Technical Intermittent No Start

[DetergentCandy]

Hey y'all! I have a 2017 Jeep Renegade, and since it's essentially a 500X, I'm wondering if maybe I can find some help here.

I've posted about this over on the Jeep Renegade Forums and still not able to find an answer. If you want to read it from the source, it's here.

When getting in to start the vehicle, the push button does the thing and turns on the accessories, but sometimes it fails to actually start. There is no cranking attempt. It just doesn't start, and the battery icon on the dash illuminates. There's no CEL and no codes pending or stored. Sometimes the info display displays "Sound System Unavailable." I'll sit there and push the button over and over and eventually it starts sometimes. But other times I may have to come back in 30 minutes and then it starts on that attempt.

Battery test is good at 13V. And when we test the battery when the engine is running, it's 15V (probably 14.8 but my meter doesn't display decimals so I'm guessing it's rounding up). So I dunno if it's a battery/alternator issue.
I took the battery to Batteries Plus and they tested it overnight and said it's a good battery. However, I'm still going to buy my own load tester today just to confirm myself. I'm not actually sure if Batteries Plus did a load test or just a charge and test.
Battery cables and terminals are tight and in good condition.

We checked and swapped the starter relay thinking maybe that was it, but it's still having the same issues.

We also replaced the brake switch in-case that was preventing the engine from starting, but that didn't fix it. As soon as I attempted to start it after installing the new switch it failed to start. This time, I confirmed my foot remained on the brake. I pressed the brake, and pushed the start button. Accessories turned on, but the engine did not start. I waited a few seconds and pushed the button again, and still no engine start. Then I gave the button a pretty firm and quick tap with the tip of my finger and it started.

Since the push-start button just, doesn't start the engine sometimes, and other times it does, I'm wondering if this could just be a failing ignition button? I'm unsure since the button at least ALWAYS turns the accessories on. It just sometimes doesn't start the engine. Can the button work for the accessories but not work for the ignition? I assume it's just a single button inside without a secondary indent or anything, so I don't know if the button would be able to do one but then fail to do the other when it's all the same single button press.

 

[bugsymike]

Modern car electrics can be a right pain, Is it possible to access the wires coming out of the start switch to see if it is actually sending a signal to the ECU when it fails to start?
I had a 2014 Vauxhall Combo (Fiat Doblo 1.3MJ in drag) that would cut out at the first junction from cold starting as you came to a halt, I thought it may be related to the Stop/Start function switch, but it turned out to be the clutch pedal sensor where a tag had broken off. It would not restart by just turning the key, I had to remove the key, lock and unlock the car and then it would start. Obviously not applicable if yours is an automatic.
Another thought what diagnostics are you using to read for Error codes as basic tools are not comprehensive enough, many on Forum use MES full version, not sure if it recognises Jeep. Apart from that I have found Snap On Zeus good if you know someone with it.

 

[DetergentCandy]

Modern car electrics can be a right pain, Is it possible to access the wires coming out of the start switch to see if it is actually sending a signal to the ECU when it fails to start?
I had a 2014 Vauxhall Combo (Fiat Doblo 1.3MJ in drag) that would cut out at the first junction from cold starting as you came to a halt, I thought it may be related to the Stop/Start function switch, but it turned out to be the clutch pedal sensor where a tag had broken off. It would not restart by just turning the key, I had to remove the key, lock and unlock the car and then it would start. Obviously not applicable if yours is an automatic.
Another thought what diagnostics are you using to read for Error codes as basic tools are not comprehensive enough, many on Forum use MES full version, not sure if it recognises Jeep. Apart from that I have found Snap On Zeus good if you know someone with it.

They really are a pain. I'm not trying to sound like an old fool (I'm only 30 or 40 years old), but a traditional turn key ignition will always be my preference I've never been a fan of push-button ignitions.

And yeah, this one is the 7-speed automatic for reference. Doubt that plays into the ignition problems but I didn't include it in my OP and think it might be helpful information.

For error codes I'm using a simple Pocket Scan tool. It only reads active and pending error codes.
BUT, I did just buy a BlueDriver OBDII scan tool that I'm hoping will give me more information.
I don't know anything about MES but I'll look into it. Is that like VW's VAGCOM?

I'm about to head out to the garage to dink around some more with the Jeep. I've got the BlueDriver to try out, as well as a load tester for the battery. I recently replaced all 4 motor mounts and just now realized that was possibly around the time the ignition started acting up. So while I don't want to say it's correlated, I still want to make sure I didn't pinch any wires or leave any electrical connectors or harnesses loose.

 

[bugsymike]

They really are a pain. I'm not trying to sound like an old fool (I'm only 30 or 40 years old), but a traditional turn key ignition will always be my preference I've never been a fan of push-button ignitions.

And yeah, this one is the 7-speed automatic for reference. Doubt that plays into the ignition problems but I didn't include it in my OP and think it might be helpful information.

