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Thread: 07 Mazda 3 Dreaded U- 121 and U155 codes after changing cabin air filter

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    Default 07 Mazda 3 Dreaded U- 121 and U155 codes after changing cabin air filter

    Hello guys,

    My 1st post here!!!

    Just wanna know how am I getting a CAN BUS U 121 and U155 codes after chaging my cabin air filter. for those of you who have changed this cabin filter, know how ^#$#%$ of a job this is. I made sure all connectors go in proper place. After, I got these codes, I drove the car around the block but found nothing... However, I am afraid of this thing stalling on me on the freeway. U121 is CAN communication lost to ABS module and U 155 is CAN communication lost to instrumentation cluster. The cluster works fine as I see the needles moving ... ABS.. I don't have the correct road conditions ( and balls ) to test it out..

    Any advise is appreciated

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    Default Re: 07 Mazda 3 Dreaded U- 121 and U155 codes after changing cabin air filter

    Did you disconnect the battery before you took everything apart?

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    Default Re: 07 Mazda 3 Dreaded U- 121 and U155 codes after changing cabin air filter

    Quote Originally Posted by jeff7670 View Post
    Did you disconnect the battery before you took everything apart?
    Nope... and there in lies the problem may be... I suppose, while removing the connectors, I may have shorted some thing causing the loss in CAN commmnunication, prompting the ECU to flash the check engine light... I put all the connectors back and erased the codes... Then drove the car for 50 miles... nothing yet... Let's hope it stays this way...

    What a B! ch of a job to change this filter man!

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    Default Re: 07 Mazda 3 Dreaded U- 121 and U155 codes after changing cabin air filter

    Ya lets hope for sure. I think Mazda first designed the cabin filter and then the entire car around it.

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    Sr Member RedRaptor's Avatar
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    Default Re: 07 Mazda 3 Dreaded U- 121 and U155 codes after changing cabin air filter

    In my almost 15 years of ownership, I have never attempted to change the cabin air filter myself. This is exactly why.

    Bring the car into Jimmy @ StreetPerformance. Let's see if he help you resolve by putting all the connections in place.

    I change my filter every 24 months and Jimmy has never failed to do it properly.

    Good luck!
    2004 Mazda3 Sport GT|Winning Blue| OG 2.3L @ 420,000 km

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    Member Ogata's Avatar
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    Default Re: 07 Mazda 3 Dreaded U- 121 and U155 codes after changing cabin air filter

    Quote Originally Posted by RedRaptor View Post
    In my almost 15 years of ownership, I have never attempted to change the cabin air filter myself. This is exactly why.

    Bring the car into Jimmy @ StreetPerformance. Let's see if he help you resolve by putting all the connections in place.

    I change my filter every 24 months and Jimmy has never failed to do it properly.

    Good luck!
    +1 He does mine with no hassle and does it like a breeze..just pay the good man his labor
    2008.5 Metropolitan Grey Mica Mazda 3 GT Hatch with Luxury Package DONE: OEM LED Side Mirror Turn Signals | TM3 Decals / Plates | Axela Badge | 3M Scotchguard Film on Front Hood / Fenders | Solarguard Quantum Tints 37% Front 28% Back | Flipkey | JDM Rainguards | MS3 Rear Valence | Super White LED Interior / Trunk / License Plate Lights | Smoked LED Sidermarkers | Powdercoated Blue 18" OZ Ultraleggera Rims | Michelin Pilot Sport AS3 | Blue Calipers with Gunmetal Axela Decals | HID 6000K/3000K with Yellow Film Fogs | Hella Tones | Rally Armor Mudflaps | Powdercoated Gunmetal Xenon Expert Aluminum Pedals | Clear Reflectors | Carbon Fibre Rear Emblem Insert | Redline Elite Hood Lifts | Cross Drilled Rotors with Hawk HPS Pads | CP-E Tow Plate | Her: 2012 Sky Blue Mica Mazda 3 GS

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    Jr Member G ~ MINI's Avatar
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    Default Re: 07 Mazda 3 Dreaded U- 121 and U155 codes after changing cabin air filter

    2012 Mazda 3 GX
    Not sure if its wired different.
    I've changed the cabin 5 times in 7 years
    and never disconnected the battery and
    never had an issue.

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    Member Ogata's Avatar
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    Default Re: 07 Mazda 3 Dreaded U- 121 and U155 codes after changing cabin air filter

    Quote Originally Posted by G ~ MINI View Post
    2012 Mazda 3 GX
    Not sure if its wired different.
    I've changed the cabin 5 times in 7 years
    and never disconnected the battery and
    never had an issue.
    2nd gen is easier..i too have done it on my wife's 2012 with no issues.. its the 1st gen (like mine) where the fuse box is in the way.

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    Default Re: 07 Mazda 3 Dreaded U- 121 and U155 codes after changing cabin air filter

    Thanks !! ...This grasshopper has learned something new

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    Default Re: 07 Mazda 3 Dreaded U- 121 and U155 codes after changing cabin air filter

    Its really not that hard, just don't forget to unhook the battery.

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