you think there is a better way to code it? Or it's good?

Honestly that is entirely up to you. That should work just fine but a 25C buffer is still kind of numb. In normal driving how often did it get below 90C? Mine only dropped out of my buffer when I gave it substantial load or throttle demand. Maybe a 90C-110C buffer? The rest of it looks good but maybe move the high side up an additional 5C? 120C and 125C for red zone since you run at 110C already? :dunno:

I set the buffer like that because that's what the engine runs (check post#41) but what you say makes sense the engine so far (winter time) normally runs at 105C +-3C. I will change the red zone temperatures.

@wpoll It's the red portion of the gauge that lights up, If you have it. It will come on with the bulb test when you first start the vehicle or if you activate the dash test or reset.

@Emory The guage will not stay exactly in the center for the whole range of the center "buffer" portion so it's not really as wide as it looks. It's easy enough to change when you get it figured out so doesn't hurt to try a few things! :)