ABS Light and Control Unit

The recorded fault code will tell them which sensor is faulty or indeed if it is in fact a control unit issue. Most likely it will be the wiring or a connector problem if it's not actually a sensor failure.

JB

The recorded fault code is SUPPOSED to tell them if a sensor is faulty - but when these boxes fail (and they do with some frequency) - the failure is often it thinking a sensor is faulty when it isn't. Most dealerships spend lots of time and your money replacing perfectly good sensors.. and finally realize the brain is bad and replace it.

There are several places that rebuild these brains - and claim to higher standards than a new one from BMW. The advantage to this is you don't have to get the rebuilt brain coded to the vehicle as you would with a new one (and that costs $100-200 for the mechanic to do it with the GT1). If you send yours in for a rebuild - it returns coded as it was when it left, ie - plug and play.

is the one most people use - and have had excellent experience with. The ABS/DSC brain can be removed from the vehicle - and the vehicle will remain operable - but it won't have speedo/cruise-control/ABS-DSC functions until the module is replaced. The brakes will work as usual - but without ABS. - they charge $300. BMW gets about $1,000 for a new module - plus it needs programming to the car. There are other places advertisting this service - just Google "ABS BMW Repair" and they'll turn up. I only have experience with Modulemaster. Others may be just as good or simply awful - I don't know.

HTH

The computer diagnostics on the ABS unit itself is rather vague if the ABS module has failed. Depending on the ABS unit in your car it might be possible to replace just the elctronics and not the valve body with the onboard pump. I also have a 99 model and it came with ABS and ASC+T and that combination has the replaceable electronics module. It separates from the valve body with 4 Torx screws and can be replaced in just a few minutes. You do need the BMW diagnostic computer to CODE the module for proper function. If you can see the ABS component look to see if the wiring connection is round or rectangular. The rectangular unit has a replaceable electronics module, the round connector does not. The dealer wanted $2000.00 to replace everything but I only spent about $500.00 for the electronics module.

Good luck

RJD

When all they really need to do is stick a 'scope on each sensor. The waveform will tell you all you need to know.

JB

You're confusing mechanics with electronic technicians. They would be clueless without the GT1 - and the GT1 doesn't do scope functions. (And there would only be a waveform if the wheels are turned - another challenge to the average mechanic.)

I must stop making these wild assumptions that dealer techs actually have that seemingly rare attribute, common sense, and the aptitude/skills for true diagnostics. :>)

JB

It might, but it would depend on what error codes they are getting out of the unit.

The dealership SHOULD have a spare ABS control unit that they can swap in, verify that it fixes the problem, and swap back out if it doesn't fix the problem. If it happens consistently after 10-15 minutes it should not be hard to find.

I know some of the ABS control units in the late eighties were prone to cold solder joint issues but I don't know about anything as new as the '99.

--scott

Not that simple - the ABS/DSC control unit is keyed to the vehicle. Once keyed apparently it can't be reused on another vehicle. No way to have a unit that can be swapped in and out.

Sheesh, were they doing that as early as '99? That's evil.

--scott

It is - but the same module is used on multiple models and series - so this way they know it has the correct settings for your car's configuration.

That's why getting it rebuilt at someplace like ModuleMaster is a much better deal. The module comes back to you with the factory coding still set for your car. That avoids having to buy a new blank module and get it coded by BMW at a few hours labor.