Please help me diagnose an intermittent No-start issue on a 2018 Subaru Outback

I am at the end of my mechanical and electronic rope with a wierd situation involving my ex-wife's car (We co-parent, have a good relationship, I genuinely try to do my best to help her).  Car in question is a 2018 Outback, bought in 2018, and has 70k miles, all dealer serviced. No accidents or issues, garage kept...  Because bullets are easier to follow-

- The car will not start every ~8th time (usually 1 in 5-10 starts).  We've kept track. 

- It's been doing this for about a year now. 

- I fired off the parts cannon in frustration with a new battery, alternator, and FOB batteries (twice), with no change in symptoms. 

- There's no noise/clicking whatsoever when starting , and all interior dash functions illuminate properly.  cycling the key doesn't fix it. 

- Once it starts, there is no issue with drivability or anything. 

- It's been to the dealer several times for this, as well as an independent shop, and they all say the car is fine and can't reproduce the issue.  The starter has been tested as good, and all grounds have supposedly been  inspected and look good.  

- There's no correlation to time the car spends sitting.  It's happened while warm, cold, and everything in between. 

It's really bothering her because her work puts her in some...unsavory neighborhoods, and of course it's always the time that this happens.  She's a pro with the jumper pack now, but it's getting to the point where she wants to trade the car in because of this issue, which I feel is a pretty nuclear option.  Aside from changing the starter, is there anything else this could be?  I initially thought anti-theft, but the fact that it starts fine on a jumper seems to negate this issue?  It doesn't act like it has low voltage- it more just acts like... defiant.  Like, everythings fine, but screw you I don't want to start. 

Any help would be appreciated.  The car is in great shape and I'd hate for her to have to punt on it so early because other than this super frustrating issue, she really loves the car and it's perfect for her. 

Maybe I missed it, but when it doesn't start, what doesn't happen?

(no dash lights, doesn't crank, cranks but doesn't fire, turn the key and everything goes dark, etc)

sounds like jumping it makes it work?

it sounds like dash lights come on and a jump gets it going.  If so,  I'd start by replacing the battery cables. (Or thoroughly testing them).  

jfryjfry said:

Maybe I missed it, but when it doesn't start, what doesn't happen?

(no dash lights, doesn't crank, cranks but doesn't fire, turn the key and everything goes dark, etc)

sounds like jumping it makes it work?

 

it sounds like dash lights come on and a jump gets it going.  If so,  I'd start by replacing the battery cables. (Or thoroughly testing them).  

Dash lights illuminate as normal, just nothing from the starter- no clicking, nothing...  Everything else acts normally upon startup except the car actually starting. No dimming of dash/interior lights either...  It doesn't feel to me like lack of volatge, but more that voltage not getting to the starter properly... but then why does jumping it work?!  That's what has me confused.

Had a somewhat similar issue where the main ground looked good but actually didn't have a solid connection, sometimes it would turn the interior lights on sometimes nothing. Sanded it and everything was good, easy and free thing to try 

Question: When using the jump pack, are you connecting directly to both battery posts, or one to the positive post and one to another ground point? 

Motojunky said:

Question: When using the jump pack, are you connecting directly to both battery posts, or one to the positive post and one to another ground point? 

Both battery terminals.  I thought of this too.  I guess I'll have to go through the grounding points again, it can't hurt.  I've already done it and couldn't find any smoking gun, but maybe like mentioned I'll pull them all and make absolutely sure by sanding them. 

As an earlier poster suggested, I'd be inclined to replace the battery cables. That said, the last couple that I've bought from my FLAPS have been decidedly cheap feeling.

I mean battery cables and a starter would be what I change next. Def sounds like the starter is jacked up. 

Do you have an ODB2 scanner (or dongle) that'll read battery voltage when the no-start situation happens?  I was leaning towards the starter, but the fact that it starts 100% with the jump pack makes me question that.  My wife had an issue with her battery where it registered good voltage across the terminals, but when I threw it on a load tester it was obviously a bad battery.

