1998 xc-70 abs/tracs issues MVSOLVED - reflow solder

[Clockboy]

So for a long time the abs/tracs lights were on. Once I started working on the car myself, thanks to Boston University, I found this forum and used it to solve the problem. I tested and re-soldered the module as instructed and all was ok for about 6 months. The only other repair I did that might be associated is about 1 month ago I replaced the front left axle with a usa rebuilt that went in no problem. For the last week the abs system spontaneously engages while pressing the brakes every once in a while even while driving on flat straight roads. The peddle pulsates until released and usually does not happen again. The abs/tracs lights sometimes come on and often stay off. If the lights do come on they go off again once the car is restarted and reaches 12 mph as the system rechecks itself. I do not remember this particular issue being addressed in earlier posts. The system at times seems to believe the abs is needed and does not fault and at other times decides there is a problem. I was going to check the sensors - especially the left front - for continuity, but since 99% of the problems are the module I would not be surprised. If anyone has any other thoughts please let me know.

[mika]

Check the sensor at that wheel for continuity, you got it.

Other option is to remove the module and never have ABS again.

OR, Since you already cut into your module, you cant use that for a service like Midwest ABS rebuild. Find one on ebay, I recently got one for 50 bucks new/tested (also cut into mine) and drop that bad boy in. Don't bother finding one at a yard: they will charge you for the entire price of the ABS pump

[Ozark Lee]

Do a visual inspection on the reluctance ring at the axle you replaced. I have seen the rings both come loose and have a piece break out of them on rebuilt axles. You should be able to get to the ring from behind the hub without having to remove the axle, it is tucked in a bit into the steering knuckle and the CV joint is in the way but there is typically enough space where you can at least look at things to see if something is obviously wrong.

If the ring came loose I have used epoxy to glue them back on but you will need to remove the nut on the end of the axle to slide it back (it may be a bolt on an XC, it is on a '99 but I don't know about a '98).

...Lee

[Clockboy]

Thanks for the advice. I had thought about the reluctance ring on the new axle, but did not realize they could become loose. I figured if it worked for the first 500 miles it would definitely be fine. Will take a look on Sunday. I've done both the front brakes and the driver side axle so that axle bolt is not nearly as intimidating as it once was. I think the driver side front wheel is where the problem lies, but when the abs unit was going bad it through a code for the left rear wheel sensor. I'm betting on connection to sensor or reluctance ring, but this system has fooled me before.

[Matty Moo]

You resoldered the module..... Did you reflow all of the joints? not just stick an iron on and apply solder but actually flow the joints?

95% of the modules that come through that had been repaired at home are cold soldered. The joints were never reflowed so it would be akin to just gluing the joint.

[rspi]

I usually have the problem come back when I fix it myself.

[Clockboy]

I did reflow the solder. I'm pretty familiar with soldering and understand the need to reflow all the solder, not just put a gob on top and hope it goes into the crack. That never seems to work long term.
Hopefully I'll get it sorted on Sunday. I stared at those lights for a year and finally got rid of them. They will not win.

[abscate]

Wheel sensors should check out at about 1100 Ohms +-200

I'll go all in that if the repair lasted six months, one of the joints didn't take solder right. Perfect time interval for a bad joint.

[Clockboy]

Last night the abs seemed to engage without depressing the brake pedal and the lights stayed on even after a restart. My perceived soldering skill has been severely undermined. Im thinking it is the module and will take another crack at it if the sensor tests ok and the ring seems ok. At least the speedometer is still working.

[abscate]

This is Volvo boot camp. We deconstruct you first, then rebuild you.

Good luck getting it done