Chasing a fault

[951driver]

Hope someone has expertise with this:
My M170 powers up normally and communicates over Ethernet with my PC on the bench. When I attach the car's harness, no Ethernet. I have confirmed (so far) the battery positive and negative wiring, along with the Ethernet to the port on the car and all of these are correct.
When I completed the harness I performed a point to point continuity check for all wires and terminals without faults.
Despite that, it would seem that something else is blocking the unit from powering on. Does anyone have insight to where to look first or what method works best for troubleshooting this?

Appreciate any help you can send my way!

J Allen

[David Ferguson]

Double-check your power / ground. Compare to your bench harness.

It's got to be the wiring. Standard trouble-shooting techniques. Remove all devices attached to the ECU harness except power and ethernet. Does it power up?

Check for shorts in harness by checking resistance between all pins and Battery Negative, and all pins and Battery Positive

Still nothing, start removing pins from the connector, you'll find the problem quickest if you remove/re-install half at a time.

Can you put an oscilloscope on the power to the ECU and see what happens to the voltage? Can you measure the current and see what's happening. If it's powered by a PDM, perhaps your settings are tripping a current limit.

[951driver]

Thanks for your thoughts, David.
I’ll try suggestions and something will pop up!

[951driver]

Mystery solved. One of the Ethernet sockets wasn't fully seated in the connector. I suppose it was adequate when a pin was inserted, perhaps just a little further than the pins on the connector, for a continuity test, but not to allow the Ethernet connection. I noticed it because the socket wasn't as visible in the connector, exposed it and seated it with the tool which then rewarded me with the "click."
Thanks for your comments David, and I guess I need two pulls on every seated wire!

[David Ferguson]

Excellent. Thanks for following up with the root cause.