ok i seem to have a weird problem, discussion started on this thread https://www.fiatforum.com/punto/284062-mk2-punto-rh-footwell-ground-location.html but the title is not adequate anymore..

My car is a mk2 punto 1.9D, it will idle for hours but after about 10mins of driving it blows the F3 MAXI fuse (ignition switch)..

there seems to be no pattern to it and can't replicate it with the car still.. can't find any short in the wiring and everything works fine with the car standing still..

a day before the problem showed up i began getting static on the radio with the engine on and the airbag light came on, expected it to be a bad earth somewhere but think it's related..

alternator and battery are around 1 year old, both tested out fine with a load test..

i though of the steering but then noticed it's on a separate fuse, have no ideia what else is used while driving that doesn't affect the car standing..

out of ideias..

since i couldn't track the problem and everything tested out fine i used a different tactic on this one, got 20 20amp maxi fuses in the glovebox and kept driving.. odd enough i got 150km out of it before it blew another fuse 30mins ago, was still waiting for the plugs to warm when it happened.. replaced fuse and got about 10meters before i started to smell a short, stopped the engine and finally saw the smoke..

fuse didn't blow and i still drove the 20km home without hassle, everything seems to work and there is no more static on the radio... still disconnected the battery in case something might go wrong during the night

tomorrow i'll disassemble the area i saw the smoke and look for evidence of the short.. the smoke came clearly from under the steering, can't see anything obvious from the fusebox though....

i cant help you but look forward to hearing the result
ive certainly had ignition switches going into melt down on vauxhalls and know of a cavalier and a corsa that burned themselves out because of this problem

I would isolate the ign switch and check continuity/resistance between the ign switch pos feed and ground with the key in the run position. Radio interference is a cct making and breaking somewhere and the ign switch looks a likely culprit. Twist the key back and forth a bit with the motor running.
Be careful - wires when heated up can suddenly ignite and fill the cabin with eye burning choking toxic fumes in seconds.
You don't have a heavy key bunch by any chance ? Have seen them wear out a switch and run the starter motor from pos 1.

s and b said:

i cant help you but look forward to hearing the result
ive certainly had ignition switches going into melt down on vauxhalls and know of a cavalier and a corsa that burned themselves out because of this problem

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I always try to post a conclusion in my topics even if no one replies, that way if someone else gets a similar problem they should know where to start looking..

Brendan W said:

I would isolate the ign switch and check continuity/resistance between the ign switch pos feed and ground with the key in the run position. Radio interference is a cct making and breaking somewhere and the ign switch looks a likely culprit. Twist the key back and forth a bit with the motor running.
Be careful - wires when heated up can suddenly ignite and fill the cabin with eye burning choking toxic fumes in seconds.
You don't have a heavy key bunch by any chance ? Have seen them wear out a switch and run the starter motor from pos 1.

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the mk2 punto ignition switch only has positive voltage going through it, unless it's found a way to short directly to something else it shouldn't cause a short...

the radio static was the tipical alternator whine since the pitch was following the revs and only afected a few stations, one of which is the station i always listen to so i noticed right away something was wrong...

my thinking is if it shorted four times and passed enough current to blow a 20A maxi fuse it should have left a very visible mark, maxi fuses are not that easy to blow..

i'm one of those minimalistic people, car key is alone with only a ring on it, keychain broke and i never bothered to get another on


i'll know it soon enough, i'm taking it apart in about an hour.

took it apart this afternoon, can't see anything obvious.. no burn marks anywhere, the plugs are white and look brand new...

after getting everything together and driving for about an hour i got some more smoke (barelly visible) and the burning smell, but no tools meant a quick look through the fuse box and keep going.. no fuse blew..

seems to be no pattern to when it occurs and i don't like the ideia of driving with the plastics removed since it could encourage some idiot to break the window thinking he could hot wire the car...

i hate intermittent problems


EDIT: reversing light is now on every time i turn the key, people had been telling me the ligh was on but when i checked it was always off..

problem solved.


so now the fuse would blow when reverse was engaged and key on (even with engine off)... dead short is easy to diagnose..

looking at the interior fuse box it looked clear the reverse light fuse was passing excessive current since it was melted but not blowing..

then noticed the carnage... a wire had melted the insulation from the interior fuse box brown plug to the engine fuse box brown plug, then another wire from there down..

removed front bumper and left headlight to trace the wire and spotted the problem right away.. both wires from the reverse switch were shorting directly to the chassis from the loom rubbing under the headlight..

now i just need to replace the wires and redo about 2m of loom..

will try and get some pictures tomorrow..

thanks for the update
sounds like a one off then?
pictures would be velly interestling

that section of loom runs across the front of the car and the plastic tubing holding the loom has rubbed in both corners under the headlights, only the left hand side had rubbed far enough to short the wires... so it could be a one off or it may begin to happen has the car ages.. i do a lot of mileage (500k+ a week) and most of it is on degraded streets, that could be one of the cause..

i had a random Wire burn out on me too/Rub to shreads
Again in the stupid Black plastic stuff you mentioned!

took me a while to figure it out -- but Either replace or rejoin it and insulating it very well

Could always put some duck tape on the part it rubbed most - try and slow it down again?

Ziggy

no pictures yet, left the camera at the shop...

i had to replace 4m of wire, 2m green and 2m blue.. it had melted the insulation along the whole lenght, actually made it very easy to trace.. direct shorts are easy to trace, but intermittent like mine was before are a pain since it's hard to replicate..


now i have a new problem, went to turn off the airbag light and no airbag ecu detected, even fiatecuscan can´t detect it..

so next week got to figure that one out, fuse is good, replaced it with no effect.. now i have to get the centre console apart and check if there's voltage at the ecu...

If FES can't pick it up - then there is probably a wiring problem between airbag ecu / Can Bus system?

Hence why Airbag light is on?

Ziggy

been re-reading some stuff i have on the punto and noticed the part where the airbag uses pin 3..

i wonder if the diagnostic unit used does that, it was a Bosch kts570.. since the vag-com cable was original and unmodified i think that was the reason FES couldn't connect to it either..

the airbag ecu was actually dead, that would be the reason diagnostics didn't work

smokeme said:

the airbag ecu was actually dead, that would be the reason diagnostics didn't work

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Thats rare.... What killed it? Power Spike / Shortage
Water?

Since big fuse's popped - i bet its spikes that have done it

ziggy

not sure yet, i'll see tomorrow if i can find time to remove it and send it off for possile repair.. airbag diagnostic got no response so it is a confirmed dead ecu, it plugs directly to the ecu and rules out power or wiring problems..

if this ecu can't be repaired it will be a bit hard to find a replacement, it only has a drivers airbag, not even pretensioners are present, noticed this comparing the wiring diagrams to the wiring present on the ecu plug..

erm.....

I connect to the Airbag ECU via the Fusebox Diagnostic port....

Try that way - you MIGHT get it fault code for you then

Ziggy

neither the bosch kts570 diagnostic unit or FES could connect to the airbags through the diagnostic port (eobd socket), so someone who specialises in airbags was brought in and his machine connects directly to the airbag ecu socket and still got no connection, his experience says it usually means a dead ecu but it could just be locked up..

try leaving it disconnected overnight - it means leaving the battery off too


Also Check the pins on the input, there should be a 12v feed pin somewhere

Ziggy