Had this 2015 wrangler Willy’s for 5 years. Recently started having ABS issues. Now Speedo not working and won’t leave first gear. Has code that comes up immediately when reset. U0121. Google suggested starting with check fuses and found this jumper in fuse block in what it says is the abs pump/esb spot. Followed it around and it goes across the fire wall and then through the firewall near the booster and and the goes under drivers side floor mat area.

 

That's J8 - unused in the 2015 Wrangler since it didn't come with power seats. I take it you are not the original owner? That's tapped into the unused (and unfused?) feed for whatever purpose is at the end of that blue wire. Find the end of the wire to see what it is doing.

But that's not related to the ABS issues you are having.

The ABS fuses are J6 and J7.

U0121-Lost Communication With Anti-Lock Brake System (ABS) Control Module. It can be set by several sources, including the ORC, ESM, PCM, SCM, TPM, TIPM, TCM, and ASBS. That means is a rather generic DTC that can be set by every module that communicates with the ABS. I think you are on the right track to check the fuses first.

Here is a list of possible causes from the Chilton manual. Good luck!Possible Causes

CAN BUS CIRCUITS OPEN OR SHORTED

ABS MODULE

DTCS RELATED TO BATTERY VOLTAGE, IGNITION, OR VIN MESSAGES

TOTALLY INTEGRATED POWER MODULE POWER AND GROUND

TIPM NOT CONFIGURED CORRECTLY

TOTALLY INTEGRATED POWER MODULE (TIPM)

MODULE THAT SET THIS DTC