Seat Exeo non-start after ECU flood - ECM not responding

[111gsi]

Afternoon all,

My Exeo decided to celebrate the rainy season by giving its ECU box a nice bath (despite the scuttle bungs being removed as soon as I bought it 3 years ago?!). Noticed the engine fans coming on when the engine hadn't been running. Started the engine, fans stopped for about 5 minutes. Then came on again. Did this a couple of times and then the fans stopped coming on. When I came back to investigate, engine turned over but battery was too flat so it didn't start. Wouldn't take a jump (not turning over at all) and after charging the battery overnight, won't turn over. Meanwhile I discovered the water in the ECU box, just up level with the bottom of the relays.

Long story short, have dried it out, removed relays and dried and cleaned them up, but still no turning over.

VCDS can't communicate to the main ECU but can do all the other systems. Central locking, electric windows, radio, HVAC etc. all appear to work normally. When I turn the key, the Engine Management light doesn't illuminate along with all the others - from reading VAG forums this looks like bad news for the ECM. I've checked all the fuses in the ECM box, and the ECM fuse in the dashboard (Fuse 43) is good and is getting 12V when the ignition's on.

I presume I'll need to replace the 457 and 645 relays because they were corroded inside, but would these prevent any power going to the ECU?

If there are any VAG gurus out there who know a handy way of checking the ECU without sending it for testing, I'd be delighted to hear from you! And assuming it has been fried, who would be the best locally to get the car back on the road?

Thanks in advance...

 

[finn28]

Be interested to see how this goes for you, I've an A4 in my yard that got water damaged and it's been lying up for ages. Initially I was facing the same issue with no reading from the ECU. After replacing a few relays, BCM, CCM, etc, I eventually got it communicating with the ECU again.

 

[n3il]

The 457 relay is for the glow plugs, it won't affect it starting it will just cause the engine light to go on . The other one is possibly fuel pump. Is it not even turning over?

 

[111gsi]

The 457 relay is for the glow plugs, it won't affect it starting it will just cause the engine light to go on . The other one is possibly fuel pump. Is it not even turning over?

No, not trying to turn over at all. All lights come on as normal when ignition turned on, apart from the MIL light. Also throws a TPMS warning, which I can reset but comes back immediately. This looks to be some problem with comms with the ABS module.

I paid for an hour of ERWIN and downloaded the full genuine SEAT workshop manual and wiring diagram so will get a nosey through that. I normally work between the Audi A4 B7 and B8 Haynes manuals because the Exeo is basically a B7 with a B8 engine.

Also managed to persuade the family to help me push it in the garage so at least I can poke about in the dry!

 

[Nicky Glanza]

@Tam9n

 

[n3il]

Take the 645 relay out and bridge it to rule it out

 

[111gsi]

Happy to say I got a resolution and the car is running normally again.

Replaced the 645 relay and 457 glow plug control unit with new genuine parts (not cheap but I didn't want to risk Chinesium with 60 Amps running through...).

Car started as normal, and VCDS can communicate with all systems and cleared the stored faults from before.

Two things that helped me along the way:
Seat erWin
I paid €8 for an hour's access and downloaded every manual, circuit diagram and technical training resource for every SEAT I could think of. Very helpful indeed. In the case of the Exeo, there are several permutations of layout for the ECU plenum chamber and the 645 relay does different things for different models. The diesels changed in 2011 and 2012, so mine turned out to be the last version. Saved tons of time rather than googling random info about Audis.

How to diagnose a faulty ECU - No Comms
This YouTube channel is very good for directing fault finding for a novice. You need to know the pin-outs for the ECU (which I got from erWin) but it seems a good resource.