For error codes I'm using a simple Pocket Scan tool. It only reads active and pending error codes.
BUT, I did just buy a BlueDriver OBDII scan tool that I'm hoping will give me more information.
I don't know anything about MES but I'll look into it. Is that like VW's VAGCOM?

I'm about to head out to the garage to dink around some more with the Jeep. I've got the BlueDriver to try out, as well as a load tester for the battery. I recently replaced all 4 motor mounts and just now realized that was possibly around the time the ignition started acting up. So while I don't want to say it's correlated, I still want to make sure I didn't pinch any wires or leave any electrical connectors or harnesses loose.

Ha,ha, speaking as an old fool of 73, but over 50 in motor trade in my defence.
Automatics do have a safety feature of preventing starting whilst in gear for obvious reasons, in the old days it was a inhibitor switch by the gear selector usually, however on modern vehicle it will be controlled by a sensor on the gearbox talking to the ECU.I have not used Vagcom but heard it it is good.
The MultiEcuScan tool can be read on tablets etc using Windows 10 or 11 and if you go on their website it will tell you what versions will do what tasks and is Fiat specific which is why it is very popular on Fiat Forum, so many here can advise on what results you should see when testing.
Personally at the time of purchase I owned a Fiat Scudo 8 seater that uses the Peugeot engine and the MES was not compatible with it, however Gendan the UK dealers for it advised me that MaxiEcu was the tool for the job, it also had the benefit that for an additional £30 roughly a time, I could add additional manufacturer licenses so for me that was quite useful.
Both MES and my tool will read and delete codes, activate sensors and functions and do lots of other things including ABS fault code readings and "proxi alignment" to let computer recognise changes to the system and much more.
Obviously either of these full version scanners are much more expensive than a basic code reader, but probably soon pay for themselves when paying for a dealer to scan your car.

 

[DetergentCandy]

Okay, so I dug some more and... didn't get many answers lol

The battery tested fine with the load tester.

So I essentially went through the process of replacing the motor mounts again (without actually replacing them of course) but everything looked right. No harnesses being pulled. No connectors loose. No exposed wires. So, I don't think I did anything to cause the ignition issues when I installed the new mounts.

After all that, I went to pull it back out of the garage and got a CEL, U1408 - implausible brake signal. So that's fun. I've cleared the code and it hasn't come back yet, but now I'm even more unsure about what's going on. As I said in my first post, I did replace the brake signal switch, but other than that, I haven't touched the brakes or anything revolving around them.

 

[DetergentCandy]

Also, something I've been noticing that I'm now not sure if I've ever noticed before is this symbol on the dash.

"Electronic Throttle Control" warning.
It comes on when the accessories are on, and then it goes off when the engine is running. Is that normal operation? Or should it not even be on when the accessories are on?

 

[bugsymike]

Okay, so I dug some more and... didn't get many answers lol

The battery tested fine with the load tester.

So I essentially went through the process of replacing the motor mounts again (without actually replacing them of course) but everything looked right. No harnesses being pulled. No connectors loose. No exposed wires. So, I don't think I did anything to cause the ignition issues when I installed the new mounts.

After all that, I went to pull it back out of the garage and got a CEL, U1408 - implausible brake signal. So that's fun. I've cleared the code and it hasn't come back yet, but now I'm even more unsure about what's going on. As I said in my first post, I did replace the brake signal switch, but other than that, I haven't touched the brakes or anything revolving around them.

There is a mention on the Fiat 500 Forum about that error code mentioning the electronic handbrake, it may be worth reading that if applicable to your car.

 

[Mike1alike]

The U1408 code is important. It means the body computer is seeing an implausible brake signal (the two brake inputs don’t agree). On these vehicles the BCM must see a valid brake signal before it will allow the starter to crank.
So even if the accessories come on, the car may refuse to crank if the brake signals don’t match.
Since you already replaced the brake switch, it would be worth checking the connector, wiring, and switch adjustment. An aftermarket switch can also cause this if its internal contacts don’t match the original logic.

 

[DetergentCandy]

There is a mention on the Fiat 500 Forum about that error code mentioning the electronic handbrake, it may be worth reading that if applicable to your car.

Oooh, I'll check into that! I appreciate it.

The U1408 code is important. It means the body computer is seeing an implausible brake signal (the two brake inputs don’t agree). On these vehicles the BCM must see a valid brake signal before it will allow the starter to crank.
So even if the accessories come on, the car may refuse to crank if the brake signals don’t match.
Since you already replaced the brake switch, it would be worth checking the connector, wiring, and switch adjustment. An aftermarket switch can also cause this if its internal contacts don’t match the original logic.

Thanks! The brake switch looked identical to the factory one, even down to the markings and the color of plastic. But as you said, maybe the internals aren't identical.
We're currently not driving it because of the starting issues but I'll go out and give it a couple runs. Driving around the neighborhood might cause the code to come back as it only came on those 2 times and is currently not present.

