Brake lights always on?

Hi,
I having a problem with the brake lights always being on.
this happens as soon as i turn my lights on.
So i checked the brake light switch and it seemed to be working just fine. so was wondering what things i should check next?
but now iv noticed there on all the time, regardless of lights on or off?

this is all came about after my wife called the RAC a few days ago as the car went into limp mode. the car started to shudder alot and struggled to pick up any speed in higher gears.
We had the coil pack and the spark plugs changed yesterday, but the problem is still there, not as bad but still obvious enough, and ever since then the brake lights have stayed on.
Any thoughts on this?

LeeC wrote:So i checked the brake light switch and it seemed to be working just fine.

Hi LeeC,

I would double check this and even just change it. The next step is to see if the BSI is getting a signal to operate the brake lights or to see if they are on without the BSI putting them on.

Use a lexia clone like these from ebay to see what the BSI sees.

This one shows one of the many screens and some of the selection process for 'live data' on the brake pedal input

The lexia topic is here, which may help if you are thinking of getting one

Hi thanks for the suggestions,
I have tested the brake light switch this morning and seems to be functioning OK. It only when I turn the car headlights on it turns the brake lights on. I've checked all the fuses (even though it can't be them if they have power) and they are all good.
So sounds like an electrical fault.
Possibly a relay?
I read somewhere about reseting the BSI so I might try that to see if it changes anything.

LeeC wrote:Hi thanks for the suggestions,
I have tested the brake light switch this morning and seems to be functioning OK. It only when I turn the car headlights on it turns the brake lights on. I've checked all the fuses (even though it can't be them if they have power) and they are all good.
So sounds like an electrical fault.
Possibly a relay?
I read somewhere about reseting the BSI so I might try that to see if it changes anything.

The BSI is the control unit for lighting, but the BSM (engine bay fuse box) also has a hand in lighting. There are no classic relays you can unplug and replace for the lights, but rather solid state control chip inside the black boxes that are the BSI and BSM.

It will be good to hear how the BSI reset goes.

https://citroenc3owners.com/citroen-c3-t ... 3-t69.html


There could be a fault in the rear cluster. They are not too difficult to remove, maybe take them out and check the lamps and the connectors?

https://citroenc3owners.com/citroen-c3-t ... -t621.html

BSI reset didn't solve anything so I'm stumped.
Going to buy a replacement brake switch just in case it's faulty although it seems OK.
It's annoying as my wife cant drive it being dark when she gets out of work in the evening.

LeeC wrote:this is all came about after my wife called the RAC a few days ago as the car went into limp mode. the car started to shudder alot and struggled to pick up any speed in higher gears.

You will have to diagnose this with an obd tool, looking for fault codes, lexia is the all singing and all dancing tool, but a cheap OBD reader may give you enough to go on to diagnose the fault with the engine running.

LeeC wrote:Going to buy a replacement brake switch just in case it's faulty although it seems OK.

How did you test the switch?

I tested the switch by disconnecting it and taking the switch out from the foot well, then plugged back in and pressed it manually whilst checking the lights in the reflection of a window.

So this evening I took the rear drivers side light cluster off and removed the brake light bulb. And it all worked fine again? So I have left the bulb out for the moment and will just drive it with the left and top break light both working.

I changed this bulb about 2 weeks ago because it was out, I then tested it and everything worked fine, so the problem must of occurred since then.
Do Citreon use a particular type of bulb? Maybe the one I replaced was to high (or low) in watts?

Anyway I have ordered an OBD reader to try and diagnose the problem with the engine losing power etc but for the meantime it's driveable.

I'd have a careful look at the replacement bulb you fitted, I suspect it's the incorrect type. There are quite a few bulbs that look similar but are slightly different. Usually there's a letter on the end of the bulb reference, this indicates things like filaments and connections on the bottom of the bulb. The different types have the pins on the side of the base placed differently, some types have the pins offset, both around and up and down the base. The idea of this is to prevent the wrong bulb going on the holder, however, in practice holders aren't precision made items and the wrong bulb will fit without too much effort.

I've had a similar problem, brake lights stuck on, but not always, sometimes days without trouble, replaced the brake light switch twice, checked everything you've mentioned. In the end I suspected a short circuit, frayed wire somewhere supplying power to the brake light circuit after the brake light switch, so I followed the wires on from the switch under the dash and along the inside of the door sill to under the passenger seat where there's another junction box with several connectors. I moved the wires around and the brake lights went out and work normally now when I put the pedal down only. One day I'll get round to looking for the actual frayed wire, for now I'll keep things like water bottles from rolling around under the passenger seat and bumping into the wires