m3gusta Posted December 10, 2022 Report Share Posted December 10, 2022 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. 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. 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. Quote Link to comment Share on other sites More sharing options...
Adamw Posted December 10, 2022 Report Share Posted December 10, 2022 Give us a bit more info about the car and how it is wired. Your post suggests you have a wire-in ecu but then you mention an OEM harness also. Is it using an adaptor harness or has the loom been cut or something? Quote Link to comment Share on other sites More sharing options...
m3gusta Posted December 10, 2022 Author Report Share Posted December 10, 2022 It's a G4X Fury wired to the OEM harness of a 1999 BMW M3 using a PNP adapter harness. I am able to trace continuity from the sensor grounds on the OEM connectors to the OEM 52 pin connector. But I am not able to trace continuity from the OEM connector sensor grounds to the ECU Sensor Ground pins. With ignition on, there is continuity between the sensor ground pins on the G4X connectors and chassis ground / battery. Does this indicate a short from ECU sensor ground to chassis? I did confirm that with the subharness I made, I accidentally spliced into a chassis ground instead of sensor ground. Ironically, the sensors read as expected wired this way. I have since corrected this by splicing into an actual OEM sensor ground (which I have traced continuity to the OEM harness connector), but now all the sensors are reading 5v. Quote Link to comment Share on other sites More sharing options...
m3gusta Posted December 13, 2022 Author Report Share Posted December 13, 2022 Just following up on my issue - 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 making some kind of mistake 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 and TPS grounds off of that and so far we're good. Quote Link to comment Share on other sites More sharing options...
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