Hello
I would like to program my halogen heater (monitored with LEDs) to have an approximately 5 °C higher activation temperature threshold. However, VAGCOM does not offer an adaptation channel for this.
So, I had to resort to the old method of manipulating the sensor signal again - here, with the intake air temperature sensor, which also determines the outside temperature for the halogen heater.
For example, the measured temperature can be reduced by connecting a resistor in series with the sensor.
To make the TDI-EDC sensors appear to read 0°C instead of 5°C, one would need to connect approximately 1.2 kOhm in series with the sensor.
However, in the upper measurement range, for example, real air temperatures of 50°C would appear to be approximately 25°C. I didn't want to deal with such consequences, especially since there would be no gain in performance or any other benefit.
In the motor computer, I found 750 Ohm internal SMD pull-up resistors on a common 5 Volt (?) wire connected to pins 14, 63, and 64 (motor, fuel, and intake air temperature inputs).
A rough calculation using the target values for different temperatures showed that changing the pull-up resistor shifted the apparent temperature throughout the measurement range by a fixed degree. Reducing it by 5° would result in 630 instead of 750 ohms.
Therefore, I replaced the 750-ohm pull-up resistor for the air flow sensor with a small 644-ohm resistor, which I salvaged from an old, defective L-Jetronic STG (it's good to reuse things like that
).
A subsequent temperature comparison of all sensors via VAGCOM with a cooled engine showed the following:
Water + 2.7 °C, Diesel + 4.5 °C, Intake Air - 1.8 °C
Therefore, the intake air was 5.4 °C below the average of the other sensors. And the same 5° error in the upper measurement range does not seem critical to me.
Shortly after the engine started, my tractor also switched on the heater glow plugs, which it usually did not do under such "mild" conditions.
For anyone who wants to install the part with the part number 028 906 201 GH on the engine computer:
The specific pull-up resistor with the purple-green-black color code is located in the left front area of the PCB, as seen from the connector side.
If you follow the trace from pin 64 (the last row of holes, starting from 68 and counting backwards), you will find it after a few centimeters.
The effects of using the next common pull-up resistor values instead of 644 Ohms:
680 Ohms reduce the apparent temperature by about 3 °C, 560 Ohms by about 8 °C.
3.9 kOhm in parallel with the 750 kOhm pull-up resistor reduces the apparent temperature by about 5 °C.
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, sondern erst unter ca. 1 °C. Dann wurde er (wie allgemein bekannt) schneller warm als z.B. bei 3°C.
