Immobiliser faulty or ECU?

[Zax]

Hi Folks,

So I've had 2 years of mostly problem free motoring from my little black Puma, right up until Saturday just gone.

Driving to a friends house in vicious rain and wind on Friday evening I thought that the speedo was acting strange. It didn't seem to be responding properly to changes in speed. I worried a little as I'd recently needed to have the speedo drive unit and cable changed when the speedo just packed up over summer, I thought something further might have been broken/an issue. Leaving my friends house later that night I kept an eye on the speedo and it all seemed fine so I figured that it was probably just my imagination.

The car remained parked all day Saturday whilst Plymouth was hammered with high winds and torrential rain. Needing to visit a different friend in the evening I jumped in the car, turned the key, nothing. Well nothing other than the immobiliser light flashing really fast, though I didn't notice this at first. I figured that the transponder in the key had done something weird so went to get the other key. Tried that one, still no joy. So researching led me to reading the fault code from the light. Fault 12 is supposed to be a faulty transceiver coil. So off to eBay Sunday morning, found another one, fitted it. Same problem. I wondered if the ECU might need resetting so left the battery disconnected for an hour. Still no change.

I'm hoping that there might be some bright ideas from the clever people hereabouts before I ring the garage for the likely-to-be-expensive "please come and pick up my totally immobilised car" phone call.

So just to recap. All lights etc come on. Electrics work. Remote locking works. Both keys usually start the car fine. Car was fine the day before, showing no signs of trouble other than the speedo which could have been my imagination or just driving into a gusty headwind.

I'm wondering if the ECU has somehow got wet? I have this feeling that the immobiliser fault code is useless. Seems odd that such a simple piece of tech would just fail from one day to the next with no prior indication of trouble. Also seems unlikely (but not impossible I guess) that the replacement part would also turn out to be faulty.

Any thoughts anyone. Love my Puma, want it to go vroom again.

 

[red]

Are the foot wells damp? The ECU is inside the car up behind the dashboard.

 

[Ian G]

Just to allay your fears about it being expensive, if the ECU really has got wet and failed then you're only really looking between £30 and £50 depending which one it is to replace it.

As above you need to get to it and check it over first. Without any disassembly at all you can inspect the grommet above it that comes through the bulkhead in to the engine bay. Passenger side behind the fuse box. And with the interior carpet back, passenger side behind the fuel cut off badge you'll need a pozi screwdriver, an 8 and a 10mm socket and a drill to get rivets out you can have it out the car for a closer look.

Dare say it may even be worth whipping the lid off to see if that gives you any clue. I wouldn't poke around unnecessarily but if its scorched or discoloured then that may well be some form of diagnosis on the cheap before you book it in anywhere.

 

[Zax]

Thank you both for the replies, I'll check the footwell for wetness and have a look at the grommet to see if there's any indication of water ingress. Then get into it further and have a look at the ECU.

A friend has offered me the use of an ODB II thingy. Would either of you have had any experience using one of these? What sort of codes should I be looking for if the ECU is damaged?

If it does need to be swapped out I'm guessing I'd need to have the transponders in the keys recoded to the new ECU, is that correct? Probably not something I can do myself?

 

[Ian G]

You can do it yourself, ensure you get the transponder with the ECU and fit that to your key.

 

[red]

Zax, usually you wouldnt expect any codes so run through and see what it picks up, I guess if the ECU is damaged it may not work at all since this is what you're trying to read the codes from.

I've used both a cabled one to a laptop and a bluetooth one to my phone, not for a while but they are handy for clearing error lamps and checking sensors.

You might have the problem that cheap ODB readers are notoriously unreliable especially at so if it can't connect to the ECU you may not know whether it's the ECU or the reader.

 

[Zax]

Well There doesn't seem to be any wetness in the footwell and the grommit behind the fusebox looks to be in good condition. One thing I noticed was that the top of the engine fusebox was not fitted corrrectly, or even at all. It was serviced just a couple of weeks ago by my local garage and I'm wondering if it maybe got knocked whilst the pollen filter was being changed as I think that's behind it? I would have thought that water getting into the fusebox would create more and different problems than just a non functional immobiliser though.

Colour me stumped so far.

 

[red]

hmm then I guess it must be something in the engine bay, wet fuses wouldn't be too happy I doubt, have you checked to see if any have blown?

 

[Zax]

Not yet, I was on a tight schedule but I will look later. I guess it may have nothing to do with either the crazy rain or the loose fusebox cover but it being fine before the 6 hour deluge of sideways rain and then broken afterwards seems to correlate. Though I guess correlation doesn't always equal causation!

I'll check all the fuses this evening and then hopefully get my hands on the ODB doohickey which might provide another avenue of investigation.

 

[Frank]

[post]345368[/post] I guess it may have nothing to do with either the crazy rain or the loose fusebox cover but it being fine before the 6 hour deluge of sideways rain and then broken afterwards seems to correlate. Though I guess correlation doesn't always equal causation!

Put the two conditions together and it's a pretty safe bet though. Wind can make rain do some very odd things.

Five of the fuses in that fuse box, including the Engine Management one, require 'specialised knowledge' to replace. So maybe find out what that is first or get a mobile auto electrician in, I reckon.

 

[Zax]

Ok so Friday evening I removed each of the fuses one by one and sanded the contacts clean again as they looked pretty ganky. Still nothing changed. Car wouldn't start immobiliser light flashing fast. Saturday a friend brought me an ODB II reader. After realising that you need to turn the ignition to the on switch to get it to work (durrr!) it reported no error codes. I was all but resigned to phoning the garage for a pickup when I noticed that the immobiliser light was no longer flashing. Turned the key further and sure enough the Puma started!

So I'm not sure if it was a case of the new transceiver, cleaning the fuse contacts, the fusebox drying out or the ECU scanner working some arcane magic (despite recording no faults) but the car is driving as great as before. Thank you all for your help and suggestions. I know one thing for sure, I'm definitely going to keep an eye on that fusebox and ensure that it is sealed at all times!

Oh and Frank, I wonder what the specialist knowledge is? There seems to be a selection of very tiny fuses and some serious whoppers. But they all just look like fuses. Most seemed a bit corroded so all I did was take them out one by one, sand the contacts and then push them in and out a couple of times. Even checked all the relays in there but they seemed all clean.