Hi Guys,

Really need your help with diagnostics on this one. I'll try to keep it as brief as possible.

I have a fiat punto GT 1998. About two years ago my key code light kept coming on and the car wouldnt start as a result. This was resolved when I disconnected the battery. After a few months the code light then remained on and I couldnt start the car and couldnt use it for months. I tried to get the ECU uncoded but after speaking to 3 different companies they couldnt do these type of GT punto.

After much research and help from fiat forum, I managed to get a new ECU with the code box, key and barrel. Fitted it in myself and it worked!

Few years on and the key code light goes on/off while stationary. Car now sometimes starts and doesnt. If I leave the car for a while, light goes off and starts. But if I turn off the engine and try again, it doesn't. Funny thing is that when I try to start the car with the clutch down and in gear, when trying to move and stall the car, it sometimes starts. This helps the key code light go off and it then ignites.

I have also changed the coil because I was advised it could be that, but same problem.

Any ideas?? Do you think it could be the ECU again, what could be causing the problem. I was told it could be some intermittent problem or something to do with the relay.

CooL-A

well first have a look at the fuses and condition of the fuse holders

then you need to check the plugs to the engine ecu and code box have full battery live and a good earth not sure of the pins or colours right now but black and red is a good start

measure the battery first

then measure the terminals

if you seen no significant drop in the voltage under no load

you then need to test it under load

to do this on the live side you set your test meter to volts again put one probe on the battery live and one on the live wire you want to test like the code box for example would be a good start then turn on the ignition

you should not see more than half a volt drop over the live circuit from battery to code box

if there is a voltage drop shown on the test meter then there is resistance in that wire somewhere

the same can be done for the earth wire

first you need to test the earth from battery to shell of the vehicle is good under load ie lights and stuff switched on

then when you know the shell has a good earth you can test from earth pins out of ecu's to the shell around you using door catches and any other exposed metal

once your sure everything has good power and earth you need to take a look at the signal wire from the code box to engine ecu

and also look into checking the resistance of the aerial around the ignition switch and comparing to manufacturers specks

other than that there aint really allot to the code system

the relay you have been warned about is located under the plastic cover on the back of the bulkhead it's white in colour and about twice the size of your average relay

as it all started working again when you swapped the ec'us and then packed in i'm guessing wiring is at fault as doing this would not affect the relay

how ether you will have moved the wires for engine ecu code box and aerial in the process so i suggest you start with those

other things to check are the engine earth is secure i think the engine ecu has a dedicated earth to battery but not sure and it's worth a check

same again test meter set to volts probes from battery earth to engine and crank wile watching the meter again shouldnt see more than half a volt drop

Thanks for your help - Much appreciated

I'll have a go at it.

CooL-A

BTW - does anyone know if its possible to bypass the code system on this type of punto so it doesn't matter if the key code light is on or not??

CooL-A

CooL-A said:

You responded to my post a while ago. I checked some of the electrics and they seem to be fine. Most people are advising its the ecu or key and to change the whole system.

I found a few people who are selling their ECU with key, key barrel and codebox. One is a M reg, P reg and the other R. My car is a 98 S reg, do you think the R reg is more appropriate? Reason why I'm asking coz its a bit more expensive.

This would be the second time I changed the ecu system, but the 2nd one I did by from a breaker. Can these ECUs really play up that many times?

Funny thing is that when I crank the car and restart, code goes off and sometimes it works or if I dont drive for a day or so. I'm not sure what to do now, so I'm hoping changing the code system again will work.

