Electrical gremlin on a TSI (LIN cable fault?)

[jekyllandhyde]

Hi all,

I seem to have a bit of an electrical gremlin that I am trying to get to the bottom of...

The Van:
I have a 2019 150bhp TSI (engine CJKB) Trendline which has had a Kombi conversion carried out at some point by Leighton Vans.
Pendle Remap, So-Low (-50mm ish), Fuel Covert Alloys (BFG K02's), aftermarket rear windows, swivel seat base, roof bars, aftermarket stereo.
Recent Sachs performance clutch and uprated AEM R8 ignition coils (+10%).

The symptoms:
1st symptom, the van wouldn't attempt to start and from memory an the ESC fault on the dash. Battery voltage 12.3 volts.
Whipped the battery off and charged it up, happy days, all back to normal. Various fault codes for communication issues all cleared ok. (ABS, ESP, start/stop, Engine management, door locks, dash and a few more I cant remember)

Went for a new clutch and all still seemed well for a few days but then wouldn't start until the 2nd or 3rd attempt with the key until it finally turned it over and started it. I put this down to the battery being 5 years old so got a new battery. Again all fine for a few days untill the same thing happened....it was taking 2 or 3 attempts .

Until the other evening it wouldn't even attempt to start. There were multiple fault codes standing similar to the other week. These being rear from my ANCEL VD700:
2/2 03158 Information electronics control module 1
1/2 01314 Engine control module (ECM)
2/2 U112100 Databus missing message
1/2 U111100 Function limitation due to missing message
1/10 U112300 Databus error value received
10/10 U112100 Databus missing message
2/2 03442 Return message rear lid closing condition (door was open)
1/2 03303 Return message for left rear door closing condition (door was open)

It wouldn't jump from leads, or bump start from pushing the van.
However, I did get it started by removing the battery and visually checking the electrics beneath the battery for water ingress, and cleaning the cable connection onto the battery terminal that leads to the main fuse bus bar beneath. This might have reset the BCM because it started up very lumpy for the 1st few minutes.

Symptom 3. After I got the van home I started it to move it on my drive and it turned over but didn't want to fire. After releasing the key to give up, the starter motor carried on turning over for another 4 seconds or so and the engine finally started. I'm thinking this must have been a signal from the stop/start system if the key was released?


A few points that I will be checking and sorting are:
Re-sealing the roof bars due to water ingress into the rear near side wheel arch area.
Checking the cable connections that might have been disturbed when the clutch was replaced, and if possible checking their continuity.
Checking of the connectors beneath the floor of the swivel base twin front seat, because I think the ABS sensors link into the wiring loom under there.

Having sifted through this forum for the last week or so I thought I had hit the nail on the head when I have read the multiple posts regarding the LIN cable issue that runs between the BCM and the Alternator. However....looking at the pictures in this post Stop/Start error after pressing the button ! and comparing them to my van, I don't have anything that resembles this, I am guessing that is because mine is a petrol TSI.


Has anyone replaced the LIN cable on the TSI before or had anything similar?
Looking in the wiring diagrams the colour is still yellow/green as per below.

Any help much appreciated.

 

[roadtripper]

Symptom 3. After I got the van home I started it to move it on my drive and it turned over but didn't want to fire. After releasing the key to give up, the starter motor carried on turning over for another 4 seconds or so and the engine finally started. I'm thinking this must have been a signal from the stop/start system if the key was released?

For reference mine's diesel but this is totally normal start/stop behaviour - the ignition key on a start/stop vehicle is just a trigger, you can let go any time and it will complete that start cycle. I'm now in the habit of just flicking it to start briefly and letting it get on with it.

If you have start/stop then you should also have a shunt on your negative battery terminal, and between that, the alternator and the BCM a LIN bus wire. Regardless of fuel it's doing the same thing.

 

[jekyllandhyde]

For reference mine's diesel but this is totally normal start/stop behaviour - the ignition key on a start/stop vehicle is just a trigger, you can let go any time and it will complete that start cycle. I'm now in the habit of just flicking it to start briefly and letting it get on with it.

If you have start/stop then you should also have a shunt on your negative battery terminal, and between that, the alternator and the BCM a LIN bus wire. Regardless of fuel it's doing the same thing.

Thanks for the reply roadtripper, I didn't know that.
I'll have a look and see if it's possible to check their continuity.

Cheers.

 

[jekyllandhyde]

So thought I'd post a quick update.

I have removed the roof bars and re-sealed these. There isn't any water getting into the back near side wheel arch area now so happy days!

The continuity of the LIN cable from the negative terminal on the battery and the alternator tested good, even with flexing the cable. However the battery still isn't charging properly (I'll come back to that). I wanted to test to the connectors in the E-box shown as T10l in the above drawing but i cant find the connector....hence i went straight to the alternator.

The sliding door lock and handle wasn't working consistently and sometimes didn't work at all. When looking into this I noticed that by removing the plastic cap on the top of the stalk (the part that moves up and down when you lock/un-lock the door) allowed the lock to work correctly. Any slight resistance on this what so ever and it wont pop up to unlock the door. Tweaking the metal rod that leads up to this plastic cap sorted this issue. Apparently if the locks don't lock as they should it can keep part of the electrical system 'awake' and drain the battery.

The van starts and drives great now, however I am not convinced that it is charging the battery properly. Monitoring the voltage at the 12v socket next to the gear stick fluctuated between 12.3V and up to 14.9V, and isn't consistent. I just pulled into work and now its down to 11.9 - 12V ish.

I think I'll do a battery drain test with it turned off and locked to make sure its only 0.035 to 0.04a next.

 

[roadtripper]

Monitoring the voltage at the 12v socket next to the gear stick fluctuated between 12.3V and up to 14.9V, and isn't consistent.

That's exactly the behaviour I would expect with a smart alternator - generally the electrics will be running off the battery (12.3v) and then short bursts of fast charging (14.9v)

However 12.0v is "recharge now" level and is unexpected if you've recently had the engine running and there is no good reason for a battery drain.

How old is the battery? If it's original (2019) then it's likely end of life as start stop works the battery quite hard.

 

[jekyllandhyde]

That's exactly the behaviour I would expect with a smart alternator - generally the electrics will be running off the battery (12.3v) and then short bursts of fast charging (14.9v)

However 12.0v is "recharge now" level and is unexpected if you've recently had the engine running and there is no good reason for a battery drain.

How old is the battery? If it's original (2019) then it's likely end of life as start stop works the battery quite hard.

Ok I thought that might be the case.
The battery is only a few weeks old. I still need to register it though. But I would have thought if it still thinks the battery is the old one then it might be charging it more than it would if it thinks its a new one?

 

[roadtripper]

If you didn't do the coding to set the new battery parameters (for capacity) or change the serial number (to reset the health history) then yes it will not behave as normal for around 10 charge cycles as the BCM adapts to the new battery.