I changed my car battery today (correctly!! I’m absolutely sure of that) and went to start the car and it only turned over and didn’t start. At this point I realised the electronic immobilser light and engine warning light remained on. At this point I would like to note the car has previously had the key lost and a key standard replacement (non-fiat official and not remote).

Is it possible that the ecu has forgotten the key code and needs reprogramming? Or does this sound like a fried ECU?

PrincessMegan said:

I changed my car battery today (correctly!! I’m absolutely sure of that) and went to start the car and it only turned over and didn’t start. At this point I realised the electronic immobilser light and engine warning light remained on. At this point I would like to note the car has previously had the key lost and a key standard replacement (non-fiat official and not remote).

Is it possible that the ecu has forgotten the key code and needs reprogramming? Or does this sound like a fried ECU?

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Welcome,,, do you have ANY of the original keys, remote or non remote(original) key? I'm fairly sure the BCM/immobilizer remembers the original key code, I stand to be corrected.

If it was working before then I can’t see why a simple job of changing a battery would make any difference. [emoji848]

John, unfortunately not, I was only issued with one key and im afraid it was long lost!

Typecastboy, that’s my thought exactly, hence why I’m seeing f anyone else has has the same issue??

Let's take one step back.
Why did you change the battery?

The main cables from the battery to the engine are prone to corroding inside, especially the black earth cable. From the battery it goes down to the gearbox and then across to the car body. The connections need checking for cleanliness and tightness, and the cable needs checking for resistance or continuity. Similarly the main red one needs checking too. If less than full battery voltage is getting through, cranking the engine will use too much power leaving insufficient to power the ignition. Such a low voltage will throw lots of random errors as the ECU gets upset.

I wonder if moving the cables out of the way to get the old battery out and the new one in have dislodged a cable somewhere.

As Portland Bill says, have a look at the earth connections first. The main two go to the near side chassis leg. I would undo them, take off the strap and give them a good wire brushing/sandpaper. It’s got to be something simple like that.

This happened to me this summer-not changed battery though. I also have a spare key by a non-fiat dealer which has always started the car. i used the spare, and the same thing happened-immobilser not recognised. When i used the original key it started fine-and then the spare worked too. I put it down to the very hot weather (which can fry a bettery) and it was idle for several days- Spare is fine now-so maybe low voltage. I would check the earths are all clean and all clamps are tight,

If the battery was properly dead dead.. then the car could have lost the last cycled key code in its memory (or it didn't get updated properly) so it's out of synch' with the key's code. My sister's Megane does this at least once a year since she frequently doesn't use it for weeks at a time.

She needs to get someone (Renort in her case) to re-cynchronise the key with the car. It costs her a fair bit since she has to have the car towed to the Renort service centre 500 yards down the road (they won't wander down ).. and aboot £80 for the actual "work".

If you can find a local mobile key mechanic then that might be easier than towing the car somewhere.


Ralf S.

typecastboy said:

If it was working before then I can’t see why a simple job of changing a battery would make any difference. [emoji848]

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IIRC Fiat use a rolling code immobiliser, and the code calculation will be stored somewhere in the car's memory. It's possible this information was lost when the battery was disconnected. If so, then it's going to need the services of a competent auto locksmith to get everything back in sync again.

I doubt Fiat will want anything to do with an aftermarket key; the only solution they are likely to offer is a new set of keys, reprogrammed to the car - which won't be cheap.

swifty500 said:

This happened to me this summer-not changed battery though. I also have a spare key by a non-fiat dealer which has always started the car. i used the spare, and the same thing happened-immobilser not recognised. When i used the original key it started fine-and then the spare worked too.

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This suggests the system can automatically recover itself if the code calculation is lost, but only if a genuine Fiat key is used.

Testing

I recently sold an ignition pack including both ECUs, ignition barrel, door lock and petrol cap. The buyer asked me if I had the plastic ring that sits at the end of the ignition barrel. I questioned this but luckily I still had it. This little bit of plastic with two wires on according to him, reads the chip in the key.

typecastboy said:

I recently sold an ignition pack including both ECUs, ignition barrel, door lock and petrol cap. The buyer asked me if I had the plastic ring that sits at the end of the ignition barrel. I questioned this but luckily I still had it. This little bit of plastic with two wires on according to him, reads the chip in the key.

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That would make sense NFC

Update, took it to a fiat dealership, they are claiming that the CAN (Central Area Network) is failing? and that they are going to use a donor ECU to see if it temporarily fixes the problem and if it does that a new unit will cost £503...? I know nothing when it comes to ECU computers but does this sound right? Fiat said they had the car on diagnostics for over 3 hours trying to figure the problem out? and they still don't know what's wrong. All I did was changed the battery... how can this all go wrong...?

PrincessMegan said:

Update, took it to a fiat dealership, they are claiming that the CAN (Central Area Network) is failing? and that they are going to use a donor ECU to see if it temporarily fixes the problem and if it does that a new unit will cost £503...? I know nothing when it comes to ECU computers but does this sound right? Fiat said they had the car on diagnostics for over 3 hours trying to figure the problem out? and they still don't know what's wrong. All I did was changed the battery... how can this all go wrong...?

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Which ECU are they talking about the one under the bonnet next to the airbox or the one behind the passenger glovebox/tray?

typecastboy said:

Which ECU are they talking about the one under the bonnet next to the airbox or the one behind the passenger glovebox/tray?

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Under the bonnet

PrincessMegan said:

Under the bonnet

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I had a problem with one of those. I bought one on eBay for £60. I took it with my car to a trusted local workshop who sent it off to be virginised. They have to zero it so the car thinks it’s new, the car then learns and sort of programs it to the car once fitted. The virginising cost £150.