2011 JKU sputtering on cold start

jkwhite

jkwhite

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Joined
Sep 28, 2019
Messages
7
Location
Washington
I have a 2011 JKU that when the weather is cooler out it sputters on start. it gives me these codes P2100, C121C, U0401 and I have looked up all the codes. With that being said I replaced my throttle body actuator and had the dealership flash the new throttle body actuator in and though that fixed the problem. It did not so I limped it to the dealership and upon arrival I shut it off to have it looked at. When the service manager told me to bring it in I started it up and it ran just fine with no issues. Should be noted that the red lightening bolt and the anti slip come on and it goes into limp mode and runs rough and no throttle response.

The dealership could not duplicate the problem and they did not have any codes for it. I left it there and the eventually got to it and said when they started it after sitting in the warm shop it was fine and no codes. I took it home and the next day started it up and it ran fine. I was thinking they jiggled a wire and the problem was fixed for now.

The next day I started it that cooler morning and it did the same thing as stated above and I limped it back down to the dealership and they left it run because it was lunch time and they wanted the tech to too see what it was doing. When they shut it off they started it up again and is said that the codes were stored but it was running fine.

I brought it home and this morning it is 50 degrees out and I tried an experiment and started my jeep. The same issue popped back p with the same codes and red lightning bolt and anti slip light staying on. I let the engine warm up for 10 minutes and shut the jeep off. I then started it up again and it is running just fine.

I am looking for help on this issue I know it has to be environmental wand temperature related but I can not find anything anywhere on this issue.

I also had the catalytic convertors checked and they are fine.

2011 Jeep JKU
Auto transmission
3.8L motor
cold air intake, throttle body spacer ( both have been on for several years)
2.5 inch lift
magnaflow muffler
33" tires
 
Well, the U0401 code usually means one of the following:
  • A dead battery
  • ECM problems
  • A problem with the CAN bus
The P2100 code I'm assuming is gone now since you had the throttle body actuator replaced, yes? Are those the three codes it's still throwing, or are some of them gone and maybe there are new ones?

It definitely sounds electrical / sensor related.
 
Take the throttle body spacer off just to see what happens. Throttle body spacers do not work in fuel injected vehicles. That’s a well known myth / scam.

Try that out or curiosity.

If it’s temp related, it could be the coolant temp sensor.
 
Also, I asked a friend about this and here's what he said:

"One cold morning I got in my Jeep to start it. It was sputtering like it was missing almost like it had water in the gas brought it to town came back home it was running a little bit better but with the engine light on. It did the same thing the next day. I told my husband I think the spark plugs need to be changed we have it 2007 with low mileage well he changed all the spark plugs and noticed one of the spark plug wire was torn causing it to sputter. He changed all the spark plug wires and spark plugs now it runs and purrs like a kitty cat. Couldn't figure out how these wires got pulled away from its own connection."
 
I took the throttle body spacer off and no change. I had forgot to say that it has a second or two second hesitation before it engages the starter. It only does that with this problem I have not ever had a hesitation before.

changed plugs and wires about 20k miles ago. Good possibility but I can't even get the fuel pedal to boost the rpm when it is doing it. It just runs about 1200 rpm and basically I have idled it to the dealership so I'm fairly certain it is not plugs of wires but I could be wrong. I checked all the plug wires and they are tight and seated.
 
Consider me puzzled then. No mechanic has been able to figure it out?

An OBDII scanner with live diagnostics would help. Then you could plug it in and monitor things while you drive it. That feedback might be telling.
 
Chris said:
Consider me puzzled then. No mechanic has been able to figure it out?

An OBDII scanner with live diagnostics would help. Then you could plug it in and monitor things while you drive it. That feedback might be telling.
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I am taking it back to the shop Tuesday so they can trace wires. I am at a loss too.
 
jkwhite said:
I am taking it back to the shop Tuesday so they can trace wires. I am at a loss too.
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I hope they figure it out (let us know if they do).

