I have a 2003 Grand Prix it would turn but it will not start
Make sure you have a good 12 volts at the battery, check all the connections at the battery as well. I would also clean the throttle body good with a throttle body cleaner...
Check the wiring going to the ignition control module. If this is a GT model with the 3.8 L V6 that wiring harness needed to be moved to change the thermostat. Make sure none of the wires got unplugged, damaged, or wet during the repair. HTH. -Jim
There should be 2 wires that are near where you may have be working that go down the back of the engine from the ignition module... the go to the crank sensor ... if they got unplugged that may be your problem good luck
Looking for a Used GMC in your area?
CarGurus has 211,147 nationwide GMC listings starting at $800.