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Stiff Brake Pedal After Sitting

Cracker_Box

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The vacuum for the booster is supplied by an electric vacuum pump that sits below/under the alternator, being that this setup is not typical for most N/A engine vehicles it is very well possible that the vacuum system isn't design to hold for long once the ignition is switched off. Which would cause the stuff pedal.

I'm a tech for Audi we have similar stuff on our diesel engines and I've noticed it with them before on occasion.
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Bigtuna33

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The vacuum for the booster is supplied by an electric vacuum pump that sits below/under the alternator, being that this setup is not typical for most N/A engine vehicles it is very well possible that the vacuum system isn't design to hold for long once the ignition is switched off. Which would cause the stuff pedal.

I'm a tech for Audi we have similar stuff on our diesel engines and I've noticed it with them before on occasion.
Makes sense; is there a solution or just have to live with it?
 

tobyw

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Mine just started doing this Sunday morning... ~9,500 miles and never had the issue before, but both starts since Sunday morning have required massive brake pedal pressure before the push button would recognize anything and allow it to start?? It makes me wonder if there is a check valve or something in the system between the vacuum pump and the booster that is failing and allowing the vacuum to release rather than being stored in the system for startup?
 

The Fixer

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My wife's JLUS has this happen on occasion. We've had it since May '18 and put 12K miles on it. My JLS has not had this happen yet; got mine in July '19 and have ~3500 miles on it.
 

Mlentz

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It doesn't appear that anyone has reported this issue on the forum...wondering if it's only me? For the last 3 weeks, when I get into the Jeep after it's been sitting a few hours, the brake pedal is VERY stiff. It's like you pumped it while the car was off is the only way I can describe it. As soon as it start up, all is fine. I have 4000 miles on it and it just started happening. Its clockwork the last 3 weeks and when my service appointment finally came OF COURSE the damn thing was fine (so they reported). I did go over and check it myself because they claimed they were driving it and I made clear the issue can be noticed only before startup. I made mention that my very limited research pointed to the brake booster or a vacuum leak but that's just a guess from my Google searches. So, needless to say, I got the car home and it immediately behaved abnormally BUT it did have a couple instances where it worked as expected. So not sure - these intermittent things make me crazy. Tonight when I pulled it into the garage, I notice that after I depressed the brake and let off - there was a strange noise for about 15-20 seconds. Not sure what that was but it seems to be reproducible so if nothing else I'll bring it back this week and ask what that noise is because I never heard that before. Anyone have thoughts on what this could be? THANKS MUCH!
This happened to me last night. I went to start my car after only about 20min of it sitting. I couldn’t press down on the pedal all the way. After 15min of me trying to start it, I pushed down all the way and felt like I was braking the pedal. Finally it started and I took it straight home and had it towed to the dealership. It’s a brand new 2020 Wrangler with 4000 miles and Iv already had to take into the shop once. Of course they called me today and said they couldn’t find anything wrong with it. I know once I pick it up, it will act up again. If anyone has figured out why it’s happening and/or if it’s stopped please let me know! Scared to drive it now!
 

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This happened to me last night. I went to start my car after only about 20min of it sitting. I couldn’t press down on the pedal all the way. After 15min of me trying to start it, I pushed down all the way and felt like I was braking the pedal. Finally it started and I took it straight home and had it towed to the dealership. It’s a brand new 2020 Wrangler with 4000 miles and Iv already had to take into the shop once. Of course they called me today and said they couldn’t find anything wrong with it. I know once I pick it up, it will act up again. If anyone has figured out why it’s happening and/or if it’s stopped please let me know! Scared to drive it now!
You won't break the pedal. I was one of the first people to report this and find the workaround. It works 100% the time if I give it a firm push. It seems that it takes a certain amount of effort to trip the signal that the pedal is in fact pushed in. Annoying but don't bother with the dealer. I've never mentioned it because if you don't have something glaring like a piston physically sticking out of the hood they won't be able to reproduce it.
 
