F125 Misbehaving

David's8 · #1 3rd August 2022, 09:48 AM

I discovered a new (to me) mode of failure of the F125 which, fortunately, MJ was aware of. Whilst driving to Liverpool I stopped in a queue on the outer lane of a dual carriageway at some road works near Dumbarton. As i was there for some time, i switched off the ignition. Came to start and.... nothing. Some frantic action with the key and gearlever whilst traffic built up behind me and then it started.

Anyway, put it down to being in neutral/park or something and went on. We pulled in at Tebay for a break, ironically opposite the Tesla charging points in a quiet corner, but when it came to start nothing happened. All normal lights came on and relays clicking in the passenger footwell but no starter motor action. After 10mins called our breakdown cover (Nat West Flex plus who use the AA). Told it was about 2 hrs. When they arrived battery check showed all was OK. I wondered about the chassis earthing point so they jacked it up to check. I then took the liberty of phoning MJ (for which I apologise profusely again) and MJ said that she had had a similar issue and its either the relay in the footwell, dirty contacts at the connector next to the earthing point or the F125. After some discussion the AA guy changed the relay which made no difference, checked the connector (all good) but then managed to jump start shorting between the earthing point and the connector. So it pointed toward the F125. But then faced with that being the only way to start the car, I returned home.
Subsequent investigation a few days later and further discussion with MJ who talked me through the work-round which by-passes the relay which transmits the "I'm in "Park" " signal from the F125 which allows the starter to work. Basically, a short jumper between the terminals of the relay does the trick. The jumper is still in place whilst I figure out the way ahead with the F125,which given the cost of a fitting a new F125, might even be a permanent fixture!!
Anyway, many, many thanks to MJ without whom we would be all be a much worse place. (how do you know all this stuff, MJ??

)

HPsauce · #2 3rd August 2022, 10:25 AM

Exactly what happened to me a while back. I'll find the thread shortly....

December 2019! http://forum.a8parts.co.uk/showthread.php?t=15360

Quote:

Originally Posted by HPsauce

to bypass this relay I need to put my wire in the steel contacts (30 and 87 = 2 and 8), connecting the two thick red/black wires.

Didn't take a picture after doing it

, but David did.

My "temporary fix" lasted right through Covid until MJ replaced my F125 this summer.

HPsauce · #3 3rd August 2022, 12:23 PM

Quote:

Originally Posted by David's8

The jumper is still in place whilst I figure out the way ahead with the F125,which given the cost of a fitting a new F125, might even be a permanent fixture!!)

I thought about that but decided the failure MUST have been something broken inside the F125, so inevitably the risk of debris.
Given the construction of the F125 my view was that there's a significant risk of it affecting other circuits, so replace it sooner rather than later.

Later for me was well over 2 years, but for much of that it was on SORN due to Covid.

You need to get a slot in MJs diary, she's a dab hand at swapping F125s I believe.

strummagnet · #4 5th August 2022, 10:30 AM

There is a good write up in AudiPages describing the process:

http://www.audipages.com/Tech_Articl...chreplace.html

HPsauce · #5 5th August 2022, 10:36 AM

Indeed.

I printed all that and handed it to the garage that replaced mine a few years back. They did it all well inside a day without any drama.
Though the boss there used to work at Fontain (well-known Audi independent down South) and knew what was involved.

It was a brand new genuine one that was fitted, but it still failed after maybe 40,000 miles.

steamship · #6 5th August 2022, 09:21 PM

Quote:

Originally Posted by strummagnet

There is a good write up in AudiPages describing the process:

http://www.audipages.com/Tech_Articl...chreplace.html

That's the instructions I used when doing mine a few months back. My biggest problem was starting it at around 3:00pm and then getting eaten alive by midges around 7:00pm, so stopped for the night.

And yes, that 'one' bolt they mention is a PITA.

David's8 · #7 6th August 2022, 07:10 AM

Quote:

Originally Posted by strummagnet

There is a good write up in AudiPages describing the process:

http://www.audipages.com/Tech_Articl...chreplace.html

Yes,i have that in my maintenance file but it is PITA doing it on your back under ramps. Like HP, i might just save it up for another day when i have to get it up on a lift.

sarg · #8 13th May 2025, 10:11 AM

Seems I'm the latest victim of this issue, she let me down last night trying to get home from the gym, just had nothing from the engine at all, but plenty of battery juice.

Will be trying the interlock bypass this evening

HPsauce · #9 13th May 2025, 08:19 PM

Hope that gets you going!
As I posted in another thread mine started misbehaving and I had it replaced AGAIN quite recently with a cheap Chinese copy (with shorter cable!).
Same garage did it as before (in my village) and I gave them the Audipages tips PLUS MJs excellent extra advice. They were happy to fit a part I supplied.
And the mechanic managed to reroute the shorter cable without major problems. Overall not too many arms and legs at all!