I am having a problem with ABS brake system.
Please chime in if you have direct knowledge towards resolution. Last Spring while at a RED light, foot on the brake the car lunged forward a few feet. It was like I stepped on the gas while my foot was on the brake… The best way I can describe the feeling is imagine you are on a wet road and apply your brakes hard… the petal pulsates rapidly (ABS engaged). I get this feeling while not in motion and the car groans and moves forward on its own. The only way to stop it is to release the break or engage the parking brake. After it does this I get the Xmas lights related the EMCV failure. If I cycle the car the problem most times goes away but I am now always cautious at lights or behind other vehicles.
I posted the problem on the board and got many posts referring to me accidently pressing the gas which was total not the case. (not everyone here has something positive to post but feel they must be heard)
A couple days later I had the same problem while backing out the garage so I took to the dealership. They were able to see the problem first hand on their back lot, service rep drove and I watched as it jerked him around. Four days and $600 in labor later I was told it was resolved and it was for a few months, now the problem is back. Hesitant to return to dealer as I don’t feel they don’t now what the problem is and I don’t want to pay for anymore exploratory labor.

In 2006 the EBCM, BPMV replaced.
In 2007 the wire harness to the TAC was repaired (not replaced) as dealership stated it was sliced, they also replaced two front speed sensors replaced.

Only 4500 miles since 2006.

Here are the codes I am getting;

28-TCS - Traction Control System
C1225 RF Excessive Wheel Speed Variation
C1226 LF Excessive Wheel Speed Variation
C1227 LR Excessive Wheel Speed Variation
C1228 RR Excessive Wheel Speed Variation

B0-RFA - Remote Function Actuation
U1016 Loss of Communication with PCM
U1064 Loss of Communication with BCM
U1096 Loss of Communication with IPC
I have clear the grounds under the hood, are there other grounds I should clean and/or should the rear speed sensors be replaced?
Thanks

 

ttt

 

The codes you are getting show up when the brake pedal isn't being pressed and will deactivate the ABS. Here is the diagnostic info for the left front:
DTC C1225 LF Excessive Wheel Speed Variation

Circuit Description
The speed sensor used on this vehicle is a single point magnetic pickup. This sensor produces an AC signal that the EBTCM uses the frequency from to calculate the wheel speed.

Conditions for Setting the DTC
The DTC can be set anytime the brake is not depressed and no wheel speed sensor hardware DTCs are present, and the EBTCM sees a wheel speed variation of more than 14 Km/h (9 mph) for 2.5 seconds.

Action Taken When the DTC Sets
ABS/TCS/Active Handling (if equipped with RPO JL4) are disabled.

Indicators that turn on:
ABS indicator
Car Icon (TCS indicator)
Messages displayed on the DIC:
Service ABS
Service Traction System
Service Active HNDLG (if equipped with Active Handling RPO JL4)
Conditions for Clearing the DTC
Condition for DTC is no longer present and scan tool clear DTC function is used.
Fifty ignition cycles have passed with no DTCs detected.
Diagnostic Aids
It is very important that a thorough inspection of the wiring and connectors be performed. Failure to carefully and fully inspect wiring and connectors may result in misdiagnosis, causing part replacement with reappearance of the malfunction.
An intermittent malfunction can be caused by poor connections, broken insulation, or a wire that is broken inside the insulation.
If an intermittent malfunction exists refer to Testing for Electrical Intermittents in Wiring Systems.
Test Description
The numbers below refer to step numbers on the diagnostic table.

Step 3. Checks the resistance of the WSS.

Step 5. Checks if the WSS CKTs are shorted together.

DTC C1225 LF Wheel Speed Sensor Input is 0 Step
Action
Value(s)
Yes
No

1
Was the Diagnostic System Check performed?
--
Go to Step 2
Go to Diagnostic System Check - ABS

2
Inspect the WSS wiring and connectors for damage.
Inspect WSS for looseness or damage.
Is physical damage of sensor evident?
--
Go to Step 7
Go to Step 3

3
Disconnect the WSS at the sensor pigtail.
Using J 39200 DMM, measure the resistance between terminals A and B of the WSS.
Is the resistance within the range specified in the value(s) column?
850-1350ohms
Go to Step 4
Go to Step 7

4
With J 39200 DMM still connected, select the mV AC scale.
Spin the wheel as fast as you can by hand while monitoring the AC output.
Is the AC voltage within the range specified in the value(s) column?
Above 100 mV
Go to Step 5
Go to Step 7

5
Disconnect the EBTCM harness connector.
Install J 39700 Universal Pinout Box using the J 39700-25 cable adapter to the EBTCM harness connector only.
Using J 39200 DMM, measure resistance between terminals 15 and 31 of the J 39700 .
Is the resistance within the range specified in the value(s) column?
850-1350 ohms
Go to Step 6
Go to Step 8

6
Reconnect all connectors.
Carefully test drive vehicle above 24 Km/h (15 mph) for at least 30 seconds while monitoring a scan tool.
Does DTC reset as a current DTC?
--
Go to Step 9
Go to Diagnostic System Check - ABS

7
Replace wheel speed sensor. Refer to Wheel Hub/Speed Sensor Replacement in Front Suspension.

Is the repair complete?
--
Go to Step 10
--

8
If the resistance was low, check for short between CKTs 873 and 830. If the resistance is high, check for an open in CKTs 873 or 830. If repair of the jumper harness is needed, replace the jumper harness. Refer to Wiring Repairs in Wiring Systems.