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bbradshaw14

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This happened to me last night. I went to start my car after only about 20min of it sitting. I couldn’t press down on the pedal all the way. After 15min of me trying to start it, I pushed down all the way and felt like I was braking the pedal. Finally it started and I took it straight home and had it towed to the dealership. It’s a brand new 2020 Wrangler with 4000 miles and Iv already had to take into the shop once. Of course they called me today and said they couldn’t find anything wrong with it. I know once I pick it up, it will act up again. If anyone has figured out why it’s happening and/or if it’s stopped please let me know! Scared to drive it now!
I have 22,000 miles now and the issues comes and goes. Nothing major to report and the dealer either is or pretends to be clueless. I’ve always been able to get it to start by pressing harder than. Normal when it happens so have lived with it. A little annoying for a $52,000 vehicle but won’t stop me from getting another one in a year and a half. Good luck!
 

carpendj

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I have the same problem on most days. 2020 Wrangler Unlimited Willys - 3.6 Auto with ESS. Purchased new in August 2020 and I have only covered around 1700 miles. I park the jeep in my garage overnight. I got into it one morning and noted that the brake pedal was super stiff. Hardly any movement at all. Tried to start it and it would not start. If you want to experience it for yourself, simply try to start your jeep without touching the brake pedal. I was about to get it towed but somehow had a hunch to push down on the brake pedal as hard as I could. It then started. I have taken it to the dealer twice and they cannot find any problems. They even kept it overnight and of course, it did not fail for them the next morning. They gave me a loaner Gladiator and it even happened to me once in that. Gladiator was parked on my driveway overnight and it started no problem. Drove to a coffee shop, went in and grabbed a coffee, came out and the brake pedal was stiff and it would not start. Seems to me that there is some issue here and either Jeep are not aware of it or they have not yet found a solution. I have found that you either have to push the pedal down real hard OR you can use the remote start function on your keyfob if you have that option. I tried scanning for codes myself and came back with nothing wrong. My jeep dealer says that they cannot contact Jeep technical support because they have not seen the issue and my Jeep is not reporting any issues. Its very frustrating to be honest. I am keeping on eye on this forum hoping that someone finds a solution.
 

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Probably battery related?
 

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bbradshaw14

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I have the same problem on most days. 2020 Wrangler Unlimited Willys - 3.6 Auto with ESS. Purchased new in August 2020 and I have only covered around 1700 miles. I park the jeep in my garage overnight. I got into it one morning and noted that the brake pedal was super stiff. Hardly any movement at all. Tried to start it and it would not start. If you want to experience it for yourself, simply try to start your jeep without touching the brake pedal. I was about to get it towed but somehow had a hunch to push down on the brake pedal as hard as I could. It then started. I have taken it to the dealer twice and they cannot find any problems. They even kept it overnight and of course, it did not fail for them the next morning. They gave me a loaner Gladiator and it even happened to me once in that. Gladiator was parked on my driveway overnight and it started no problem. Drove to a coffee shop, went in and grabbed a coffee, came out and the brake pedal was stiff and it would not start. Seems to me that there is some issue here and either Jeep are not aware of it or they have not yet found a solution. I have found that you either have to push the pedal down real hard OR you can use the remote start function on your keyfob if you have that option. I tried scanning for codes myself and came back with nothing wrong. My jeep dealer says that they cannot contact Jeep technical support because they have not seen the issue and my Jeep is not reporting any issues. Its very frustrating to be honest. I am keeping on eye on this forum hoping that someone finds a solution.
Nothing was ever found on mine but I will say that over the years it happened less and less. I traded it in on Dec 19th for a 2021 so that solved it for me. Earlier in this thread someone mentioned this being related to the vacuum system and I believe they are right on. Here is additional info I found in a Google search.

https://techtalk.mpbrakes.com/how-to-series/how-to-diagnosing-a-hard-brake-pedal

Nothing ever happened as a result of this - never a braking issue, indicator light, or anything else but sure was annoying. Good Luck!
 

Snstlr140

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Same problem here. Brake goes stiff after about 12-24 hours of sitting. Brand new 2021 JLRU 300 miles on it. Starts if I push really hard on the brake pedal or just use the remote start, then the pedal functions normally. Following incase someone comes up with a solution.
 

mwilk012

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Nobody will ever come up with a solution because there isn’t a real problem. It is at worst a mild inconvenience. The vacuum system is not 100% sealed.
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