bf mkII fault U0121

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bf mkII fault U0121

Postby VX L67 Getrag » Sun Jul 21, 2019 9:30 am

Hi all,

I just picked up a cheap 10/06 falcon sedan with zf 6sp auto & has no other fault codes in engine or abs but in the trans controller it has U0121 (lost communication with abs) & it has no speedo because of this I’m assuming & put it in limp mode!

I’m wondering if anyone else has come across this & may have an idea of what to look at?

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Re: bf mkII fault U0121

Postby VX L67 Getrag » Sun Jul 21, 2019 11:47 am

F9420DEF-1442-4F13-8128-137578DC4D73.png
F9420DEF-1442-4F13-8128-137578DC4D73.png (293.61 KiB) Viewed 651 times

According to a quick google it should be fairly simple, but wiring all looks normal...

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Re: bf mkII fault U0121

Postby 80gus » Sun Jul 21, 2019 9:05 pm

I've had this before swapped speed in from abs to tcs, and disabled vid and it fixed it, was a FG tho.

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Re: bf mkII fault U0121

Postby VX L67 Getrag » Sun Jul 21, 2019 9:15 pm

Thanks for the info, I’ll try it out!

I’ve asked someone else who’s dealt with these more often but no response so I’ll keep everyone updated!

Thanks again

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Re: bf mkII fault U0121

Postby VX L67 Getrag » Mon Jul 22, 2019 11:00 am

So a bit of an update...

When all faults are cleared & reset the speedo works until it gets to about 40kmh then warning light's flash on dash & speedo cuts out & then everytime it gets to around 40kmh the TCS & ABS & skid lights all flash on.

The other strange thing is although the speedo doesn't work it still clicks over trip metre/odometre but I don't think it's correct as it normally smack on 30kmh drive to work & think it only registered 20kmh.

So I tried swapping speedo source & disable VID but that stops the speedo from even working for that first bit, strange thing with the BF it's set by factory for TCS so I changed it to ABS... the other option there is OSS but I'm not sure what that is & can only assume maybe speed sensor on G/box but I don't think the ZF's have them.

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Re: bf mkII fault U0121

Postby 80gus » Mon Jul 22, 2019 6:04 pm

OSS is a digital speed reference for B series only, via pin B7 on the ecu.

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Re: bf mkII fault U0121

Postby 80gus » Mon Jul 22, 2019 6:08 pm

VX L67 Getrag wrote:So a bit of an update...



So I tried swapping speedo source & disable VID but that stops the speedo from even working for that first bit, strange thing with the BF it's set by factory for TCS so I changed it to ABS... the other option there is OSS but I'm not sure what that is & can only assume maybe speed sensor on G/box but I don't think the ZF's have them.



PCMtec gives more options. but sounds like there is a genuine issue, try a ABS module reset with forscan or similar.

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Re: bf mkII fault U0121

Postby VX L67 Getrag » Mon Jul 22, 2019 11:18 pm

Yeah I think it’s a hardware issue & 99% sure it’s in the abs, I might change vas source back & leave vid disabled.

I don’t have forscan with activation but strange thing is I used my Gscan with latest updates to delete ALL faults & couldn’t remove abs communication issue, but forscan free version did straight away!

So many tools workshop’s need to do various models!

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Re: bf mkII fault U0121

Postby VX L67 Getrag » Tue Jul 23, 2019 9:44 pm

I'm starting to think "maybe" the disable VID in HPtuners helped & thats why FORScan could clear faults but the Gscan couldn't.. time will tell!

I enabled the FORScan for the free period & hopefully it will help with finding issues as I think it may be a module replaced with mismatch, but as I haven't used it before it will take a bit of playing with to figure out each section.

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Re: bf mkII fault U0121

Postby VX L67 Getrag » Tue Jul 30, 2019 10:31 am

Has anyone got a BF MkII sedan with ZF 6speed that they can get a screenshot of the abs module info, I changed mine & didn't keep a backup of what it was before I changed it but it now say's invalid....
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my bf sedan(ABS Module Config-AS BUILT format).png
my bf sedan(ABS Module Config-AS BUILT format).png (59.29 KiB) Viewed 450 times
my bf sedan(ABS Module Config).png
my bf sedan(ABS Module Config).png (54.64 KiB) Viewed 450 times

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