2008 cadillac dts no crank no start

Hey all,

Have a cadillac dts 2008. I had a no start no crank problem so i replaced the starter. I Didn't have a ton of money so bought a brand new tyc starter, and problem seemed resolved until a week later, Won't crank won't Start. I let it sit for few hours and it started right up. Ran fine for 4 months than car sat for 3 weeks and its doing same thing.looking for any ideas what to look at. Please help and thanks in advance

When it doesn’t crank can a scanner communicate with the car? 2nd have you checked the block ground??

Hello thank you for responding. So a scan tool can and will communicate. Only codes were voltage codes due to dead battery. I have not checked block grounds. Also i used relay bypass with on/off switch and car will crank then.Any idea where to get a schematic as I assume there are more than 1 ground? Thanks in advance

You should get battery voltage on the Yellow wire at the control side of the relay when the key is in the Start position. Check the relay pins for power. With key on, you should get one power feed, and with engine in the crank or start position, 2 power feeds. You can check for bad ground by doing a voltage drop or a test light hooked up to ground and touching the engine block. The test light should not light. If it does, you have a bad ground. If you have a good scanner, you can see if the ECM receives a crank signal from the BCM. If it does,and you don't get batt voltage on the control side of the relay, you may look for park/neutral safety switch input in the ecm providing that the car is in park or neutral.