Brake lights always on with key position on and when running

[pandasunglasses]

Hello.
I have an Ibiza 6j 2008 1.4 tdi.
2 days ago I noticed all 3 brake lights came on with key positon on, even when the car is not running. Same thing when you start and run the car. Pressing the brake pedal doesn't change the brightness of the brake lights. They light up with/without the headlights turned on. There are no faults showing on the dash. I have not checked for faults with VCDS yet. Hazards, turning signals, reverse lights all work fine - checked them all.

I tried changing the brake light switch with a brand new one and nothing changed. The new switch is not from SEAT - it's a different brand, not sure if that makes any difference. With the switch completely disconnected the brake lights were still on.

One of my tail lights fills up with water and I thought maybe some bulb has gone bad but no, tried removing all the bulbs on that particular tail light one by one - the brake lights stayed on consistently. I have not tried removing the bulbs on the other tail light but I highly doubt the problem lies there.

I tried removing the fuse that is for the brake lights, turning signals and hazards, and they all stopped working, if that is of any help.

Lastly, I've been having intermittent problems with the boot not opening. The cables that go to the boot button from the roof of the car are not in a good condition. The boot had stopped opening the other day and I moved the cables a bit (that has fixed the issue before) and it started working again. Coincidentally (or not?) the brake lights issue started maybe the next day. Could these 2 issues be connected. From what I read, the third brake light and the other 2 side brake lights are on different circuits?

Any ideas what this could be?

 

[RUM4MO]

Hum, maybe a tricky problem, I think that you need to find out where/what the faulty wiring is probably where the wiring passing out into the hatch from the body.
Also sort out the leaking tail light cluster and make sure that the plug/socket pins are still okay and the tracks on the lamp holders are clean and not burning/conducting track to track.

Wrong bulb types can also cause problems, and the latest version of the brake pedal plunger switch, if bought from SEAT, does require to be set up correctly.

I'm guessing that when you say that the brake lights stay on even when the brake switch is removed - you mean that it is still plugged into its wiring but not mounted and compressed after initial setting up on the car.

I've had to replace a switch twice on a 2002 VW Polo, so first switch was just a slightly improved version, the next new switch was the properly revamped version. There used to be a write up on the internet covering the correct procedure when replacing the earlier improved version and a different set of instructions covering the properly later revamped pedal switch.

 

[pandasunglasses]

Hum, maybe a tricky problem, I think that you need to find out where/what the faulty wiring is probably where the wiring passing out into the hatch from the body.
Also sort out the leaking tail light cluster and make sure that the plug/socket pins are still okay and the tracks on the lamp holders are clean and not burning/conducting track to track.

Wrong bulb types can also cause problems, and the latest version of the brake pedal plunger switch, if bought from SEAT, does require to be set up correctly.

I'm guessing that when you say that the brake lights stay on even when the brake switch is removed - you mean that it is still plugged into its wiring but not mounted and compressed after initial setting up on the car.

I've had to replace a switch twice on a 2002 VW Polo, so first switch was just a slightly improved version, the next new switch was the properly revamped version. There used to be a write up on the internet covering the correct procedure when replacing the earlier improved version and a different set of instructions covering the properly later revamped pedal switch.

Thanks for the answer. I too suspect it's a wiring problem.

The brake lights stay on even with the brake light switch unplugged, not just unmounted.

I have not changed any bulbs on the car but on the one tail light I opened I found one bulb that did not light up no matter what. It doesn't look burnt out. But it didn't light up no matter what lights I turned on.

 

[RUM4MO]

Thanks for confirming that about the plugged in or unplugged brake light switch.

 

[pandasunglasses]

UPDATE:
Took the car to a garage, they swapped the BCM. They said the brake lights finally worked fine but after some minutes same thing happened, so they concluded there is a short somewhere which causes the BCM to fail.
So I guess now they will have to find the short and then find yet another BCM....
Will update the thread when it is finally fixed. Fingers crossed...

 

[RUM4MO]

What a disaster, hopefully they will find where the wiring fault or short circuit to earth is, repair that, then find another BCM and fit it and check its coding, changing the coding if necessary to suit your car!

Edit:- I'm sure that there have been cases of wiring getting sorted to earth, maybe, just a maybe, where the cabling passes over a bolt that points upwards - the bolt has a tapered end, probably to allow it to be inserted easier in the car assembly plants - and even so, or because of that feature, where the cabling passes over that bolt it can end up pressing through a or some wire's insulation. I think that this wiring is where the wiring is passed on top of a body stiffening rail at the side of the engine area. Also there might be another area where the cabling passes over a sharp edge and then gets turned.

All very vague comments I'm afraid, but maybe better than nothing, either way, I'm sure that the trouble areas are both under the bonnet areas.

Good Luck!

 

[pandasunglasses]

One thing I did not mention is that I've had the engine swapped on this car. Now that you say this about the wiring in the engine area, I am almost certain it was the mechanic's fault and that it happened because of the engine swap.

The car is currently at his garage, so hopefully he knows where he messed up during his previous work on the car.

 

[RUM4MO]

I get the impression that this fault can happen on cars that have not had their engine replaced. So really more a design or build issue.

 

[pandasunglasses]

Update 2:
Apparently they have fixed it by bypassing the circuit and creating a new one specifically for the brake lights. They also put a new brake light switch up above the brake pedal, instead of the brake master cylinder. They left the BCM as it is - they did not get a new one.
As far as I understand they are not 100% clear on what caused the problem but it is now fixed so that's what matters.