[Ulle]

"- A0 and A1 each with an identical resistance of 1.5k to 5V of arduino"
Then its parallel with the bias, I thought it should go to ground.

Please keep in mind that the speeduino is not connectet. So i use the direct 0-5V inputs of the arduino.

But you helped me to find a mistake I did. For constant voltage i have to make a voltage dividor between 5V and GND!!!
I made two voltage dividors for each temperature channel and now all seems OK.

I'm sorry for the confusion

Now both channels react identical.

That means the error only arises when the speeduino is connected.

[Ulle]

It looks like I found something out about IC4. Like I said before, the Speeduino seems to measure properly without it. So it couldn't have had anything to do with wrong settings. The problem also does not seem to be due to the soldering of the circuit board as the following resistances are OK based on the circuit diagram.

Pin 19 -> A0
Pin 19 -> A1
Pin 20 -> A0
Pin 20 -> A1
Pin 19 -> Pin 20
A0 -> A1
Pin 19 -> GND
Pin 19 -> 5V
Pin 20 -> GND
Pin 20 -> 5V
A0 -> GND
A1 -> 5V

As I mentioned, when IC4 is inserted, the signals from the VR board, ECT and IAT interfere with each other. It was really hard to read but the labeling says it is a IXYS ixdn602pi what means it is a dual high-speed gate driver, not a diode array

It was in the kit from diy-efi.co.uk labeled "IC4 - SP721APP" what means he accidentally sent me three drivers instead of two. Due to the almost unrecognizable labeling on the IC, my lack of experience in ICs and microelectronics, this was very difficult for me and it took me much time to find out.

I hope the problem is solved with a SP721. I will give feedback.

[Ulle]

UPDATE

Problem solved!

Today the new IC arrived. Everything works as it should now. Normally I check all the values of the components before I solder them. But with a complete kit and a single-packed and labeled IC, I haven't come up with the idea it might be wrong. You can't change anything about it now, mistakes can happen.

[PSIG]

I summarize:
…
- A0 and A1 each with an identical resistance of 1.5k to 5V of arduino

I just saw this old thread randomly... Anyway, NO, not 5V. The test is 3.3V on the Mega board jumped to the A0 and A1 Mega pins. With the GM CLT and IAT calibration, the predictable calculated result reading 3.3V on those pins will be 10° to 15°.