Technical C121529 error brake light switch

[Grumpa1]

Have a fiat ducato 9 speed automatic. The error relates to Brake light switch yet I’ve already fitted a new one . Someone said it may be a problem with the earth , does anyone know where the earth are . Cheers

 

[the green vanper]

I'd suggest adding more info about the van. Model, year, engine... We can assume it's a x290... But it would be better to be sure.

It'd be also nice to say 'hello' in the greetings section

 

[Grumpa1]

I'd suggest adding more info about the van. Model, year, engine... We can assume it's a x290... But it would be better to be sure.

It'd be also nice to say 'hello' in the greetings section

Hi thanks for the response, the vehicle I have is KNAUS Motorhome 2020 model year, 2.3 160bhp if that’s any help.

I’m a bit new to this forum game and being a bit of an oldie can’t find the greeting section so please don’t think I’m an old grumpa as my name suggests

 

[Communicator]

Hi thanks for the response, the vehicle I have is KNAUS Motorhome 2020 model year, 2.3 160bhp if that’s any help.

I’m a bit new to this forum game and being a bit of an oldie can’t find the greeting section so please don’t think I’m an old grumpa as my name suggests

Don't take any notice of him. He's just a relative, but keen, newbie on here. I never posted in the Newbie section, just added my post where I knew that I could help. The main things with a forum is to be precise, and to post the eventual outcome, even if we have not been able to help directly. Your response could help others in the future.

Base vehicle model is the most important yours will be an x290, as indicated by the first 3 numbers of the VIN., which will probably have the form ZFA290.........

Regarding your problem, are all the brake lights, including high level, working ? As your vehicle is a MH, presumably on an Alko chassis, the lights at the rear, and wiring will part of the conversion. I would expect to find a junction box hidden somewhere underneath.

 

[theoneandonly]

Dont be surprised if the vin number starts with zfa250 not 290.
If its an Alko chassis then ?
If its a fiat special mh chassis (lower and wide at rear painted fiat white not galv) as mine is then the Fiat loom comes to a junction box just before end of chassis. This used by towbar providers as a tee point, mine is on nearside.(Rapido). You would find an earth return here.

 

[Grumpa1]

Dont be surprised if the vin number starts with zfa250 not 290.
If its an Alko chassis then ?
If its a fiat special mh chassis (lower and wide at rear painted fiat white not galv) as mine is then the Fiat loom comes to a junction box just before end of chassis. This used by towbar providers as a tee point, mine is on nearside.(Rapido). You would find an earth return here.

Yeah the chassis is ZFA250. It is the fiat chassis not the Alko, I found an earth connection just above the throttle pedal which was not fully tightened, tightened and checked continuity all good, road tested all appeared ok until on a downward hill into my estate weaving between parked cars then warning came on checked fault codes to find additional code P085786 active and the old C121529 stored. I’ve not seen or checked for the rear light junction box so will have a look over the weekend and post my findings.

 

[theoneandonly]

Not sure what your code actual is hers 2 guesses

P0857​

Traction Control Input Signal Range/Performance​

P0860​

Gear Shift Module Communication Circuit​

 

[Grumpa1]

Not sure what your code actual is hers 2 guesses

P0857​

Traction Control Input Signal Range/Performance​

P0860​

Gear Shift Module Communication Circuit​

Thanks for reply, been and had a chat with one of my old buddies who’s is now a Fiat mechanic, he gave me instructions on how to reset the brake light switch from a 2015 Fiat bulletin ( Ducato 290 brake pedal switch DTC C1215 ) it resets the internal switch position. Take hold of the switch turn clockwise by 45 degrees until it stops then back 45 degrees until it locks into position. This sets the switch rod length to the brake pedal. Not sure if the ignition needs to be on so I’ll try it first without and road test.

 

[Grumpa1]

Not sure what your code actual is hers 2 guesses

P0857​

Traction Control Input Signal Range/Performance​

P0860​

Gear Shift Module Communication Circuit​

Thanks for reply, been and had a chat with one of my old buddies who’s a Fiat mechanic now and he gave me

Thanks for reply, been and had a chat with one of my old buddies who’s is now a Fiat mechanic, he gave me instructions on how to reset the brake light switch from a 2015 Fiat bulletin ( Ducato 290 brake pedal switch DTC C1215 ) it resets the internal switch position. Take hold of the switch turn clockwise by 45 degrees until it stops then back 45 degrees until it locks into position. This sets the switch rod length to the brake pedal. Not sure if the ignition needs to be on so I’ll try it first without and road test.

Hi all just an update on my brake switch and fault code saga, I carried out the suggested Fiat bulletin procedure on the brake switch as earlier mentioned then cleared all fault codes and carried out a good road test, motorways, urban and country lanes etc and all appears good so a simple fix after all. Thanks for all your help and hope this helps other members. Looking forward to more chats in the future and hopefully helping with members issues