Code U0121

[Chris20]

Had a friend mechanic put his scanner on my Jeep and code U0121 came up.

According to his scanner it is a ABS module communication problem. One of his suggestions as to the cause was that there is a cable going from the battery back to a Anderson plug and the cable is secured to the wiring by a couple of zip ties. He says that there maybe causing a conflict. He did give it a technical term which I can't remember. In his reasoning he said that there is no sheilding in the ABS wiring or the 12v power cable.

Can anyone advise where to start to rectify this problem.

I had a resistor in the swirl motor circuit but put it back to factory settings before the scan. The TCL light was still happening occaisionally with the resistor in and then the vehicle went into limp mode.
Advice apprecciated.
Chris

[Clarky]

The fault code means that the ABS module isn't communicating with the Front Control Module via the CAN-BUS. This can be triggered by low battery voltage, bad earth or even bad contact within the connecting plugs.

Not a jeep diagnostic document but the same principles apply


This is how the jeep CAN-BUS is connected.


What you need is a diagnostic tool that can run an ABS test. If the test won't run then its a wiring issue or bad connection. If the test runs & fails I would be thinking the ABS module is the culprit.

[ren0vator]

Originally Posted by Clarky

This is how the jeep CAN-BUS is connected.

Too many acronym's for me
Can I buy a vowel
Start by checking the ABS fuse

[Chris20]

Thanks for the replies. Appreciated.
I have checked the fuse F4 30amp Pink.
Is this the correct one or is it #25 in the fuse compartment under the steering wheel?

Thanks again for your time and effort.

Chris

[ren0vator]

There's three fuses listed:


Under the bonnet:
4 and 21 in the rear fuse box (power distribution centre)
Under the steering wheel:
25 in the lower fuse panel (junction block)

[Chris20]

Thanks for the fuse information ren0vator.
I have checked these fuses and are all ok.
Now I am thinking the module could be the culprit.
Is there a way of checking this, with a scanner I presume.?

Thanks for your time and effort.

Chris

[Clarky]

An advanced OBD2 programmer like AutoEnginuity can run tests and determine if the ABS module is operating correctly but only if it can communicate with it in the first place. If there is a BUS issue it won't talk to the ABS module.