Accessing BCM

[Tander]

I posted this thread last week: https://www.seatcupra.net/forums/threads/windscreen-wiper-issue.481775/

I'm starting to think my issue is not the wipers themselves. They still don't work and neither does the front washer. The rear wiper and washer works (So since its the same pump, the pump is fine) - but I now have other issues on the car:

- Alarm will go off after ± 30s of locking the car
- Outside air temp is wrong (Reading -17c to 36c )
- Additional fault code about Data buss missing coms (brakes and BCM I think)

This to me points to something else - like the BCM. I read a post on here were someone mentioned their car had odd electrical issues and the culprit was the BCM getting corroded (Suspected leak from washer pipe)

I'm starting to think this might be my issue too - since the issues have gotten worse and they happened when the weather was wet - the alarm was always when it had been raining the last few days - might be conisidential )

Anyway, I want to access the BCM. where is this located and how difficult is it to get to it?

If I need to replace it, can I just order one off eBay and use my OBDeleven dongle to program it?

Thanks!

 

[tracktoy]

Happy to be wrong but i am afraid that the BCM has component protection, if that is true then you cant use OBD11 to remove it I am afraid.

Hopefully others can confirm.

 

[grabania]

BCM have component protection and it stores which keys are attached to the car. It is not just p&p, it requires specialized tools, e.g. ODIS with online access at least.

 

[Tander]

BCM have component protection and it stores which keys are attached to the car. It is not just p&p, it requires specialized tools, e.g. ODIS with online access at least.

Alright, makes sense. Thanks

It might just be corroded connections / wires to the BCM causing these issues or would a faulty BCM show more serious issues?

Just trying to figure out the next steps before I take the car somewhere to get looked at.

I have checked:

- All fuses and relays
- Wiring from wiper motor to fuse base in engine bay
- Pump is operational
- Rear wiper works

To me it's an electrical issue somewhere that affects more than one system and I can only think of the BCM.

 

[Tander]

Happy to be wrong but i am afraid that the BCM has component protection, if that is true then you cant use OBD11 to remove it I am afraid.

Hopefully others can confirm.

Seems it, sadly. I suppose thats a dealership-only type of job?

 

[tracktoy]

Yes or I would have thought that a reputable Retrofit company may be able to help.

One of our sponsors https://www.eastyorkshireretrofits.co.uk can confirm

 

[cairus]

Jeder, der online bei Geko ist, kann CP freischalten.

The Other way, you Copy the BCM

 

[Tander]

Yes or I would have thought that a reputable Retrofit company may be able to help.

One of our sponsors https://www.eastyorkshireretrofits.co.uk can confirm

Yeah, looks like they do it:

Control module replacement / Component Protection adaption

When replacing modules on your vehicle, you'll often find there's a built in security feature called Component Protection.

eastyorkshireretrofits.co.uk

I need to first try access the BCM to see if it has any signs of water damage / corrosion to confirm if it might need replacing

 

[James_R]

The BCM is located at the mid part of the N/S/F A-pillar. You have to remove the glove box to access it.

On the mk3 Leon the front wipers and alarm siren share a wiring loom that runs in the bulkhead, it's susceptible to water ingress and damaged wiring. Have you had that loom out to check?

Replacement is better off carried out with the correct equipment and needs to be the correct part number.

 

[Tander]

The BCM is located at the mid part of the N/S/F A-pillar. You have to remove the glove box to access it.

On the mk3 Leon the front wipers and alarm siren share a wiring loom that runs in the bulkhead, it's susceptible to water ingress and damaged wiring. Have you had that loom out to check?

Replacement is better off carried out with the correct equipment and needs to be the correct part number.

Hi James,
Thanks for the reply.

So I pulled the wiring loom from the wiper motor to the engine bay. It comes out of the crawl into the engine bay, near the battery. I didn't inspect the wiring loom inside the engine bay as I figured it's very unlikely to be damaged from that point onwards and would not be getting wet when it rains inside the bay (I could be wrong)

I did notice that part of the loom, passenger side was soaking wet - but it looked fine - there were two joins, that also:

A) Looked fine
B) Looked like might have been factory?

I did not look at the smaller bits of wiring loom that went from the crawl bit, under the windshield to bulkhead.

I've attached some images:

You'll see in one of the photos, where the tray is wet - but I couldn't see anything obvious there.


Some of the codes I get on the car are:

- Brakes fault - Databus missing message: U112100
- Body Computer 1/veh. elec sys CM/cent elec - U102100
- Wiper motor control module - No Comms - U10A300
- Siren / Alarm horn for anti-theft warning sys - No Comms - U10F300

No fault code for front washer - although it doesnt work.
No fault codes for outside air temp sensor being wrong (I guess it might not "know" its "wrong" ?)

