# HELP! Brake Booster Control Module J542 - What is it?



## hobhancock (Apr 17, 2006)

Hello all

I am trying to understand what is this brake booster control module. I have a 2002 Jetta 1.8T tiptronic that has a hard brake pedal. I also get a code 17837. I have tried a number of things. I have another Jetta with the same setup that I have been stealing parts to help fix the issue. In the bentley manual in the schematic pages, it lists this brake booster control module J542. The Ross-Tech site suggests when one gets the code 17837 is to change the brake booster control module. I do not know what they are referring to. Is this the brake vacuum pump located under the car on these automatic?. So this is what I have done so far;

Swapped brake booster
Swapped master cylinder and ABS pump
Swapped brake vacuum pump
Bled the lines the old fasion way as well as with VAGCOM.

Complicating the problem could be the fact that I dont know if the parts I am swapping are any good. How does one test the brake vacuum pump off the car? In the measuring blocks within VAGCOM, it does show the pump is turning on. I should get under there and hold it in my hand while someone pushes the brake with the car running to see if I feel it turn on.

I am going to test the vacuum pressure today. I assume my targets will be in the bentley manual. This car is just not safe to drive when you need both feet on the pedal to stop it. I hope someone out there can shed some light on this issue.

Thanks so much


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## hobhancock (Apr 17, 2006)

*Update:*

I now think I have this figured out and hopefully it can be useful for anyone else. The brake booster control module is the module that is intregrated into the vacuum pump itself. I finally was able to figure out how to test the pump to see if it works out of the car. I apologize, but I cant remember where I saw another poster explaining how to do it. What you do is this. The pump module has three prongs in the connector. They are labeled 1,2,5. You need to ground 1 and 2 and apply 12 volts to pin 5. My pump just clicked, but when the new one (used from the junkyard) came I tested it and confirmed that it does run. I installed everything back with much excitement to finally have this work the brakes like it should. That was short lived, because it only helped some what. I could tell there was a difference, so I knew I was headed in the right direction. This made be believe that I was getting vacuum upon startup, but then would lose it. I figured I must have a leak somewhere. I believe my connection with the check valve that is between the booster and the intake manifold was where I was losing it. I fixed that and took it for a test drive. I believe I got it. I have driven for the past two days without issue and have a good brake pedal. Keep in mind also, that there are two check valves, one between the vacuum pump and the booster and then between the booster and the intake.

I hope this will help others down the road.

Reminder. The car is a 2002 Jetta 1.8T automatic with the EYN (tiptronic) tranny or automanual. You access the pump from under car. It sits up in a cubby hole just behind the rack and pinion on the drivers side. It is somewhat of a pain to get it. The pump is mounted to the bracket with two 10mm bolts. You have to take those out in order to remove the bracket so the pump is more accessible. Once the bracket is out, you can move the pump in a way to reach the clamp that holds the hose on the vacuum pump that goes up to the booster. This hose goes into a T connection which plugs into the hole in the booster then continues on to the intake manifold. I was told that this pump only comes on the automatics, however a guy that runs one of the local junkyards said he has a few automatics but he said his cars did not have the pump. So it made me wonder if they are only on the 1.8T automatics with the EYN tranny. I dont know for sure. When he said he had a few 2002 autos and they didnt have a pump, thats what I concluded. Dont take my word for it.


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