Oil pressure changing with battery voltage

[gtbtdi]

Hi
I have a VDO oil pressure sensor connected only to AdcVcc1. I calibrated sensor using excel sheet on tutorials topic.
Utcomp shows bit low readings compared to resistance value measured with multimeter, that can be fixed changing calibration values. But what I have not solved is pressure values changing with battery voltage.
Example: utcomp showing voltage 14,2V and oil pressure 1,4bar Then I switch on heated seats and driving lights, voltage drops to 13,6V and oil pressure goes to 0,1bar, engine RPM stays the same in both cases.
Sensor model and values

[ArT]

How did you connected the sensor? It has 2 pins, 1 pin should be connected ONLY to UTCOMP, to pin AdcVcc1, and 2nd pin should be connected to UTCOMP ground (black wire). If connections are correct, please measure voltage between sensor's pads when you have on accu 14,2V and when you have on accu 13,6V. What's the difference?

[gtbtdi]

Utcomp is connected to the sensor pin, there is nothing else connected to the same sensor.
Second pin (no connection) is for warning contact and ground is connected through engine block.

[gtbtdi]

I noticed that there was some voltage between engine block and negative battery terminal, that voltage changed with the load.
Alternator is the reason for this voltage change, I guess resistance in ground wiring allow small rise in the engine blocks voltage level.
I managed to alleviate problem by cleaning engine ground wire and adding another thick ground wire directly to the oil filter base.
Now there is only 0,2 bar difference in the utcomp pressure display between min and max load.

Note for future users, its better to use sensor(s) with separate ground wire