Is the repair complete?
--
Go to Step 10
--

9
Replace EBTCM. Refer to Electronic Brake Control Module (EBCM) Replacement .

Is the replacement complete?
--
Go to Step 10
--

10
Carefully test drive vehicle above 24 Km/h (15 mph) while monitoring a scan tool for at least 30 seconds.

Does the DTC set as a current DTC?
--
Go to Step 2
Go to Diagnostic System Check - ABS

The same procedure applies for the other three wheel speed sensors. All that changes is the connector pin where you make the measurements.

Have you checked the EBCM ground G108 over by the battery? You should also check the voltage at the EBCM to see if it is at battery voltage.

Have you made any changes to the lighthing system? Changing the stop light bulbs might screw up the stop light switch signal that goes to the EBCM. This signal tells the EBCM that the brake pedal is applied.

To get the symptoms you are describing the EBCM has to think the car is still moving and one or more wheels are locked up. If one wheel speed sensor is indicating the car is moving then the EBCM will release the brakes on the other 3 wheels. Since you are getting speed variations on all 4 sensors it seems there must be a common source for the problem which may be a voltage or ground. A high resistance in the ground circuit may make the system more susceptible to radiated electrical noise that may be near you such as cell phones, etc. That may explain the randomness of the events.

Bill

 

Wow, Thank you Bill!

The process listed above does not sound like something I can do... is it suggested that the dealer preform this?

I have not changed any brake bulbs lately but will check them all tomorrow. I haven't made any other electrical changes, its stock.

The one thing electrical I can remember is on my last visit to the dealer I talked in detail with the tech and he told me (off the record) he would like to see the Alternator replaced as he thought the bearings were going bad and he felt the battery in the car was underpowered but told me neither of these caused the problem.

I had the alternator rebuilt over the winter, should I get a new battery this weekend just to rule that out?

I checked the grounds under the hood is there another I should check?

Great info, thanks

 

Check out Bill's sticky on the grounding locations and actions to clean in the tech section because there are other locations. It is easy to follow.

 

Holy hell!!!!!!! Man,,,did you get bent over DRY! That STEALERSHIP made some undeserved bucks out of your pocket! In the Navy, troubleshooting like that is called EASTER EGGING. Very expensive way to fix the issue, Just replace stuff till you run out of parts, cash or its fixed!

I really feel bad for you! The surging feeling that your expierencing comes from the EBTCM responding to various sensor signals telling the EBTCM that the brakes need to release to compensate for a wheel or wheels either loosing traction or sensing a signal that indicates the car is moving in the X or Y axis or YAW and laterial acceleration when it shouldn't.

Its a VERY serious and dangerous problem that need to be resolved ASAP! Thats NO BULL !!!!

If I were you,,,I would DISABLE the EBTCM and don't drive the car or only minimally drive it until we can figure out whats wrong.

First off, your getting DTCs for excessive wheel speed variation on ALL wheels. Thats telling me that you need to remove the MAIN connector EBTCM and read each of the wheel speed sensors from that connector. You should be able to read 850-1350 ohms on each wheel sensor.

Send me your e-mail address and I will attempt to send you a schematic that will give you all the pin out points to read.

Do you have any other electrical anomalies like your door not working or strange IPC/dash issues?

The only chassis grounds that effect the EBTCM are G104, G-101 and the ground stud on the EBTCM motor. They must be intact and working. Other than that, concentrate on the sensors in the circuit or the EBTCM its self.


There are TWO accelerometers that monitor the cars forward/rear motion and left to right motion. Lateral Acceleration and YAW One is under the radio and the other in under the carpet in the passengers foot well near the front of the inboard seat track ..

Theres a steering wheel position sensor that sends the EBTCM steering inputs that your making to steer the car in the intended direction that you want to go.

There is also a brake pressure sensor. Monitors pressure in the system.

The EBTCM collects ALL this data and tells the BPMV to apply or release the brakes. In your case, the EBTCM is sensing what it thinks is a skid or wheel lock up condition and is RELEASING your brakes to correct for it.

One or more of the sensors OR the EBTCM it self is causing this. We just have to figure out which one it is.

Bill

 

Thank you Bill! I have sent you my email address. I feel a little better as we maybe a step closer to getting this resolved but terrified that I have been driving with such a serious problem. It’s hard when she gets better mileage then my Trailblazer and winter has finally broke in Michigan.
I am not having any other electrical problems.
Please send the pics/diagrams and I will measure the speed sensors tonight.
The wiring harness that connects to the EBCM… how difficult/costly is it to replace that whole harness?
Thanks

 

I did not have the correct meter to measure the ohms but I disconnected the cable... It came off with very little effort, I have harder time opening DVD movie cases... I have a 1999 Auto, Vert, Canadian export.. not sure if that makes a difference but the connector on my EBCM/ABS module looks different. It did not have the white plastic clip or the grey handle and the second connector was a separate wire and not directly attached to the module.

(Mine does not look like this)


(Mine)





Like I stated it slid out very easy which concerns me that it may have been loose, after I got it out I could see the black tape wrapped around it from the last work done at the dealer ship. I flipped the connector over and found a slice in the yellow wire. I could see the copper. I separated it from the other wires and wrapped it in electrical tape. I inspected the rest but found no other problems. I placed it firmly back in the module and took it for a test drive. Over an hour I stopped the car and cycled the car over a dozen time without the error.

But this morning I got RFA codes U1096, U1064, U1016. Can the entire harness be replaced?

 

ttt

 

Another thing to remember is that some dealer repairs come with a lifetime warranty. Them may do future work in this problem for nothing. I would check you paperwork form the dealer to comfirm this.

T of T&C

 

Your car is a 99 right?

If so you have an early style EBTCM. Your connector will look like this:







If you have this style connector, you should have the latch that is shown in the picture and it should latch the connector in the module snuggly. Here is how the electronic module attaches to the BPMV.



So,,,you got rid of all the EBTCM issues????

BC