03 Rendezvous ABS problems

[chuck757co]

03 Rendezvous During slow speed stops the brake pulsates like the abs is coming on. Has been getting worse over the last several weeks. No abs or traction lights come on. Dropped off at dealer and could not find what is causing it. Also contacted Buick tech support and not able to figure it out. Anyone have any ideas?

[Airjer_]

With a good scan tool you should be ably to graph all 4 signals from the ABS wheel speed sensors. Watch the signals while braking and getting the symptom to act up. Whichever signal drops out first is the problem sensor.

[3100]

- lift hood up, find fuse box, disconnect abs 10A fuse, test drive your vehicle, if pulsation continues the problem is mechanical and would blame warped rotors. When was the last time rotors were replaced or cut? Does it pulsate more on high speed braking?

[Airjer_]

You'd think the dealer would be able to solve warped rotors if it where the case.

[3100]

Originally Posted by Airjer_

You'd think the dealer would be able to solve warped rotors if it where the case.

good thinking, but it depends to whom service writer gives this to inspect. If they give to those kids that change oil and do some small staff it is possible that some of them don't know much.

But do you agree if ABS is disabled by removing the fuse, and if the problem persists that it is something mechanical?

[3100]

Originally Posted by Airjer_

With a good scan tool you should be ably to graph all 4 signals from the ABS wheel speed sensors. Watch the signals while braking and getting the symptom to act up. Whichever signal drops out first is the problem sensor.

also you would think that speed sensors would set a code, we all know how sensitive they are?

[Airjer_]

Originally Posted by 3100

But do you agree if ABS is disabled by removing the fuse, and if the problem persists that it is something mechanical?

yup

Originally Posted by 3100

also you would think that speed sensors would set a code, we all know how sensitive they are?

Nope very common for overactive abs at slow stops without codes. It happens to all makes and models. GM seem to suffer from this the most and they have several TSB's addressing this problem. Nissan seem to have this a lot as well.

[3100]

Ok I just red that this is normal occurrence.

it is called: ABS INITIALIZATION SEQUENCE

EBCM conducts one initialization each ignition cycle. This will happen when vehicle speed is greather than 10mph and brake swithc is applied. This initialization cycles each solenoid valve, pump motor and relays for 1.5 seconds to check their operations. EBCM will set code if it finds any errors

So you don't have any problems. I am surprised that tech line did not know about this.

Airjer: Thinking with lipstick really helps LOL

[chuck757co]

Thank you for all your input. The problem does not happen everytime while making a stop but has been doing it more lately. Buick technician kept the car for almost a week and took it home with him to isolate the problem and could not figure it out then. Even with Buick tech guru they could not pin point the problem. Without costing a fortune throwing parts at it, it will be a difficult fix. I was hoping someone had this problem and had a good fix for it.

[3100]

Originally Posted by chuck757co

Thank you for all your input. The problem does not happen everytime while making a stop but has been doing it more lately. Buick technician kept the car for almost a week and took it home with him to isolate the problem and could not figure it out then. Even with Buick tech guru they could not pin point the problem. Without costing a fortune throwing parts at it, it will be a difficult fix. I was hoping someone had this problem and had a good fix for it.

-it doesn't happen every time of course here is why:

The EBCM performs 1 initialization test each ignition cycle. The initialization of the EBCM occurs when 1 set of the following conditions occur:
Both of the following conditions occur:

* The EBCM detects that there is a minimum of 500 RPM from the PCM via a serial data message.
* The stop lamp switch is not applied. (this is the case when you think that it doesn't happen every time)

OR
Both of the following conditions occur:

* The vehicle speed is greater than 16 km/h (10 mph).
* The stop lamp switch is applied. (this is when you feel that)

you can tell your mechanic to hook up scan tool and to initialize this for you with a scan tool while you are driving to duplicate the same brake pedal feeling.


if there was something wrong I am sure ABS light would be there, try disconnecting abs fuse that I recommended to isolate electrical from mechanical problems. Also this is easy to conclude if this happens only once during the same trip this is normal, but if this happens more than once during the same ignition cycle (trip) then disregard this initialization sequence message.

-tell me what happens with abs fuse removed.

[chuck757co]

Thank you 3100. I did try removing the fuse and i could not get it to do it. I put the fuse back in and it happened again. It does it sometimes more than one time during each key cycle. It does happen about 7 mph though. The service writer is now saying it maybe the abs motor but he still doesnt know. I reseated the abs module connector and could not get it to do it again so i have to wait a few days and see if it comes back.