Hopefully the attachment worked... the N62 engine operates from 85C-110C. So V8 guys need to modify the new hex code accordingly.

I have one and it has a blue background light.

I'm going to try and do something with an Arduino in the E-box over the holidays. All the necessary wires are there including access to the dash warning light and looks like won't be hard. Would anyone have access to the voltage to temp conversion numbers or logarithm ?

NTCs are typically linear over the useful range. Take a couple Ω readings when it's not connected with some known temps easy math from there. I would love to have the warning light come on at 115C

I'm not sure what pull-up the factory DME uses but here is one of my calibration tables using a 1K ohm pull-up to 5V. It is a Bosch 023 temp sensor and should be roughly the same as what BMW uses. :dunno:

Yes, I was thinking of just tracking the temp with inpa and taking some voltage points and going from there. The beauty with the arduino is that it makes possible all kinds of flexibility including linearization, turning on the light at what ever temp, even variable brightness to temp, flashing etc. adding audible warning, even engine shut down if parked and self diagnostic features!

Thanks OB! :) that could prove to be very useful!

If it is indeed a 1K pullup to 5V, I calculated the voltage low and high at .370V to 4.765V. Keep in mind the sensor is non-linear and I can get you all the voltage conversions if needed. I just used an online voltage divider calculator.

V_{out} = V_{in}*\frac{R_{2}}{R_{1}+R_{2}}

Frustrating to know BMW thought to sound a gong when the outside ambient temp hits 37F but didn't bother to sound the gong on something so critical like a melting engine... :(

Nice that they have a separate sensor for the light vs. the gauge needle. Good redundancy.

I'd be concerned about some other system using that sensor before modifying it.

But if it's independent and you just want to change the temp the light comes on at, wouldn't it be most easily done with a resistor?

For example, looking at overboost's post #45, if those numbers were correct for our cars (I know they are not confirmed, but as an example, if they were correct ...), and if we found that the light came on at 120*C and we wanted it on at 110*C (again, just taking easy numbers here for the example) ...

The light would currently come on when resistance dropped below 115 Ohms (at 120*C). We want it to come on at 110*C (when the actual resistance is 140 Ohms). So we want to add a resistor that makes 140 Ohms look like 115 Ohms. To do that, you wire one in parallel with a resistance = (140 * 115) / (140-115) = 644 Ohms, in this example.

Would that help?

I have not even done the firmware parameter re-coding yet (partly because I don't even have an INPA or anything beyond a standard OBD2 reader), but I think the warning light would be at least as important as the needle.