The latest addition, a 1996 850 sedan, came home with the Tracs light on and the ABS light is burned out. It makes me think it had been that way for a while. For grins I decided to try a do it yourself fix and it apparently worked.
The obvious first step is to find an E-5 Torx socket. If you have an O’Reilly Auto Parts in your area they can get you one quickly. Virtually no store stocks them but they do stock them in the warehouses. I ordered one by phone at 9:00 AM and it was at the nearest store by 1:30 PM, US $2.99 plus tax. It is a Lisle part number 26770.
The process at the car begins with removing fuse number 14 from the fuse box and then disconnecting the power connector and the signal connector from the ABS module. It is easiest to remove the signal connector first which is done by depressing the catch and lifting the connector shell straight up, The connector hood hinges and this releases the connector. If the car is to be driven while the module is being repaired it would likely be a good idea to wrap the connectors in a Baggy and to secure the connectors away from things that get hot.
Here are the release points.
The next step is to remove the four Torx bolts that secure the module to the pump/modulator assembly. In my case with an normally aspirated engine I found that removing the air heater pipe from the airbox gave me much more room. Three of the four bolts come out easily but the fourth bolt, lower front, is largely blocked by the throttle cable. I found that putting the ratchet below the throttle cable worked the best.
Once the torx bolts are removed and set aside the module is removed by dropping it an inch or so to clear the solenoid plungers.
Here is the removed module.
The next step is the hard step. Clearly they don’t want you to open the box. It has the press on retainers around the posts and the entire box has a silicone seal. The press on retainers were very corroded and rusted around the posts and after futzing with them for 20 minutes or so I just fired up the Dremel tool with a cutoff wheel and sliced through each of them and removed them. I then tried to release the silicone seal by using a small screwdriver and raking it vertically between the lid and the base, pulling the silicone out from between the top and the bottom housings. I was trying very hard to keep all of the plastic intact but I was unable to do so. In the end I might have been better off scoring the whole outer lip of the lower housing away with the Dremel tool from the start. After much scraping, prising, and breaking of the lower lip I was able to remove the top off of the module.
Here is a picture of the attempts to pull the sealant away from the respective halves of the cases.
Once inside, the circuit board is revealed. The circuit board is covered with a clear silicone like membrane over its entirety. After much research I have learned that the failure point on the modules is the solder joints on the connectors, particularly the power connector. In order to see and assess the solder joints it is necessary to remove the protective membrane from the circuit board in the areas that you want to solder. This is easily accomplished by slipping the tip of a knife under the membrane at the edge of the circuit board and lifting it off.
Here are some pictures of the PC board with the membrane partially removed.
The solder joints that usually go bad are circled here.
From here it is a matter of re-soldering the joints. The power pins are obviously solid as they act as a large heat sink. I think this is the root problem with the modules from the factory. The pins themselves need to be heated quite a bit in order to get the solder to flow properly between the pins and the pad on the PC board. I used a 40 Watt soldering iron and laid on the pin for a good couple of minutes each in order to preheat the pins and then added solder. I left the iron in place until the solder flowed. I was somewhat worried about keeping that much heat on the pins and possibly damaging the circuit board traces but the pins are a large enough heat sink that the board can take a lot.
Once the joints are soldered it is a matter of resealing both the circuit board and the case. I had a tube of black, pure silicone, sealer and I gobbed a bunch of it on the PC board where I had removed the original protective membrane. I then put a generous bead around the edge of the lower housing and pressed the two together. More silicone than I used would have made the job look prettier but it certainly looks well sealed from the elements.
From here it is a matter of allowing the silicone to dry and re-installing the module.
In my case I fired up the car and the Tracs light came back on but it went out immediately after I took off up the street. I think that, if I had an operating ABS light, it would have gone out as well.
While I’m sure Victor and the other rebuilders have better tricks, this was something I could do myself and paying for half of the 140k timing belt job - slated for next week - in savings doesn’t hurt either.
Last edited by Ozark Lee
on 21 Oct 2008, 20:28, edited 2 times in total.
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