Cranking but won't start

**Gazza243** · 13-07-2022,08:19 PM

Another note is that I'm guessing the previous owner had issues with diagnostics as the power wire for the diagnostics port has been separated from the loom and connected into the front of the fuse box

**VAG-Abound** · 13-07-2022,08:44 PM

Not sure what you mean there. There should be a black+blue (pin 1) and red+white (pin 16) each going fuse 1 and 13 respectively in the cabin block. One of those?

**VAG-Abound** · 13-07-2022,08:53 PM

If you have a multi-meter with a pointy probe check that all of the cabin fuses have 12V on the load side when the ignition is on via the little test point on top. And if not that they have it on the supply side. That's a pretty quick test compared with getting to the gateway, etc.

In the cabin fuse block there'll be a set of "rails" that each feed a group of fuses from an upstream fuse / relay. But only some of the "load" side slots will have a terminal. Shine a light in and check that any slots without a fuse don't have an empty terminal waiting for one. If you've been pulling and checking them it's very frustrating to eventually realise you put it back into the wrong slot.

**Gazza243** · 13-07-2022,08:53 PM

When I was checking the fuses inside it seems they have run a fused live for the aftermarket stereo into the fuse box, also connected to that is a red wire coming out of the loom that goes down to which I assumed was the diagnostic port but guessing that's not the case now you have told me the correct colours. I'll try and get a picture tomorrow and put it on here

**Gazza243** · 13-07-2022,08:58 PM

Unfortunately my multimeter gave up and I've yet to replace it but when I borrowed the vcds lead my mechanic mate (not wanted to bother him as he is extremely busy at the moment and i prefer to try and fix myself and learn) did check all the fuses like you said

**VAG-Abound** · 14-07-2022,08:06 AM

I'm not basing this on other threads, etc so you may want to search for similar to test the theory...

I'm wondering if the failure to start is due to the ECU and immobiliser (in the dash controller) not being able to communicate. I'm not sure if they use CAN bus for that, or something else. If they do then checking they can be seen individually when they are the only items plugged into the gateway and then as a pair might get things starting.

**Gazza243** · 14-07-2022,08:26 AM

Definitely something to try, is there any way to find out what modules I have in the car or shall I just pull the fuses?

**VAG-Abound** · 14-07-2022,08:42 AM

Found this while doing a quick search to see if I was misleading you: Powertrain data bus failure (CAN-bus) engine starts & cuts out! | UK Volkswagen Forum. Based on the comments in there referencing other cars / threads it looks like your problem is not unique - which is hopefully good if you can find the right place to read what the fix is!

Because I have a set of terminal pin demount "wigglers" I would plan to remove each pair of CAN wires one-by-one from the gateway plug. Are you suggesting de-powering each module in turn to see if it has any effect? I can see how that could work if it is a logic type of problem, but AIUI some buses have multiple items connected directly or via other modules - so it would be hard to figure out what to do in which order. Also may not work if there is a damaged wire on the way to the module.

It's easy to over think / plan this sort of investigation. Based on what you've said about the under-dash rewire, etc first thing is probably a good look around. It may turn out to be something obvious when you see it.

There haven't been any rain leaks or drink spill on the dash events have there?

**Gazza243** · 14-07-2022,08:50 AM

That's my first step to have a look under the dash and around to see If there are any obvious broken wires (which I had on drivers door) I'll have a look at the other thread aswell to see if there's anything on there that may point me in the right direction. Even if I can get the canbus working and still doesn't start at least I'll have some sort of diagnostics to go by. I'm at the car now (it broke down by my kids school and haven't moved it) so I'm going to start the investigations now
I do appreciate all your help thank you