Also, is there corrosion build-up on the terminals?  I've also seen this cause an intermittent no-start condition in the past.

Since it's such a weird problem it probably has a weird answer. 
 

Maybe a bad fuse? Is there one for the starter or relay?

Sounds like the jumper pack is adding enough juice to close an open circuit somewhere. 

dj06482 (Forum Supporter) said:

Do you have an ODB2 scanner (or dongle) that'll read battery voltage when the no-start situation happens?  I was leaning towards the starter, but the fact that it starts 100% with the jump pack makes me question that.  My wife had an issue with her battery where it registered good voltage across the terminals, but when I threw it on a load tester it was obviously a bad battery.

Also, is there corrosion build-up on the terminals?  I've also seen this cause an intermittent no-start condition in the past.

I do, the problem lies in that I don't drive the vehicle myself very often.  I think I'm gonna take it for a week or so and do more troubleshooting. 

These are all good suggestions, I really appreciate it! 

I can't come up with a scenario which logically is solved by a jumper battery, but one other area to think about is any switches that would prevent the computer (or other digital logic) from trying to engage the starter.    Since there's no click or anything from the starter, maybe it's something like an intermittant brake or transmission park switch or something like that?  No idea why a jumper battery would help in that case, though.

I have seen a couple scenarios where someone thinks that jumping the car helps it start and it's just a intermittent issue. (If they kept making additional attempts to start it without jumping it, it would have eventually started anyway)

So I'm not entirely sure how much weight to put on that data point. 

It's probably a failing starter.  It may not click like you'd expect it to.

Is it something weird like a hairband on the shifter that isn't quite allowing park, or a bejeweled ring around the start button causing the transponder signal from the key to not work?

Is the anti theft light coming on?

Will it start easily if put in neutral?

I'm wondering if there's corrosion on the battery terminals, and the clamping of the jump pack onto the battery makes for a better connection.

I once had a '98 Camry that had an intermittent no-start based on the terminals corroding. Clean the corrosion off, and the car would start just fine. The Toyotas I've owned seem to build up corrosion on the negative battery terminal like no other vehicle I've owned (our Rav4 does it to, and has had probably 5 different batteries over its lifetime).

My guess is a mega fuse or something similar is going bad. The battery slowly drains and then won't start. The extra juice from the jump pack bridges the connection. 
 

Change all the grounds. 

So I grabbed the car yesterday to do some more troubleshooting, and I didn't have to wait long because it wouldn't start this morning, haha.  Here's what I know, in no apparent order- 

- All lights, dash functions as normal

- no anti-theft lights or warnings

- battery across the terminals was 12.7v, and no change when trying to start it. 

- there was no 12v power at the starter when my wife tried to start it. 

- All power connections to the best of my ability felt tight, and battery terminals looked great (battery is <1 year old). 

- There are/were no hair doo-dads, glitzy rings, or bedazzlements anywhere in the car or on the fob. 

- Starting in neutral yielded the same no-start result, as did wiggling in P. 

I hooked up the jumper pack to both battery terminals, voltage across jumped to 14.7.  I didn't get under the car to check the starter, because obviously it was powered and started right up.  So all of that leads me to believe that it's something electrical/fuse/ECM related and not starter related, but I guess I could be wrong.  At the very least, I can rule out any shift switches and most grounds, right?  I feel like there's a relay somewhere that's going bad but not all the way there, where the voltage spike from the jumper pack is energizing it enough to overcome the circuit, but I'm not an electrical engineer, so I'll defer to the hive. 

This one is definitely interesting, ha.  

Is it possible the starter solenoid is sticking?  Have you tried tapping it gently with a BFH when it happens?

I had to replace the ignition switch on our Impreza for an intermittent no crank problem. It was a 1996, but...

My vote is ignition switch as well.  Usually those fail intermittent until they die completely.