Hi all, I'm looking for a bit of help and advice, I have a skoda Octavia estate 1.9tdi 4x4 2006 (55) plate, when I start the car, the brake lights are staying on, I can disconnect them from the lights and reconnect them and they stay off and work as normal. This only happens when I start the car,  whatever the problem is, its draining my battery as put new one in and 3 days later its flat. I have changed the switch, which for my year, was in master cylinder in engine, I have changed the battery and bulbs. 

This problem is the only thing stopping me from getting it mot'd and I really appreciate any help or advice to solve this issue. 

Also check the brake pedal operation and switch.

 

I believe a tired battery is the root of many electrical gremlins.

 

The theory being, when cranking the engine, the battery doesn't have enough in reserve to keep the electronics properly supplied.

 

This power brownout can corrupt some of the data giving problems like the one you've experienced, necessitating a reboot if you like by disconnecting the battery, turning ignition and hazard lights on to completely discharge the system,  then refitting a new or recharged battery to prevent reoccurrence of problems.

Are you sure that there is not a second brake switch on the pedal as well, often the engine management and cruise control use a seperate switch, if the one on the master cylinder has only 2 wires = 1 pair of contacts I would bet there is an additional switch.

 

To rule out the master cylinder reed switch and possibly a sticking magnet on the piston assembly disconnect it and see what happens, the contacts should be open circuit, also when its in position until the brake pedal is pressed.

 

Some have reported that a problem with the high level rear LED brake light has caused similar issues, are all the LEDs working correctly on yours?

 

The last port of call is the Body Control Module, might be called Comfort Control Module or Central Electric Module on your car.

 

Have a VCDS scan done if you can, if its a switch it will bring up an implausible signal error code, if its the module it may say something like incorrectly coded or communication error.

21 minutes ago, MicMac said:

Also check the brake pedal operation and switch.

 

I believe a tired battery is the root of many electrical gremlins.

 

The theory being, when cranking the engine, the battery doesn't have enough in reserve to keep the electronics properly supplied.

 

This power brownout can corrupt some of the data giving problems like the one you've experienced, necessitating a reboot if you like by disconnecting the battery, turning ignition and hazard lights on to completely discharge the system,  then refitting a new or recharged battery to prevent reoccurrence of problems.

 

Thank you for your help and advice and I will try the reboot as I've not done that yet, put new battery in but within 3 days it was drained and wouldn't start the car but will get it sorted out and charge it up. Again thanks for taking the time to reply and for advice 👍

The switch you changed had 4 wires, right? 

My mistake, 4 wires.

Edited 26 February, 20224 yr by MicMac

1 hour ago, Pete_Ex-Wino said:

The switch you changed had 4 wires, right? 

I dont know as it was garage who changed the switch, they said they had to eventually put a genuine part in. My switch is not at the pedal but it's in the master cylinder in the engine, there is a space at pedal for the switch but no connector/wires to connect to 

2 hours ago, J.R. said:

Are you sure that there is not a second brake switch on the pedal as well, often the engine management and cruise control use a seperate switch, if the one on the master cylinder has only 2 wires = 1 pair of contacts I would bet there is an additional switch.

 

To rule out the master cylinder reed switch and possibly a sticking magnet on the piston assembly disconnect it and see what happens, the contacts should be open circuit, also when its in position until the brake pedal is pressed.

 

Some have reported that a problem with the high level rear LED brake light has caused similar issues, are all the LEDs working correctly on yours?

 

The last port of call is the Body Control Module, might be called Comfort Control Module or Central Electric Module on your car.

 

Have a VCDS scan done if you can, if its a switch it will bring up an implausible signal error code, if its the module it may say something like incorrectly coded or communication error.

Thanks for taking the time to reply to me, the high level light is on when boot lid is up but goes off when boot shut, I have done a vcds on the car and everything seems fine. It's a bit of a puzzler and really hoping it's not ECU hence trying all I can just now. 

Again thanks for taking the time to reply and to help me, its much appreciated 

16 minutes ago, rfindlay said:

I dont know as it was garage who changed the switch, they said they had to eventually put a genuine part in. My switch is not at the pedal but it's in the master cylinder in the engine, there is a space at pedal for the switch but no connector/wires to connect to 

It will have 4. It's a hall effect sensor integrated with two 'virtual' switches to simulate the old pedal type.

Check cabin fuse no.2 (5 amp), if your engine code is AZV or BKD. If it's neither of those, what is it?

49 minutes ago, Pete_Ex-Wino said:

It will have 4. It's a hall effect sensor integrated with two 'virtual' switches to simulate the old pedal type.

Check cabin fuse no.2 (5 amp), if your engine code is AZV or BKD. If it's neither of those, what is it?

It's a bit of a mystery lol, I had auto electrician out looking at it and after hour and half, he thought it was the battery which was always getting drained so got new battery but still no change. Thanks to everyone here who has replied and got couple of more ideas to try, I don't want to give up on this as car is in very good condition and it's the only thing stopping mot. 

The behaviour of the high level brake light as you described it is suspect.

 

Within VCDS you can cycle the brake lights using the output tests, this is sending a command to the BCM/CCM/whateveristcalledtoday to apply voltage to the bulbs & high level LED, this will test if the module does what it should if it gets the right input from the brake cylinder switch. Pay attention to the operation of the high level light, I don't understand how it could screw things up but there have been reports that it does.

 

You could also try disconnecting it.

The whole brake lighting system seems somehow inverted, reboot the car following my instructions and recheck its operation.

Edited 26 February, 20224 yr by MicMac

How was the fuse?