Testing Sensor Ground

I have a Link G4X Fury wired to a 1999 E36 M3 through a PNP adapter harness.

I attempted to make a subharness for an ethanol, oil temp/pressure and fuel pressure sensor by splicing into existing 5v, sensor ground, and 12v (for the ethanol sensor) lines on my OEM harness.

These sensors are all reading as expected, however I have concerns that I spliced into a chassis ground instead of sensor ground. When testing for continuity between the ground pins from my sensor connectors and the battery I am reading 45 ohms. I am not able to read any continuity when testing the connector ground pins against the shield ground or ground out from the A or B connectors at the ECU.

What lead my down this path is I am no longer getting a reading from my IAT or ECT sensors, they are both reading 4.96v with the sensors disconnected or connected which tells me I broke something during this process.

And last but not least, I am trying to test for continuity between the shield ground / ground out pins at the ECU and known sensor ground lines (MAF, TPS) and am not reading any ohms

I obviously messed something up, but feeling a bit lost on what to test to figure out my issue. Appreciate any help.

It does seem like you've broken the ground somewhere.

I'd probably make up a flying lead as a test ground, one end fixed to a known good ground and the other with a point, and go through the ground path using the point to pierce (if required) the ground, from the ground, and seeing where it is first working - the fault should lie between that point and the previous test point.

I found continuity between the TPS ground and the OEM ECU harness connector which must mean the issue lies somewhere between my PNP adapter harness and the ECU. I'll test the path as you suggested and see if I can find where the fault is.

As far as the subharness I made which is working, is it confirmed that its a chassis ground and not a sensor/ECU ground if there is continuity between the ground pins and battery negative?

Sorry, can't comment on the last, don't have the required experience, or I'm mis-understanding the question?

Just following up on my issue. I traced the path of my sensor grounds and I determined that I blew out two of the traces in my PNP adapter for the Temp Signal Ground and TPS Signal Ground. Most likely made a mistake with 12v when I was building out my subharness.

I worked around this issue by crimping the cam signal ground to the temp signal ground and wiring my subharness grounds off of that.

Double checked everything on my subharness, and all sensors are reading as expected again.