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Does the starter engage when you try to start the vehicle? Have you confirmed that the battery is good and not weak? Take a look through these links. It shows how to load test the battery. Also, make sure the battery terminals are both clean and tight.
Now, if the battery is good and the starter doesn't engage, I recommend testing the starter relay. It is located on the under hood fuse / relay box. It is item 31 in the relay box. See pictures 1 and 2.
You have two ways of testing the relay. First, locate another relay in the box with the same part number and switch them to see if that makes a difference. Or, follow this link that explains how to test a relay.
Here are a few general links which you may find helpful.
If the starter does engage but the engine fails to start, take a look through this link and let me know any of the specifics.
Let me know if this helps or if you have other questions. Also, you didn't indicate an engine size. The attached pictures are related to a 3.5L V6. If that is incorrect, let me know. Also, the lid of the relay box should have a legend listed on it.
Images (Click to enlarge)
Thursday, April 11th, 2019 AT 6:21 PM