Thanks,

CooL-A

Click to expand...

if someone advises you that something is faulty ask them exactly how they know this if they can't give you a straight answer they don't know what is wrong simple as that

there is no way to bypass it yourself how ether some firms will do you coded and uncode chips to fit in the ecu normally some sort of tuning chips but i only know this is posible for 1.1 1.2 not sure if they will do turbo ones you would have to ask on the forum

how ether as you have already tried one set on the car i should think it's highly unlikely they both suffer a fault let alone exactly the same fault also taking in to account that a high percentage of code system faults are wiring related not ecu's as they are normally very reliable if used properly

you need to run a few simple tests on the car with a test meter available for 5 pounds at local shops

the code box has a permanent live and a switched live an earth a signal wire and a wire to the light in one multi plug the second plug simply goes to the arial around the key

the pins are numbered if you look closely on the code box

so

check battery voltage first so you know what you should be getting at the code box

check that the battery has at least 12.4 volts preferable more

remember a fully charged battery should rear 12.76 a half charged battery is 12.4 not a big difference

the first multi plug contains 8 pins total

pin 4 earth black should be a good circuit to earth more than half a volt drop under load is a bad earth

pin 3 permanent live red from battery through 30 amp fuse under bonnet to check then a 7.5 amp fuse in the interior fuse box to check and then to code box this should be battery voltage and no less

pin 2 earth path for code light through code box white and blue the code light is powered from ignition switch in both (ign) and (avv) positions and the code box earth's it to illuminate or extinguish it this is not important as you know it works and does not affect the code system even if it was broken anyway otherwise a blown bulb in the dash would immobilise the car

pin 8 ignition switched live orange should be powered in both (ign) and (avv) positions must be battery voltage no less

pin 6 signal wire to engine ecu grey green this goes to pin 13 on the engine ecu same colour so check for continuity

pins 1 5 and 7 unused

second multi plug contains 3 pins 1 and 2 are both the aerial around ignition barrel check that this is not open circuit or shorted it should be 45 ohms

pin 2 is unused

check that the orange wire on the back of the ignition switch is live in both the (ign) and (avv)

if all this is correct then you need to make sure the engine ecu has a good live and earth feed i would have to look to find the pin numbers for the gt i don't have them right now but i'm sure you have enough to check there

the most common failures on the puntos are the ignition relay under the bonnet big white one under the cover on the bulkhead

this would cause symptoms of engine ecu or code box faults

so if you wana replace anything try that there about 24 quid from the dealer and not really available anywhere else there quite common to many fiats like punto bravo brava merea seicento so easy to find in the scrap yards

i wouldn't advise wasting your money on another entire system before checking everything first

if you do want to then go for the r reg as this is the same engine remember there are a few different variations on the engines over the years

i may have asked you already but i need to know a few things from you

are you using a red key or blue key on the current system fitted to the car if it's blue is it a fiat key or does it have a diferent brand name on it

turn it twice in the ignition and tell me what happens to the code light does the light come on and go out both times or does it tay on the second time and so on

only turn it to ign not crank/avv

can you here the fuel pump running when you turn the ignition on both when it's working and when it wont start

hum ok keep turning it on nd off and see if the code light stays on every second time you turn it on

the code light should stay on after turning on the key for just 0.7 of a second then go off

the ignition relay looks like a normal relay only it's 2 relays in one and about twice the size has a multi pin connector on the bottom and is housed under the plastic cover at the back of the engine bay held in place with 2 x head screws it's white in colour and held in place with a 10mm nut

the bulkhead is the piece between the pasenger compartment and the engine bay

just out of intrest were a bouts do you live i would be happy to take a look if you could get it to me

Hi ! I have a 2000 Fiat Punto 1.2 SX,and about 1 year ago while i was driving the engine suddenly stopped and started again only after 15 minutes.
From then the car continued to stop more and more often.Every time when it stopped the key code appeared on the dashboard.What is funny is that the engine stoppes when the clutch is not into any gear.All these stoppes, until 2 weeks ago when the car refused to start ever again.I went to a local service and they told me that the Immobiliser(code box) is damaged.So i bought from a guy the hole package: ECU,code box,barrel and a key. All these were mounted on the car.But surprise! the car now starts but the same problem the engine stoppes after a while of driving.No one from the service couldn't tell what is exactly the problem.I've searched on forums in my country (Romania) and seems that nobody can't tell me nothing.I think in other countryes some people know what is the problem.Can anyone help me I would appreciate very much