These codes come back after clearing them with OBDeleven - sometimes the alarm is not there but does come back

This was why I started thinking it's BCM. But if you're saying the siren and wiper motor are shared.in the same area it might be that?

Should I take a look at the BCM connections to see if they're wet - or is that very unlikely? Maybe I should look at the loom again in the crawl / tray by wiper motor?
Just need to try resolve this asap and without spending thousands at a garage.

 

[James_R]

I'd open the loom in the bulkhead up as much as possible. It's usually the LIN signal wires that end up with water in and causing a drop on communication.

 

[Tander]

I'd open the loom in the bulkhead up as much as possible. It's usually the LIN signal wires that end up with water in and causing a drop on communication.

I removed all of the loom tape from wiper motor, till the loom exited the bulkhead into the engine bay. The LIN wire is the green/white wire from wiper motor plug?

As I mentioned, I couldn't see any issues. Would I have better luck testing with a multimeter? I dont have one, but can grab from Halfords.

What should I be looking for? I was expecting to see a wire that was bare / broken - maybe I need to look for other "signs" of damage?
Appreciate if this is all obvious to most; but first time I am trying to fix an electrical issue on a car.

Maybe I could run a new LIN wire from engine fuse box to the motor plug as a test as well to rule out the LIN being at fault? (Probably a dumb idea, just spit-balling )
Thanks for the help. James.

 

[James_R]

The wire doesn't tend to be broken, it's usually that the insulation has opened up and allowed water inside the wire. It corrodes the copper and creates a high resistance situation.

At the siren you should have a battery live, earth and around 10-12v on the LIN wire, ideally you need to scope the LIN signal to gain an accurate depiction of what's occurring.

The same for the LIN at the wiper motor.

 

[East Yorkshire Retrofits]

We’d be happy to take a look at this for you. We can diagnose and perform any necessary repairs

 

[Tander]

We’d be happy to take a look at this for you. We can diagnose and perform any necessary repairs

Appreciate the offer; but I am no where Near East Yorkshire. Unless you're able to callouts to the South East?

Car is booked for the local garage to look at it on Saturday if I can't fix it by then - but I am not confident they'll be able to fix this.

 

[Tander]

The wire doesn't tend to be broken, it's usually that the insulation has opened up and allowed water inside the wire. It corrodes the copper and creates a high resistance situation.

At the siren you should have a battery live, earth and around 10-12v on the LIN wire, ideally you need to scope the LIN signal to gain an accurate depiction of what's occurring.

The same for the LIN at the wiper motor.

Just looked up on scoping. The tools for that will cost a bit; so perhaps its best to get someone with the correct tools out to have look for me and pay them - as it seems a visual inspection of the cables is not really enough. (As I couldn't see any damaged cables myself - and only those joins in the photos attached)

 

[East Yorkshire Retrofits]

Appreciate the offer; but I am no where Near East Yorkshire. Unless you're able to callouts to the South East?

Car is booked for the local garage to look at it on Saturday if I can't fix it by then - but I am not confident they'll be able to fix this.

We're not mobile unfortunately, sorry

 

[James_R]

Just looked up on scoping. The tools for that will cost a bit; so perhaps its best to get someone with the correct tools out to have look for me and pay them - as it seems a visual inspection of the cables is not really enough. (As I couldn't see any damaged cables myself - and only those joins in the photos attached)

You can pick up a single channel scope for less than £30

 

[Tander]

You can pick up a single channel scope for less than £30

Oh I was seeing some for £100+

Amazon have this: https://www.amazon.co.uk/Oscilloscope-Handheld-Real-time-Beginners-Instrument/dp/B0CRHMLGVX

But that won't get to me until Saturday. I'll see if any local shops have something like this instead - if I can get it tomorrow and just check before taking the car in.

Ideally I need this issue resolved by Saturday.

Thanks James

 

[Craig.]

Wiper module (J400) and alarm siren (H12) are on neighbouring pins on the same BCM plug (Pins T46b 30 and 31 respectively) which is the smaller middle plug, for when you gain access to the BCM.

Side note, it helps if you have the hands of a 10 year old girl to get decent finger access to the plugs LOL

As above, the BCM holds Component Protection (CP), key data for remote central locking and controls a whole host of things on the car which some likely won't work properly without the correct parameters loaded. Genuine ODIS with authorised online access is your best friend for this.

I am not familiar with OBD11 (and it's ilk) but if it has similar functions and features as VCDS then I'd check the output from the wiper stalk and try and trigger the wipers from the diagnostic tool just to confirm everything outside of the wiper motor is correct as it's a 10 second job and adds verification that the problem is the motor end.

I'd also test for power at pin1 (Red/White wire) on the plug at the wiper motor end of the loom. Even though the "No Comms" fault codes are pretty solid lines of investigation to follow, always best to cover all avenues before parts swapping.