U0121 ABS Module No Communication Code?

2010 FORD F-150

230,000 MILES • 5.4L • 4WD • AUTOMATIC

ERICH PETERSON

MEMBER
36 POSTS

Hi,
Getting a U0121 ABS no communication error code. I would like to check power and grounds at the ABS control module connector, and was looking for the connector pinout and wiring diagram.

Thanks!

Jun 28, 2026 at 12:54 PM

STRAILER

✓ASE Certified Mechanic
54,832 POSTS

Hello, U0121 means the other modules are not able to communicate with the ABS module. This can be caused by a bad ABS module, but more commonly you want to check the basics first: power, ground, fuse feed, and CAN communication wiring. Here is the wiring diagrams and pin out so you can do the testing needed to see what is going on. Check out the images (below). Let me know what you find.

Images (Click to enlarge)

Professional Diagram for 2CarPros Members
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Jun 28, 2026 at 5:58 PM

ERICH PETERSON

MEMBER
36 POSTS

Thanks so much. So, I checked all the powers and grounds and they all seemed fine. I reconnected the connector and the ABS lights went out! It appears to be the connector wasn't seating fully. Even when I insert it fully and press down on the lever, it still is able to come off. Not sure why this occuring.

Jun 28, 2026 at 11:35 PM

STRAILER

✓ASE Certified Mechanic
54,832 POSTS

Yep, sounds like a bad connection, check the pins and wiring at the connector, if okay and the code comes back I would replace the ABS module.

Jun 29, 2026 at 2:08 PM