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Discussion Starter · #1 ·
Tuesday I was driving around wit my family cuz is running good, get to they'll turn the car off of course later when we come back to the car I start it and my check engine light and the brake, abs, and bas/ESP light comes on and I put the car in drive an the car isn't going anywhere it's in limp mode, put it back in park and turn it off to see if the lights go away so then I start the car again and the lights disappear but the check engine light stays on but the car runs fine, so later that day I do the key dance and it give me U0121 and I have no idea what it is but I wanna fix it rite away so I take it to autozone an they erase the code after I leave the car runs fine engine light still off, when I get home I turn off the car and I go in and my family and I left and I start the car up again and the all 4 lights come on again so I do the key dance and I get the same code what can I do cuz I hate having the engine light on


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U0121 means the PCM lost communication With ABS Module.

The PCM isn't receiving a consistent signal from the Anti-lock brake Module over the CAN C bus. This can be caused by the ABS module, PCM or something wrong with the can bus. This might be just an erroneous code and may never set again.

Since it has set the code twice now would be a good time to get it to a dealer for a full diagnostic because only the dealer's scan tool can individually query each individual module involved.
 

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Discussion Starter · #3 ·
Yea maddog I was thinking the same, I won't be able to take my car till Monday or Tuesday cuz I work the rest of the week but hopefully they can tell me what it needs, just like anyone else it bugs me a lot to see the check engine light on


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Yes, always return the car to stock tune before you take it in to the dealer, especially for those times they are going to scan the PCM.
 

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Discussion Starter · #11 ·
Yea it came back so I made an appointment on Tuesday wit Chrysler they're gonna charge me 90 just to run the tests to see what it can be and we'll take it from there I hope it's nothing major but thanks for the response maddog, btw how's ur build coming out???


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Discussion Starter · #13 ·
Took my car to the dealer and they diagnosed it and said that the abs module is no bueno so Monday ill be taking it back or sooner to get it fixed and they're gonna charge me 862 for parts and labor


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I disabled the security module from my ecu(its reset and if i plug in skim module) it will overwrite my ECU back to wrong security... I removed the skim module from the car.... My key starts the car fine

I have this message but I think ive had it for a long time. Its an engine swap (v6 to v8). The car runs fine though, This sets the dash off though... abs, bas, ebs.

Parking brake is off.

I assume this is the Key doesnt match issue?
 
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