 

[porta]

Have you tried new batteries on the fob
The wife’s renegade has two, one fob has been swapped for the other as the car started doing exactly what yours did, intermittent non start and strange ‘communication codes’. Newer fob, cleared codes, all good BUT she still hasn’t changed batteries in other fob

 

[DetergentCandy]

Have you tried new batteries on the fob
The wife’s renegade has two, one fob has been swapped for the other as the car started doing exactly what yours did, intermittent non start and strange ‘communication codes’. Newer fob, cleared codes, all good BUT she still hasn’t changed batteries in other fob

Yeah, we replaced them but I can't remember how recently. I feel like the factory batteries lasted significantly longer than the ones we've replaced cause I think we've replaced them a couple times. I'll double check and just replace the batteries for good measure.

 

[Mike1alike]

Have you tried new batteries on the fob
The wife’s renegade has two, one fob has been swapped for the other as the car started doing exactly what yours did, intermittent non start and strange ‘communication codes’. Newer fob, cleared codes, all good BUT she still hasn’t changed batteries in other fob

That is amazing! I wouldn't have thought of that as a possible reason or at least wouldn't be in the top suspects.
Great that you mentioned it.
Would be something if that's the culprit here, too.

 

[DetergentCandy]

Would be something if that's the culprit here, too.

I sure was hoping that would be it! But both remote batteries tested at 3.05v
So it's not the remotes.

However, that doesn't rule out the remotes OR the vehicle transponder. Just because the batteries are good doesn't mean the remotes are good. It's possible something else is going on. And I only say that because it has never failed to start when pressing the remote to the start button.

I really don't like it, but I have an appointment tomorrow afternoon at the Jeep dealership. Really don't want to have to do that, but if it's a network or computer problem... I'm way out of my element for a diagnosis. I was hoping a starter or alternator or throttle body or something would be an obvious replacement. But that doesn't seem to be the case with this...

 

[bugsymike]

I sure was hoping that would be it! But both remote batteries tested at 3.05v
So it's not the remotes.

However, that doesn't rule out the remotes OR the vehicle transponder. Just because the batteries are good doesn't mean the remotes are good. It's possible something else is going on. And I only say that because it has never failed to start when pressing the remote to the start button.

I really don't like it, but I have an appointment tomorrow afternoon at the Jeep dealership. Really don't want to have to do that, but if it's a network or computer problem... I'm way out of my element for a diagnosis. I was hoping a starter or alternator or throttle body or something would be an obvious replacement. But that doesn't seem to be the case with this...

Any chance it is a known "recall issue" that Dealership should fix FOC?

 

[porta]

I sure was hoping that would be it! But both remote batteries tested at 3.05v
So it's not the remotes.

However, that doesn't rule out the remotes OR the vehicle transponder. Just because the batteries are good doesn't mean the remotes are good. It's possible something else is going on. And I only say that because it has never failed to start when pressing the remote to the start button.

I really don't like it, but I have an appointment tomorrow afternoon at the Jeep dealership. Really don't want to have to do that, but if it's a network or computer problem... I'm way out of my element for a diagnosis. I was hoping a starter or alternator or throttle body or something would be an obvious replacement. But that doesn't seem to be the case with this...

I’d better get batteries for our dud remote and check it’s not a fob issue

 

[porta]

That is amazing! I wouldn't have thought of that as a possible reason or at least wouldn't be in the top suspects.
Great that you mentioned it.
Would be something if that's the culprit here, too.

It seems to be a common issue with many manufacturers…I only noticed it wehn using the ‘spare’ fob, after wife had swapped them, and there were odd codes and a symbol (as above) that id never seen before. Luckily MES covers Fiat based Jeeps so could interrogate the system, turns out they were all ‘poor communication’ errors with one being proximity of fob…that’s wehn it clicked about being a battery issue

 

[DetergentCandy]

Well, the Jeep dealer has the Renegade now. They said 3-5 days for their diagnostics. At least we have a spare car so we're good for now.
Strangely as I pulled into the service department I got a CEL
P0571 and U1408 which are both related to the brakes. So... hopefully it's as simple as a switch or a relay or something not engaging and the ECU not knowing whether the brake is being pressed to start the engine.

Either that or it's unrelated and just telling me I borked the brake switch replacement

 

[Mike1alike]

So... hopefully it's as simple as a switch or a relay or something not engaging and the ECU not knowing whether the brake is being pressed to start the engine.

It really sounds like a problem with brake switch wiring. Most probably oxidised contacts on that plug.

 

[DetergentCandy]

It really sounds like a problem with brake switch wiring. Most probably oxidised contacts on that plug.

I would LOVE for it to be that simple. It has definitely seen mud, water, and snow here in Colorado.

 

[Mike1alike]

I would LOVE for it to be that simple. It has definitely seen mud, water, and snow here in Colorado.

You'll know soon. I wish you it is!