Cadillac Repair Questions? Ask a Mechanic for Answers ASAP
I would try a new relay first.
Here is the wiring diagram,
Remove the starter relay when it's acting up and test the socket for voltage at each terminal. One spot should be hot all the time. That is the spot coming from the starter fuse and eventually the battery. A second should be hot with the key on start and start. That comes from the ignition relay, so let's begin with these 2 tests. Let me know the outcome.
Ok, technically it doesn't go to ground just yet, it goes to the ecm. Then the ecm grounds the relay depending of course on the crank signal from the ignition switch and/or the park/neutral signal from the transmission. Now, to determine which. I would gain access to the ecm and test for a voltage at pin 31 where the yellow wire comes in from the ignition switch in crank mode. Test it when the starter isn't engaging so you know the problem is occurring. If there is no voltage at pin 31, then it's a short in that yellow wire or the ignition switch may be bad. If there is no voltage test again leaving the ignition switch.
If there is voltage at pin 31, then test for a signal from the park/neutral switch at pin 32. This may be 12 volts or it may be only 5 volts. Also, the next time this problems happens try moving the shifter all the way from park to low and back and forth while holding the key on start. If at any spot the starter engages except park or neutral, then the transmission park/neutral switch is bad or needs adjusting, if there is even an adjustment for it.
The Electronic Control Module (ECM) is located to the left of the throttle body, and just above the drive belt.
Sorry, I was out.