ABS Light and Control Unit

I've got a '99 528 sport wagon with about 50K miles. Recently the
ABS light started coming on after 10-15 minutes. The dealership tried
replacing one of the sensors, but found it didn't fix the problem.
They are recommending replacement of the control unit. Does this make
sense?

Thanks.

"T. Bokuden" > wrote in message
. ..
> I've got a '99 528 sport wagon with about 50K miles. Recently the
> ABS light started coming on after 10-15 minutes. The dealership tried
> replacing one of the sensors, but found it didn't fix the problem.
> They are recommending replacement of the control unit. Does this make
> sense?
>
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

JB wrote:
> "T. Bokuden" > wrote in message
> . ..
>> I've got a '99 528 sport wagon with about 50K miles. Recently the
>> ABS light started coming on after 10-15 minutes. The dealership tried
>> replacing one of the sensors, but found it didn't fix the problem.
>> They are recommending replacement of the control unit. Does this make
>> sense?
>>
> 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.

http://www.modulemaster.com/ 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.

http://modulemaster.com/bmwabsrepair.html - 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

On Tue, 05 Feb 2008 10:08:02 -0500, "T. Bokuden"
> wrote:

>I've got a '99 528 sport wagon with about 50K miles. Recently the
>ABS light started coming on after 10-15 minutes. The dealership tried
>replacing one of the sensors, but found it didn't fix the problem.
>They are recommending replacement of the control unit. Does this make
>sense?
>
>Thanks.

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

"admin" > wrote in message
...
> JB wrote:
>> "T. Bokuden" > wrote in message
>> . ..
>>> I've got a '99 528 sport wagon with about 50K miles. Recently the
>>> ABS light started coming on after 10-15 minutes. The dealership tried
>>> replacing one of the sensors, but found it didn't fix the problem.
>>> They are recommending replacement of the control unit. Does this make
>>> sense?
>>>
>> 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.

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

JB wrote:

> 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.)

"admin" > wrote in message
...
> JB wrote:
>
>> 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

T. Bokuden > wrote:
>I've got a '99 528 sport wagon with about 50K miles. Recently the
>ABS light started coming on after 10-15 minutes. The dealership tried
>replacing one of the sensors, but found it didn't fix the problem.
>They are recommending replacement of the control unit. Does this make
>sense?

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
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Scott Dorsey wrote:
> 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.

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.

In article >, admin > wrote:
>Scott Dorsey wrote:
>> 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.
>
>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
--
"C'est un Nagra. C'est suisse, et tres, tres precis."