tech007

Hi everyone,
I have a 05 ML350 special edition with no brake lights. I have replaced the pressure switch on the bottom of the master cylinder and still no brake lights. There are no indicator lights lit up in the dash panel, the fuse is okay, and I have swapped the relay around but still no brake lights. A jumper across the brake light relay will make them come on so I know there is no problem in the back. I have read a lot of the other post and most indicate that there are some indicator lights on in the dash panel or the brake lights stay on all the time. Also, most of the issues link back to the ABS pump. I have been told that there is a switch inside of the brake booster that cannot be serviced but the booster must be replaced that will cause the brake lights not to work.
Does anyone have any ideas as to the nature of my problem.
thanks,
Tech007

art_arev

Scan the car with a pro level scanner & post the codes

tech007

I got a scanner and scanned for codes and ABS codes. There were no stored codes nor pending codes. As I stated earlier,There are no lights on in the dash panel nor are the brake lights constantly on. When I scanned the system vehicle w/vehicle running, the bas,esp,ets,and brake lights on the dash illuminated then went off. After the scan was complete it indicated that there were no fault codes. Where do I go from here????

Maj. Dundee

What is the name and model number of your scanner?

tech007

Hello
The scanner is a Cen-Tech OBDII/EOBD + ABS scanner.

Maj. Dundee

I still do not understand why there are no codes and why no lights are illuminated in the cluster.

Are you absolutely positive your scanner can read ABS codes, which start with the letter Cxxxx?

Do you have a test light?

tech007

Yes the scanner will read ABS codes and I thought it weird that there are no dash lights on and that is why no one had noticed that the brake lights were not working. One day a friend was following the car and noticed no brake lights at stopping points. I do have a circuit tester too. I had replaced the brake light switch on the master cyclinder but would like to know if there is a non-servicable one inside the brake booster that will cause this type of problem.
The is power coming to the brake relay and I can make them illuminate with a jumper from there, so I know from there back they are okay.

Maj. Dundee

Yes there is a non serviceable release switch A7/7s1 inside the booster which causes this problem.

Can you make a video of putting the key in the ignition, turning it to pos. #2, then starting the eng. and wait till all the lights go out?

tech007

I think I may be able to do that and will give it a shot.
If the switch inside the booster itself was faulty would it possibly not show any codes or lit dash lights?? On one side of the booster is the travel sensor and the other a electrical connection. Would the electrical connection be that switch and if so, is there a way to test it.

Maj. Dundee

Did you just buy this truck?

If the switch was faulty it would set code C1201,02 or 03, but there are no tests for those codes.

On the other side of the booster is where the signal come out to the ESP/Traction control Module informing it that the pedal has been depressed and released.

Clean off those wires and tell me what colors they are.

I still say that something is very odd that there are no lights coming on in the cluster. Very odd.

Maj. Dundee

Please UPDATE YOUR PROFILE.

tech007

I looked at the plug wires you asked about and the colors are Red,Tan, Light Brownish, and blue. I have included a link to the vid of the ignition on and cranked process...hope it works okay.....had a little struggle with that.
https://drive.google.com/file/d/0BxK...ew?usp=sharing
Once it starts up the "low range" light blinks several times then stops. It has always done that for the past 7 plus years.
Question: If the plug you had in your illustration is the brake switch in the booster, is it possible to check with a OHM meter its status with the brake pedal depressed and pedal released? Also, if it is open all the time would that account for no lights on? "Just a thought"
Question: Even though they call the pressure switch on the base of the Master Cylinder a Brake light switch, what is its actual function in the chain of events leading up to the brake lights coming on?

tech007

While checking for availability of parts around me, a parts clerk said that models 99 - 2005 brake boosters were the same.

Maj. Dundee

Only buy a booster with the numbers ending in 07 08. The very earlier ones did not have ESP installed.

That plug is not the brake switch. I said that the signal is transmitted through those wires to indicate that the brake pedal has been depressed.

Again, I previously said that there are no tests for the booster problems. Testing those wires won't do you any good because you do not know what signal was transmitted when the booster was operating properly. In other words, you don't have any info to compare it to.

The part at the base of the master cylinder is not a switch, it is called a Pressure Sensor and senses the pressure of the brake fluid and has nothing to do with the operation of the Brake Lights.

Since none of the cluster lights are illuminated, the only other thing I can think of is, one of the wires at the BAS/Traction Control Module has broken.

Remove the left front wheel and fender liner and access the 48+ wire wiring harness. Strip off as much of the tape as possible and look for a corroded or broken wire. If there isn't, then the only choice you have is bringing it to the dealer or install a used booster.

Maj. Dundee

Before you buy a booster or conduct any tests that I have suggested above, please do the following.

Remove relay K6 from the fuse module and turn the key to pos. #2. Get an 8" piece of 14 ga. wire stripped at both ends.

Insert one end into slot #86 at the fuse box and with a DVOM check the other end for B+.

Insert one end into slot #85 at the fuse box and with a DVOM check the other end of the wire for B+ or GROUND. Then have someone step on the brake pedal and perform the same test.

Post results.

tech007

I followed your instructions and did the test for #86 and got a reading of 12.32 with key on and brake pressed and with key off and brake released. The power to that terminal remained pretty constant. In checking #85, I got no reading for ground in any situation. I checked that slot with the tested hooked to the positive terminal and probe to #85 for ground with no results. I hope that give you some additional information for me to work with. While awaiting your response, I am going to take the fender liner off and take a look at the wiring harness for possible problems there.
I can put a jumper across #86 and # 87 and the lights will come on, I can also touch a jumper from a positive to the Brake light fuse and the lights will come on.

tech007

Thanks MAj. Dundee & Art for your help.
As I investigated the wiring from the ESP/AbS pump I discovered one wire that was broken due to it rubbing against the plastic inner fender well cover. I made the repair to the wire and we are back in business with working brake lights now. Again, I appreciate your help and dedication to helping folks like myself keep them going. I wish more information were available for these cars b/c I don't have much on them........my attention is more on the class 8 vehicles I use everyday.
Thanks Again,
Howard

cruiser222

hi there!
Greetings from Bulgaria! Please give me an advice.
I am driving ml 270 W163 2005year and I have no brake lights.
I read carefully about tech007's experience.
The truck was connected to STAR diagnostic and it said there was no any problem.
Also there is no brake sw on the brake pedal. Cruise control is working properly. There are no mistakes with the AAM.
The bulbs were tested on a battery - they are OK, also the contacts were cleaned.
The fuse is ok
the relays are ok.

So I decided to remove the front left inner fender and the front left light. I could not find any corroded cable. Also I tried to remove the plastic connector to the ABS pump but the the water tank is too near to the connector and i could not unplug it completely. So I was only able to remove the shield around the wires. I could not find any corroded cables there.
And there are still NO BRAKE LIGHTS.

Could somebody give me any additional advice???

ILIYAN

Maj. Dundee

The first thing that you have to do is:

a. open the hood and remove the cover of the fuse box.

b. remove fuse #25 and check to see that it is not blown. If not...........

c. turn the key to pos. #2 and have someone step on the brake pedal while you test both contact at fuse #25 for 12v.