Hi,

I'd like to ask for any advice on an issue that's just cropped up, but firstly just a quick note on this my first post to say thanks for the amazing info on this forum, which was so useful while I was buying my GTC. First thing I did was to buy the VCDS system so I could scan codes, and was happy to see nothing major on my first scan. It's an early GTC from 2007 so I was also happy to know about and be able to confirm I wasn't buying one with the older routing of the vacuum pipes. Which is just as well because...

3000 miles after buying the car and driving her to the south of France and back she still runs like a dream but the following sequence occured over the last two weeks:

1. A sudden and very loud continuous whistling sound on the motorway, went away after a few minutes
2. A very quiet intermittent "morse code" beeping/whistling from the engine, went away after a few days
3. No issues for a week or so, then I hard-wired a dashcam, and topped up the oil and filled it with petrol
4. Engine light came on shorly after
5. The only relevant fault is Engine 1 saying "please check DTC Memory of ECU Number 2"
6. If I clear the fault codes the engine light goes off for one second then returns, as does that fault code on ECU1. This happens regardless of whether the engine is running.
7. Noticed for the first time that my VCDS is unable to connect to Engine II, and wasn't able to in any of the previous scans I'd logged since I bought the car 2 months ago.
8. Noticed for the first time that the vacuum tubes at the rear of the engine have various minor splits, and tape wrapped round them. One of the bits of tape has clearly split.

So my guess is that one of the bits of tape broke, resulting in the whistling from a split in the vacuum tubing which settled down as the hole in the tape got bigger. That eventually caused ECU 2 to report a fault bad enough to trigger the engine light (possibly the extra oil tipped it over the edge) but I can't see what it is because I can't talk to ECU 2 from the scanner. And of course this means I can't clear the fault code in ECU2, so the light stays on even if the root vacuum problem has been mitigated by a bit more tape.

I'm booked in to have someone look at the vacuum pipes.

What I'm puzzled by is what mechanism could exist whereby the ECU 2 is obviously functioning and talking to ECU 1, but the VCDS scanner can't connect to it. Logically this sounds like a failure in the connectivity between the ECU 2 and whatever the bus is that VCDS connects to, while the comms between ECU1 and ECU2 is unaffected. I'd like to get to the bottom of this before being told I need a new ECU when it goes to the garage.

Other info: I've peeked at the ECUs and there is no water or anything obviously bad, but I haven't fully taken them out to check for corrosion etc. The engine runs smoothly including at idle. The loud whistle can be replicated at any time by not pushing the dipstick in properly, but I don't think that was it. The oil and fuel caps are on firmly. I've added to the tape round the vacuum pipes but it won't make the engine light go away. It suddenly occurs to me to unplug the dashcam but I used a spare fuse position so it's hard to believe that's related.

Would it be worth pulling the ECUs and cleaning the contacts, that kind of thing? Or disconnecting the battery for a bit? Or am I completely wrong about how ECU 1 & 2 talk to eachother and the VCDS scanner? Any ideas for troubleshooting and avoiding a new ECU "just in case that helps" would be gratefully received!

Many thanks,

Danny.

 

Hello @DannyGTCRichmond ,
Are you using a laptop with your Ross-Tech VCDS, or the cellphone application with the VCDS, as I have had conversations with Ross-Tech as to engine-ll not communicating after scanning engine-1 while using my cellphone to scan, with the cellphone I use "engine-other" to clear ecu 2, it won't show the faults of ecu-2, but it will clear all ecu faults, with my laptop I have no issues scanning ecu's 1 and 2.

Johnny

 

Hi @Johnny Hotspur GT thanks for that, that's interesting that you've also seen the two ECUs responding differently. I'm using the laptop. It's fascinating because the circuit diagram shows that the two ECUs are simply connected to the same "k-wire" which goes straight to the diagnostic socket. So I thought there could be no excuse for ECU2 not communicating other than a problem with the wiring or a genuinely faulty ECU. But if you've seen something similar, albeit with a different interface, that's very interesting.

I removed the ECU2 connector and cleaned it - it looked fine but worth a try. It didn't restore the diagnostic comms but did remove the CEL light. And it hasn't returned after 200 miles of driving. If there was a leak it wasn't nearly as bad as I'd thought, just some minor cracking at the usual place at the rear of the engine which was easily sealed. There are no symptoms, and I now have a sneaking feeling I might even have induced the CEL by messing about with the dipstick while it was running!

I'd tried Engine Other - but only to pull the faults not to clear them. I'll try that next time, thanks.

One more question - is it safe to simply swap the two ECUs over? I know they are the same hardware / software etc but I wonder a) if they have to relearn parameters and b) if there is any danger of the car becoming imobilised. I'd like to try that swap to see if it's the wiring or the ECU itself that is reluctant to talk to the diagnostics port.

Thanks again, cheers.
Danny.