Keyfob issues + ESS eratic

[Judge_Duck]

Hey guys,
Trying to diagnose a few symptoms that ive been experiencing for 2-3 months + a failure to start that happened yesterday after work. Ill describe the fail to start first:

I get in and try to turn Jeep on and it throws up "keyfob not detected" on the dash display. This has been happening randomly, even with a new fob battery. Frustrated, I rapid fire on the start button a few times and eventually the screen changes to the "press start button with fob" message, which I tried to do and still couldnt start. I could also see the red light blinking on the fob each time I tried to press start.

I had to sit for 30-40 minutes waiting on my buddy to bring the other fob, and during this time I saw the radio start up splash screen flash a few times and occasionally the dash screen would show the typical "push clutch + brake to start" message.

I got home and switched batteries, even though it was only about 2 months old on the "broken" fob, and the jeep starts without issue. I put the original battery back in and it starts without issue. I took the battery out and tried pushing the start button with just the fob, and it starts fine.

The other symptoms Im experiencing are:
- Fob buttons stopped working 2.5 months ago, even with new batteries. Red light blinks when pressed, but no response from jeep.
- ESS has been dissappearing randomly in the last two weeks. Oddly enough it worked yesterday on my way to work.
- Not sure if relevant, but the only other thing out of the ordinary is I had my drivers door trim panel off for 3 days, and my lock/unlock buttons were unplugged.

I know the first suggestions are going to be verify battery voltage, which I will do tonight + Im already assuming the aux battery is dead. The dash has been showing normal voltages otherwise, and Ive had 0 codes thrown.

My questions are:
Can a dead aux battery prevent the remote functions of the fobs from working?

Can it also prevent the failsafe "press start button with fob button if fob dead" from working?

Finally: shouldnt the ESS warning light come on if the aux battery is dead?

Let me know if I can provide any other info.

Sponsored

 

[Cartman]

Dead battery in the fob after 2.5 months... could be if the batery was old or noname...just measure it. Flashes of system when you sit on it loks like the car recognize that fob is in.
If you starting with the key, the trasmitor need to be near button, it means that you should press the button with the end where is physical key and the button to flip it.
Dead aux could cause many problems, just replace it and you will see if the problems persist.

 

[Judge_Duck]

At the time, I had tried physically pressing the start button down with the key and it still wouldnt start. My backup keyfob had 0 issues though.

I ran the Jeep on the same batteries (main/aux) for a while to see if I could replicate the issue. Ran it for about 2 weeks and never had the issue again. Batteries tested fine on multimeter, but tested bad at the auto parts store. Ended up replacing main battery and deleting my aux.

Keyfobs still not working so will make seperate post on that -- I believe one of my RF antennas are bad.

In conclusion, I can only blame this on a bad main/aux battery at this point. Will update post if it actually happens again.

 

[Cartman]

I meant the battery in the Fob. not in the car. I think deleting the aux is the wrong way to go, but many people do it and they are ok. The antenna is around the start button and the chip is a 433Mhz superchip when you take the key apart, it seems to me to be a 4A PCF7939M and a SIP22 blade. But I don't think there is anything wrong with it. If one key works and the other doesn't.
1. change the battery in the key and if that doesn't help, then few €/USD
2. delete and re-encode the key. If that doesn't help either, then 50-80€/USD
3. the same person who transcodes it will change the chip and encode the key with the new chip. 5€/USD chip and then coding

 

[Judge_Duck]

Both keys have brand new batteries already and it hasnt helped. I wanted to verify there's nothing wrong inside the jeep before starting to go down the new key path.

I have the basic 3 button fob and no passive entry, do you know which modules in Jscan display antenna info for the basic lock/unlock system? Ive looked under the RF module and the body control module but cannot figure out what data pertains to the basic wireless lock/unlock feature.

 

[THAW]

I have the basic 3 button fob and no passive entry, do you know which modules in Jscan display antenna info for the basic lock/unlock system? Ive looked under the RF module and the body control module but cannot figure out what data pertains to the basic wireless lock/unlock feature.

Sponsored