Active Shutter Grille U510

Hi everyone, this is my first post. I have a 2018 Silverado High Country 5.3 that threw the code U1510 2 weeks ago. I pulled it up with my basic code reader. I can verify that my active grille shutters are locked open & will not close. I am able to verify 12V. power (violet blue)  and lin bus (green violet) and ground at the shutter connector by the left headlight by back probing with my multimeter.. I don't have a scope so I cant properly measure the lin bus wire but with my multimeter it reads about 1 volt less than the 12 volt wire & it fluctuates up & down between 10 & 11 volts. I replaced the grille shutter with an aftermarket version (Dorman) yes I know me bad! New new shutter is also unresponsive and got the same readings from it. My retired mechanic friend put his Snap On  scanner on my truck & could not get it to open or close the shutters on the original or the aftermarket. I am reluctant to purchase an OEM shutter until I am sure the problem does not lie within the wiring. Could it be that the aftermarket shutter is not recognized by the PCM? Any advice is appreciated.
 

I am able to verify 12V. power (violet blue)  and lin bus (green violet) and ground at the shutter connector by the left headlight by back probing with my multimeter.. I don't have a scope so I cant properly measure the lin bus wire but with my multimeter it reads about 1 volt less than the 12 volt wire & it fluctuates up & down between 10 & 11 volts.

Hey Glenbo. Your testing sounds solid to me. The scope waveform would be nice, sure, but I don't think it's needed.

But, if you're looking for that 110% confidence before going for an OEM part, there's a couple suggestions I can make. One would be to load test the shutter power and ground circuits with a test light. GM actually recommends this in the U15XX service information. Probably unnecessary - your backprobed voltage readings were fine - but still another test you can do.

Another would be to disconnect the shutter and recheck for voltage on the LIN bus wire. You should still get 11-12ish volts. Disconnecting the shutter ensures that the voltage you're seeing is coming from the ECM, and not from the shutter. That matters because, if there were an open in the LIN wire between the shutter and the ECM, you wouldn't be able to tell with the backprobe test alone. Disconnecting the shutter will verify the circuit integrity.

GM PIT5698 has some excellent tips for LIN bus testing, if you're interested in doing some more reading:

 

From PIT5698:

 

Could it be that the aftermarket shutter is not recognized by the PCM?

That'd be my suspicion. Dorman (and the rest of the aftermarket, really) just doesn't seem to be able to get LIN devices right, in my experience.

Thank you for the feedback. I forgot to mention that I did also disconnect the shutter and test the lin bus wire, 12V & ground & all readings were the same. I just needed some reassurance that I was doing it right. I feel much better about searching for an OEM shutter now.