The 1184-3 code was active when the Product Status Report was downloaded from the ECM. It also shows that same code logged 100 times in the last 100 hours. In other words it's intermittent.
If you're getting 0.00 volts between 42 & 3, and you can see that 1184-3 code active within ET
simultaneously, only then would I suspect the ECM. You need ET connected to diagnose that properly.
Without ET connected it's hard to tell. The interlock system reports to both ECMs...
View attachment 311443
Based on the above, certain pins need to be grounded and certain pins need to be open. The source is the 202 ground wire. Make sure that's good first. If the whole system is bypassed, and you still have your armrest light on, well that's most likely an ECM fault. Which one will be the next thing to determine. And ffs, if you bypass anything, make sure is goes back to how it was after testing. This is how people die.