Q: My 2009 Cadillac CTS won't start

I’m a bit concerned about your description of using a jumper wire to ground at the starter relay. Either you can make the starter motor turn from here, which you could if you jumper the correct terminals with power, or you used a jumper wire and something shorted out. Which one of these is the case is not exactly clear. If you did short something out, this becomes more complicated.

Your Cadillac relies on the ECM (engine control module) and the BCM (body control module) to start your car. For this reason, you will need a scanner that can access data from your car. These modules communicate via data lines that only a computer can make sense of. Also, there are four separate wires going into the starter relay. Each one needs to be treated differently and this can only be determined with a wiring diagram. If you don’t have access to these two items, I recommend having a certified technician inspect the starting problem in person in order to get this properly diagnosed and repaired.