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U0121 what does it mean ?

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It means that the engine computer has lost communication with the antilock brake controller (CAB) check the wiring. Disconnect the ABS module pigtail and inspect the pins. Look at wiring near the battery and see if acid has caused corrosion

Posted on May 17, 2014


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Posted on Jan 02, 2017


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Whats the answer for U1120 engine diagnostic on 2008 Chrysler Aspen?

Lizzie, U1120 means the PCM doesn't receive a vehicle speed signal from the Anti-lock brake Module over the CAN C bus. You may have to have a good tech. diagnose and estimate repair. Check the attached links,instruction and guides, Good luck
"I hope this helped you out, if so let me know by pressing the helpful button. Check out some of my other posts if you need more tips and info."
U1120 Engine Diagnostic Code For 2008 Chrysler Aspen
Error Code U1110 and U1120 Chrysler Forum Chrysler Enthusiast Forums
HELP Codes U1120 U0121

Aug 11, 2016 | Chrysler Cars & Trucks

2 Answers

Code u0121 please how do i fix it

year 2000? not really huh?
seems the year is wrong,
so if that is true ,is car wrong too, JEEP and grand cherroke wrong too?
for example the 2011 Compass / Patroit
2011 (tsb to replace Pcm) ( have TSB, google finds it easy)

1: get it serviced yet?
2: read the FSM WJ book yet, do all tests it tells you to do ?
there are only 2 paths.
they do it , you do it.?
which one?

WJ 00 (dead end, no code there, OP posted wrong year,. )

U codes are specific to specific jeeps. and years.
posting wrong car....
makes answers impossible. did you scan it yet?

but one thing, we do , is check fuses first.
if the ABS module does not talk, if in fact it is ABS code.
and scan it, first. too.
fuses then scan.
or fail.

these are factory codes, not usa federal codes like P-0300
so post full car spec, and engine, type for best answers.
lets say car is a 2005 GC.
and U0121
see chapter 8E-72 in fsm tells you what to do,
if car is 3rd gen jeep GC, then it has this buss.
the below is the buss, the can c bus
the code means PCM cant talk to the ABS box.
id be all over fuses. and resetting them all.


Jul 13, 2015 | 2000 Jeep Grand Cherokee Laredo

1 Answer

05 chrysler 300 code u1120 and u0121

Both of these have to do with the ABS system. U codes are lost communications codes from computers. Sometimes they are the wires. When you have different computers not communicating. Since yours are both from the ABS, I suspect the ABS module has died. Still could be the wire though (not likely). Check the wire for resistance. if good( less than 5 ohms) then the module has died. When you have ABS system malfunctions, the brakes revert back to the old system. Meaning if you hit the brakes to hard, they could lock the tires and have a skidding effect. BUT the brakes still work, they will stop the vehicle. Basically it is your call to have them fixed.

Nov 09, 2014 | 2005 Chrysler 300

1 Answer

What does code "u1120" and "u0121" mean?

Throttle Position Sensor/Switch A Circuit Range/
Performance Problem. P1120 Throttle position sensor out of range
P1121. clean throttle body out good, this may fix problem. if not replace or adjust throttle position sensor. Good-Day!

May 17, 2014 | 2005 Dodge Dakota Quad

1 Answer

DTC U0121 - Lost Communication With Anti-Lock Brake System (ABS) Control Module

If you clear the code does it come right back AND is the ABS light illuminated on dash?

Apr 17, 2014 | 2011 Ford Ranger

1 Answer

Hello, I have a problem with my Saturn Astra 2008,

U0121 Lost Communication With Electronic Brake Control Module

As with most trouble codes, the U0121 code gives a general diagnosis. Review the info on this link. Look through the service bulletins. The problem could be a loose plug or faulty wiring to one of the modules or between modules that are listed in the article. I hope this helps somewhat. Good Luck......

Apr 03, 2014 | Saturn Astra Cars & Trucks

1 Answer


Hi there:
DTC U0121 - Lost Communication With Anti-Lock Brake System (ABS) Control Module

If the fault come back again, this is being caused by a failed ABS module. You will need to replace the module and run the verification process to correct your concern. To run the verification process you will need access to a full level scan tool (as factory scan).

Hope this helps; also keep in mind that your feedback is important and I`ll appreciate your time and consideration if you leave some testimonial comment about this answer.

Thank you for using FixYa, have a nice day.

Jul 03, 2012 | 2005 Jeep Grand Cherokee

1 Answer

U0121 code

Usually a P0121 is a problem with the throttle position sensor.
A mechanic would use a scanner to check the output.
You can also use a VOM and check resistance.

Jun 29, 2012 | 2005 Jeep Grand Cherokee

1 Answer

What do codes: C1223, U0121, U0123, U0124, U0126 mean found after a diagnostic test in my 2004 Toyota Solara?

Same here. I stopped by Autozone and they gave me the following codes. P0020, U0126, U0124, U0123, U0073, C1223 and C1201. The only thing I did was splash some fuel the day before at a questionable gas station. Please help

Jun 19, 2012 | 2004 Toyota Solara

1 Answer

Emission test found some trouble codes

U0121 Communication error to ABS HU/CM

Apr 06, 2009 | 2005 Mazda 6

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