bimmerc90

While driving my right rear brake light stopped working. All the others were ok. Bulb was ok. Took car to Benz dealership and they replaced brake light switch still nothing. Say there is no power going to brake light. They want to replace Transmission control module for over 2000 dollars. What does this have to do with the brake light? Is there any cheaper way to resolve the TCU without buying a brand new one which is exorbitantly expensive and more than the car is worth?

kajtek1

Sounds like you have never hear the word "stealership" before?
Both rear brake lights go from the same switch wire, so if one work, that means the switch works for them.
If the right wire has no power, you need to track bad connection.
3rd brake light comes from different circuit.
For emergency fix I would run extension from left light, but that will trigger bulb error, which I think you already have.

bimmerc90

So the transmission control unit has nothign to do with the brake light issue?

bimmerc90

I'm thinking both the entire tail light assemblies need to be replaced. As they age there is a lot of arcing going on and corrosion and it's bent. When I bought the car the Previous owner had the brake light holder taped in with blue tape so I think this has been an issue that has been going on for a long time.

01BlackE320

Run from that dealer as fast as you can! And don't stop at any other ones. This brake light housings are a problem. I haven't had to replace mine but my light goes out every once in a while and I have to tinker with the connections. It helps to turn the ignition on and have someone hold the brake on (or prop an umbrella or something to hold the pedal) and move the bulb socket around. Sometimes it needs to be postioned not fully rotated in place. That is probably why there was tape

kajtek1

The arcing on those cars is know problem. You will find several possible fixes on the forums.
From using aluminium foil for shimming to hard-wire the bulbs with solder.
Talking about transmission feedback, I know brake switch gives signal to computer that controls transmission, but I doubt there is reverse feedback.

Chief Wiggum

Have you taken a digital multi-meter or "test light" and determined whether or not there is voltage going to the brake light bulb socket and the connector? You might also might want to bend up the tab and clean the contacts in the socket. The bulb twists and locks into the socket, so over time it might have corroded and/or the tab has bent down and no longer making contact. Mine happened on my left side brake light socket. I also lightly sanded the base of the bulbs to ensure a better contact.

Russell Ormerod

Find another dealer. They stupid! Most likely the contacts. Don't run wires from left to right it can damage the bulb failure module.

bimmerc90

Considering replacing both tail light assemblies completely.

Chief Wiggum

Why don't you check and see if there is voltage on the circuit before just throwing money at it?

bimmerc90

Dealership stated there is no power going to right brake lamp apparently. Fuse probably went out. I think the issues lies in the bulb holders and the contact and maybe even the type of bulb being used.

Chief Wiggum

Have you tried taking the bulb and socket from the driver's side and switching it with the passenger side? And vice versa. Depending on the dealership you're dealing with, they may or may not want to invest the minimal amount of time to test that for you. I had a friend who had the reverse light socket go bad, which I was able to find cheap on eBay.

bimmerc90

The dealership is Feldmann Imports in Bloomington, MN. They told me replacing the brake light switch would fix the problem. Since only one bulb failed that made no sense since generally when the switch fails no brake lights are operational. Anyway, I let them go ahead and do it- no dice. Then they tell me how the transmission control unit is covered in transmission fluid due to some seal on the tranny being bad. As to how that has anything to do with brake light functionality I have yet to understand. They wanted nearly 2,000 dollars for a new TCU. Absolute insanity.

Chief Wiggum

Not knowing your skill set using a digital multi-meter, I'd recommend going to a car audio shop and having them check it out for you. They can check the circuit, bulb, and socket for you for a reasonable fee. I'd also see about getting a refund for the brake switch, as if the switch were bad, none of the brake lights would work. A transmission module is not going to effect one tail light. There should be a Tint World or Mach 1 Car Audio in your area. You other option would be to go to an independent auto repair center or auto electric shop. Regardless, Feldmann's Import is definitely a place you want to avoid.

kajtek1

The brake switch has 2 circuits. One operates the lights and other gives signal to computer and I think the 3rd light is also operated from this one.
Anyway, the switch definitely was not a problem and good luck on getting the refund.
Now what come up, your pilot bushing leaks and ATF went up to computer. That sooner or later will start shortening transmission controls, so get new bushing and clean everything ASAP.
1000's topics covering the procedure.

fabbrisd1

On the tranny thing - yes, the origina transmission adapter plug on the tranny leaks internally, which in turn leads to tanny fluid "wicking" up the harness to the Tranny Control Module in the engine compartment. Take heart - the genuine MB (or MOPAR Crossfire) replacement adapter plug is like $14 - and a bottle of $9 spray MAF cleaner - replace plug - pull TCM board - hold on edge - spray on both sides - let MAF spray "run off" the board taking contaminants with it - let air dry - no heat - and reinstall - no worries.

On the brake light - yes the inner conductor/plate/board on the light assembly - and "sockets" can get tricky - "usually" a bit of patient work - checking for correct bulb - fresh socket, a bit of sanding/polishing - and a bit of prayer - can get you back up and running. So you know - aftermarket replacement tailight assemblies are sh*t - can get a bit of a search for correct/usable replacement tail light assembly.

Keep the beat !

bimmerc90

I got the car back. Checked brake fuse located in fuse bank on dash next to driver door. Fuse was burnt out. Replaced brake fuse, still nothing. I just don't understand what happened to the brakes. Makes no sense. It's gotta be the circuit boards and housings themselves.

fabbrisd1

On the brake light - yes the inner conductor/plate/board on the light assembly - and "sockets" can get tricky - "usually" a bit of patient work - checking for correct bulb/correct bulb pin position on the bulb - replace bulbs in "pairs" both sides at the same time -fresh bulb holder - a bit of light-sanding/polishing around each socket contact on the plate - and a bit of prayer - can get you back up and running. So you know - aftermarket replacement tail light assemblies are sh*t - can get a bit of a search for correct/usable replacement tail light assembly.