Three wire oil pressure and two wire NTC oil temperature sensor shared ground

[Kaldek]

Hi Artur,

I just attemped to fit the following to my friend's car:

• Three wire oil pressure sensor
• Two wire NTC-1 oil temperature sensor

Both these sensors are the same sensors you sell on your website. The wiring for these sensors was:

• A6: +5v for oil pressure
• A4: GND for oil pressure *and* oil temperature
• A8: Signal for oil pressure
• A20: +5v pullup for oil temperature

With the sensors wired this way, the UTCOMP would not boot (black screen). It would only boot if we wired the oil temperature sensor ground wire to a dedicated ground wire.

I traced all other wires and there were no short circuits. Assuming that my wire tracing is correct, would there be a reason why the shared ground (using one of the DS18B20 grounds) between the oil pressure sensor and oil temperature sensor would cause the UTCOMP to fail to start?

[ArT]

Hi Kaldek,

This is good questions because... I have no answer
The reason may be in ground impedance - you have to high impedance on DS18B20 ground wire and - for example - pressure sensor add to it positive voltage (this sensor may need low impedance ground). It is better to connect solid wires for ground connections or connect directly to vehicle's ground. Please check also current consumption during startup. It is hard to diagnose these kind of issues on distance.

[Kaldek]

Thanks Artur,

I'm about to convert my car to using the same sensors as those that behaved oddly. With mine, I will wire both the oil pressure and oil temperature sensors to a chassis ground. I think your assessment of the ground impedance is probably correct. Nevertheless, I will post back here with the results of the change to my car when the parts have arrived.

[Kaldek]

Well I got my parts and fitted them. I wired both sensor grounds to the same ground as the UTCOMP and had no issues.

Looks like you were right!