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Brake lights coming on when car is OFF, key OUT

25K views 16 replies 12 participants last post by  Roverlander117 
#1 · (Edited)
My brake lights are coming on and staying on at random when the car is OFF, with the key out. When I turn the key and start the car, they turn off and go back to working normally, i.e. turning on only when the pedals touched, etc. But the minute I turn it off, there is a good chance they come back on, usually immediately. So I'm thinking, they are getting shorted and getting power from some other source, maybe an exposed cable. But I go to the fuse box and pull each fuse out one at a time to see if they go off, and nothing. They stay on through the whole process. So, evidently they are getting power from somewhere before the fuse box. We located the power cable running from the trunk to the fuse box, and all the wires that run along with it. Jiggling the whole length of the wire, the lights never flicker, never go off. So now I am totally lost. No idea where they would be getting power from. Maybe something to do with my light switch control center? Which I have no idea of the location of, I just saw it in my Chilton book as something with a boatload of light wires that might be the center of the problem.

I have already replaced the brake light switch, it was the first thing I did, again no luck

Any help at all?
Thanks

EDIT: I have a 2001 325 Ci, Sport
Also have sub amp in the back around the battery, but have taken it completely out the equation, no luck
 
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#2 · (Edited)
I would start by checking the brake light switch attached to the brake pedal. If that doesn't work I'd be looking at the ground wire pins as they were an issue and BMW issued a recent recall for it on some models, not the 01's though (I don't think).
 
#5 ·
On a rare occassion I have walked away from my car only to notice that ONE light was lit up... Car off... Key in my pocket.... Looks like a brake light, but only on one side. The problem was, when I get out my car I may hit the blinker. If it is in one of the turning positions, the light will stay on. Not blink, but stay on... Even if you leave your car for hours.. Not saying that is the problem, but it could be a good place to start looking. When it looks like your brake lights are on, check the front turn signal to see if it may be on too..
 
#12 ·
First off I would suggest short to ground somewhere.

But did you use a genuine BMW OEM switch?

You need a genuine BMW brake switch. The aftermarket ones don't work.
The genuine switch is two switches in one. One of them is used to switch the lights on and off.
The other is used by the light control module (LCM) to test the brake circuit.
The aftermarket switches don't have the test switch so the LCM thinks the circuit is faulty
and leaves the brake lights on as it should do as directed by the LCM emergency response
mode program. Be sure to compare the design of the switches. Even when you type in the
BMW part number into Google you still get the aftermarket switches because the sellers
don't know sh*t about these switches. The BMW switch is shorter than the aftermarket switch
and the serrations are on opposite faces.

There may be other issues associated with teh aftermarket switches that I'm not aware of.

So if you bought aftermarket replace it with a genuine BMW one.
 

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#13 ·
First off I would suggest short to ground somewhere.

But did you use a genuine BMW OEM switch?

You need a genuine BMW brake switch. The aftermarket ones don't work.
The genuine switch is two switches in one. One of them is used to switch the lights on and off.
The other is used by the light control module (LCM) to test the brake circuit.
The aftermarket switches don't have the test switch so the LCM thinks the circuit is faulty
and leaves the brake lights on as it should do as directed by the LCM emergency response
mode program. Be sure to compare the design of the switches. Even when you type in the
BMW part number into Google you still get the aftermarket switches because the sellers
don't know sh*t about these switches. The BMW switch is shorter than the aftermarket switch
and the serrations are on opposite faces.

There may be other issues associated with teh aftermarket switches that I'm not aware of.

So if you bought aftermarket replace it with a genuine BMW one.
Hi Ray, lights still on. I need to gety my diagnostics software working again. What are you using to get the error codes?
I replace ignition switch which needed doing as had reached end stop so difficult to start and replaced brake pedal switch now but lights staying on.
 
#15 ·
I found this thread because my 2005 BMW Range Rover started doing the exact same thing: brakes lights stuck on when key is out.

This unwelcome phenomenon occurred after rain water went down the interior of my A pillar and splashed the LCM (light check module / light control module)…

I also have a 2002 530i with the same model LCM, so I can swap them. My brake lights do not stay on with the 530i LCM. (But of course, the 530i's has a blinker stuck blinking, after it was jumpstarted one times too many.)

These LCMs have 3 cable bundles. When I unplug the side black plug (where the pinout claims the brake lights run through), the brake lights turn off.

I've just ordered new LCMs off eBay for both cars…

Here's an excerpt from the Electrical Library PDF for the Range Rover:

NOTE: The lighting circuits are not protected by conventional fuses. Metal Oxide Semi-conductor Field Effect Transistors (MOSFETS) within the Light Check Module (LCM) protect the lighting circuits. For more information, refer to the Lighting section of the System Description and Operation Workshop Manual.
Here's what the System Description and Operation PDF says:

Circuit Protection
Operation of the lamps is performed using overload proof Metal Oxide Semiconductor Field Effect Transistors (MOSFETs). The MOSFETs have a diagnostic output for bulb monitoring and can detect overload, load interruption with the lamps switched on and short circuit to positive with the lamps switched off.

The MOSFETs are protected against short circuits, removing the requirement for the lamps circuits to be protected by fuses. The MOSFETs respond to heat generated by increased current flow caused by a short circuit. Normally this would cause the fuse to blow. The MOSFETs react to the heat increase and cut the supply to the affected circuit. Once the fault has been rectified or the MOSFET has cooled, the MOSFET will automatically reset and operate the circuit normally.

If an overload occurs, the current flow is dependant on the temperature of the related MOSFET and can be up to 20 times the rated current of the lamp. The MOSFET heats up and deactivates the load applied to the circuit. When the MOSFET cools the circuit is once again reactivated. This thermal cycling occurs continuously in the event of an overload occurring.
That would explain how the LCM is bypassing fuses and getting electricity: one of its 'MOSFETS' must be messed up.

Fortunately, my 2001 E46 convertible does not seem to have LCM issues. The RR (and 530i?) are known for having interior water issues from blocked sunroof drains, but since the E46 LCM is attached to the light dial/buttons, I'm not sure if it can get water damaged so easily? But that's where I'd start investigating.
 
#16 ·
I found this thread because my 2005 BMW Range Rover started doing the exact same thing: brakes lights stuck on when key is out.

This unwelcome phenomenon occurred after rain water went down the interior of my A pillar and splashed the LCM (light check module / light control module)…

I also have a 2002 530i with the same model LCM, so I can swap them. My brake lights do not stay on with the 530i LCM. (But of course, the 530i's has a blinker stuck blinking, after it was jumpstarted one times too many.)

These LCMs have 3 cable bundles. When I unplug the side black plug (where the pinout claims the brake lights run through), the brake lights turn off.

I've just ordered new LCMs off eBay for both cars…

Here's an excerpt from the Electrical Library PDF for the Range Rover:



Here's what the System Description and Operation PDF says:



That would explain how the LCM is bypassing fuses and getting electricity: one of its 'MOSFETS' must be messed up.

Fortunately, my 2001 E46 convertible does not seem to have LCM issues. The RR (and 530i?) are known for having interior water issues from blocked sunroof drains, but since the E46 LCM is attached to the light dial/buttons, I'm not sure if it can get water damaged so easily? But that's where I'd start investigating.
You might also have to synchronise the mileage recorded in the LCM so that it is the same as the mileage
recorded in the display otherwise you will see a small dot next to the mileage on the display.
It's refered to as the tamper dot. But only if it bothers you.
 
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