2018 Silverado Periodically won't Start

[Pope]

Hey everyone,  I have  a random gremlin in my 2018 Silverado 5.3.  112K miles.

 

Started a couple of weeks ago when it was cold.  Wouldn't turn over after an hour of being shut down.  All the lights on, no codes, just nothing with the switch.   I had a buddy jump it, but as we were getting the cables on, I was working the shifter into neutral and back and forth.   It started up like it didn't need the jump.  So I get a new battery the next day.  No issues for a few days.  Try to go home from work, same deal.  But it was giving me a throttle body position code.  (don't remember what one) and was in limp mode, but still not power to the starter.  I went under the hood and noticed one of the vacuum connections was not quite tight.  Fixed that, cleared the code.  moved the shifter around and it started up.  Been fine for a week, no codes.  Been waiting for it to happens so I can troubleshoot the neutral switch and starter relay.

 

Happened this morning.  Park and Neutral no start.  Different than turning key in gear.  So don't think it is that.  I took the relay out, tapped it around a bit, put it back.  No change.  Then I sat in the cab and scanned just about every system I could.  No codes.  Tried the ignition again.  Starts right up!   let it run awhile, shut down, open door, starts right up.  Drove to work, same deal, starts right up?

 

Thoughts?   

I think I'll replace the $10 relay and maybe the negative ground cable?  

[rav3]

There are several things that can cause this, so you'll need to check a list off one at a time, since you don't have any codes.

I would start with cleaning ALL grounds. i.e. battery terminal, fire wall grounds, frame grounds and any that I didn't mention.

2. Check all connections at your starter. they need to be clean. Also, your starter gets its ground from mounting to the engine. 

With a bad ground you will get an intermittent start.

3. Swap your starter relay with another one in the engine fuse box. See video below.

4. I think this just came up on a post here about the Neutral lock out on the ignition switch.

 

 

[Pope]

thanks, I saw that video and was going to switch the relays.  Going to go through all the grounds.  I did the frame ground on the passenger side a little big ago.