Wiring loom dashboard failure

[Stoohall]

Hi guys - I need your help. I’m converting a 2015 l4h3 into a campervan. Removed all seats and floor etc, but the wiring loom on the offside of the vehicle was constantly in the way.

I had to lengthen the entire loom by 10cm, so did that about half way down and passed the loom behind the framework of the van to get it out of the way.

However - I’ve now lost the entire instrument panel. All clocks are dead.

The van starts fine, parking sensors and lights all work as expected.

I’ve just read up on how the aux battery works - and testing shows that this battery doesn’t hold charge - but surely that’s nothing to do with the instrument panel? It’s causing havoc with the step though.

Does anyone have any ideas on what could cause this?

And you don’t need to tell me, lesson learned, I’ll never mess with a wiring loom ever again.

[jack2006]

Also got an L4H3 2016 minibus that we are converting at the moment.

The harness on the drivers side on mine goes to the powered step module (lower rear on minibus drivers side) passenger roof lights, rear external light clusters and I think thats about it. The medium speed CAN bus goes to the step moduleso it probably would not be over keen if you cut through all of the loom in one go although the CAN bus driver IC's usually have some tolerance to short circuit to meet automotive standards.

I had a raft of problems at one point and it was due to the batteries (both in my case) being discharged quite low. This gave both loads of DTC's when read with 'ForScan' in most of the can modules and lots of message centre display messages,, such as failed injectors, low oil etc.

It might be worth disconnecting both batteries, then charging both the batteries back up fully before reconnecting to see if that resets things.

[Stoohall]

I’m still having this issue. I’ve replaced the batteries and everything is charged - but I just can’t get it to wake up. When I replace the fuse for the instrument cluster the needles move slightly and I can hear the system going through a process - but not start up. Has anyone seen this?

[Frag]

Sounds like you have a fault on the CAN communication lines….
If this problem has started since you lengthened the wiring loom I would be starting there.

You will need a code reader and/or a multimeter to check the CAN network for short or open circuits.
If the van is still currently stripped,try unplugging the power step module which is at osr corner behind the trim panel.
A fault in any module on the network,or in the wiring can shut down everything on the same CAN lines.

Also,be aware,there are some connections/male and female multiplugs along the length of some looms that don’t look to be connected or ‘for anything’ that have CAN wiring running through them,and if disconnected or shorted,will kill the entire network.
(There is such a plug above cab headlining / parcel tray in a mk8 for example.)

[Stoohall]

Thanks so much for this. I really appreciate your input.
There is a plug on the loom, now disconnected, that went to a light in the headlining which has now been removed. Is that possibly a problem?! I no longer have the light - it was thrown away with the headlining. Is there an easy way to terminate the plug correctly?

[Frag]

That would depend…
If it was purely for an interior lamp,2 pin connector and only 2 wires,it won’t cause the problem.
If you’ve unplugged a larger block connector to another loom,then you could have problems.
Is this in the cab area,or rear of van ?
(Which I assume with power step used to be a 17 seat bus.)

Have you got access to the power step module ? Tried it with that unplugged ?

[Stoohall]

The connector I'm talking about is further back. Probably about the middle of the van, and was four wires. One permanent live, one live with ignition. I don't know what the other two are.

I have access to the step module. I unplugged it and the instrument cluster didn't wake up. I removed the battery for 20 mins or so and reconnected - it then did the needle-jiggle thing again - which makes me think it has at least done some sort of restart. But nothing further happens. The side step, for the mostpart, behaves correctly - although sometimes doesn't want to come out unless the ignition has been on recently.

I'm totally at a loss with this - pulling my hair out.

[Frag]

Have you retraced your steps since extending the loom ?
Checked all of those connections are correct ?

Sidestep and dead cluster can be linked,due to being on same CAN network.
Also you can ‘stow’ and ‘deploy’ the sidestep through cluster menu,turn it off totally.
If the step is deployed,engine will cut if you drop the handbrake or attempt to drive.

[Stoohall]

I guess my next step needs to be checking that each of those 80-something wires are connected cleanly. Is there any way to identify the colours of which are can bus specific? Because everything that runs through that loom that I can check (indicators, parking sensors etc) all work perfectly.

[Frag]

Generally speaking CAN wires in a loom will be twisted spiral around each other.
You’d need wiring diagrams really to check properly.

This will explain what you are now up against,and either help you…
Or,melt your head…
https://youtu.be/gsWG6hFxMl0

[Stoohall]

Yes, I did actually skim through that video earlier today. Because this is an ex-minibus and is now just about complete as a camper, I have pretty easy access to all the modules. The only part that's covered is behind the driver seat - it's now a shower cubicle and if I have to remove that, I'll basically throw in the towel on this project.

I watched the video start to finish. I do understand it all - I just have limited tools.

I guess my next question is - if I unplug a module which is causing a short on the can bus - would the dashboard immediately wake up? Or would it need some sort of restart like a battery connect etc?

The video shows the guy with an unplugged module, and returns to an illuminated dash - but doesn't really show how it happened.

Tomorrow I'm going to try to source an OBD breakout like in the video that could show me clearly if the bus is live.

[Frag]

Usually the cluster will come back once you disconnect the fault,just doing a key cycle on and off after any changes would be wise though.
I think it’s more likely to be wiring itself than a module fault,but they’re easier to isolate.

Shouldn’t need anything to be reset or cleared.

My next step would be to disconnect the rear loom at osf dash area and see if cluster comes back,then you can at least confirm the cluster itself if still ok,and the problem is in that front to rear O/S loom..

Problem being,disconnecting that rear loom usually means removing the BCM,and it’s mounting bracket to get at the connector,(located at the strut top area)then roughly plugging the bcm back in with it disconnected to check.

If you had access to diagnostics,dtcs or seeing which modules are/aren’t responding on network test may point you in a certain direction.
You can have a fault on canbus wiring that’s in the factory generic loom,for a module your spec of van doesn’t even have.

[Frag]

And also,
This could be absolutely coincidental,cluster failure….

[Stoohall]

Yeah that would be another fun outcome. Any way to eliminate that possibility without sourcing another instrument cluster?