Hi and thanks for using 2CarPros.
If it always starts when you jump start it, I suspect there is an issue with an electrical connection. Most often, it is at the battery itself. Take a look through this link and let me know if it helps.
https://www.2carpros.com/articles/everything-goes-dead-when-engine-is-cranked
Now, what would be really helpful is when it doesn't start, is to check if the starter is getting power at the solenoid when the key is in the start position. If you can do that, it will really be helpful. Here is a link that shows how it is done:
https://www.2carpros.com/articles/starter-not-working-repair
If that isn't the issue, we need to check the starter relay. Keep in mind, a starter can work one time and not the next. I attached a picture showing which one is the correct one to test. Here is a link that explains how to check a relay:
To be honest, my first suspect is a weak connection at the battery which is improved when a jumper cable clamp is put on it. So, check that first.
Here are a few links that may be helpful to you. I figured I would add them in case you need them.
https://www.2carpros.com/articles/car-battery-load-test
Check out the diagrams (Below). Let us know what happens and please upload pictures or videos of the problem.
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Monday, April 1st, 2019 AT 11:16 AM