This is one of those things that would have me losing my mind. Most things are easy to figure out, but this sounds like it's a potential wiring / electrical issue.
 
Ok so the dealership just called and they traced it to a fuel injector that was only getting continuity when it was warm. They are not changing the whole harness as it would be over $800 for it they are running a bypass wire instead and saving a few hundred dollars.
 
  • Wow
Reactions: Chris
Wow, I guess it's a good thing you took it in. That's one of those things that I never would have even guessed in a million years. Sometimes you have to be a damn electrician to figure these things out.
 
Ok so it seams this issue is common as can be. I have the lightning bolt and p0507, I have replaced throttle body 2 times, the PCM, the battery, alternator,air temp sensor, both B1 O2, the PCV, the PCV hose, accelerator pedal. I have checked for vacuum leaks 5 times with help from a very good mechanic. next I’m going to get all the spark plugs,wires and coil box/distribution box(whatever you want to call it). I heard about a cam shaft sensor I wil try as well. If anyone has advise, shoot it over, I’ll try it out. Soon I will be at a loss and forced to bring it to the dealer. (For the LS swappers, if you would please send all the parts or the cash for it, I would gladly get it done)
 
VG1586 said:
Ok so it seams this issue is common as can be. I have the lightning bolt and p0507, I have replaced throttle body 2 times, the PCM, the battery, alternator,air temp sensor, both B1 O2, the PCV, the PCV hose, accelerator pedal. I have checked for vacuum leaks 5 times with help from a very good mechanic. next I’m going to get all the spark plugs,wires and coil box/distribution box(whatever you want to call it). I heard about a cam shaft sensor I wil try as well. If anyone has advise, shoot it over, I’ll try it out. Soon I will be at a loss and forced to bring it to the dealer. (For the LS swappers, if you would please send all the parts or the cash for it, I would gladly get it done)
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When you change the TB you need to do a reset, I had to when I put my Viper TB on.

You need to do this in 15 seconds:

Turn key to on
Wait for the dash lights to go out
Slowly push pedal to floor
Slowly back up
Turn key off
Start the Jeep up

The first time I did the reset it didn't seem to work so a couple days later I did it again only just the pedal down and up a little faster and never had any more lightning bolts. Also whenever you would get a lightning bolt just turn the Jeep off then start it back up and it will be ok again.
 
BLACKJKU said:
When you change the TB you need to do a reset, I had to when I put my Viper TB on.

You need to do this in 15 seconds:

Turn key to on
Wait for the dash lights to go out
Slowly push pedal to floor
Slowly back up
Turn key off
Start the Jeep up

The first time I did the reset it didn't seem to work so a couple days later I did it again only just the pedal down and up a little faster and never had any more lightning bolts. Also whenever you would get a lightning bolt just turn the Jeep off then start it back up and it will be ok again.
Click to expand...

Ok I just finished putting the wires plugs and coil pack in. I did the reset steps and let it l idle for about 10 to 20 min the lightning bolt came back on during idle again and not sure what to do now. The sparkplug defiantly needed changed so it was good for the jeep. I'll keep folks posted on what happens next also the p0507 is still a mystery. If anything is found out I will get the solution posted. Thanks for the help for sure ill take all.i can get at this point.
 
VG1586 said:
Ok I just finished putting the wires plugs and coil pack in. I did the reset steps and let it l idle for about 10 to 20 min the lightning bolt came back on during idle again and not sure what to do now. The sparkplug defiantly needed changed so it was good for the jeep. I'll keep folks posted on what happens next also the p0507 is still a mystery. If anything is found out I will get the solution posted. Thanks for the help for sure ill take all.i can get at this point.
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Did you use OEM tuneup parts, from what i've heard these Jeeps are real picky on what gets installed on them?
 
I did use OEM dealer parts, my mechanic told me the same thing, that the Jeeps can be picky especially with the electronics. I think I will try the cam shaft sensor next then take it in to see if it’s faulty wiring or something of the sort. Maybe they can trace something out that I can’t with their diagnostic computer.
 
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