• ABS light on
• Traction control light on
• Brake Warning light on
• Codes C1248 – C1255
• No communication with electronic brake control module (EBCM)
I always try to keep the diagnostic side as simple as possible: do the basics, get the codes, do the research and do it all as fast as possible.
This project starts like any other by establishing powers and grounds. All the fuses were good, and since communication with the rest of the car was perfect, the next best place to go is the EBCM connector to check for any connection problems or faulty wiring. Everything checks out prefect, so I’m leaning toward a faulty EBCM at this point.
Codes are useful, but bidirectional control and other functions of a good scanner can be even more helpful when diagnosing a condition like this. For this era of GM products, I use a Tech II for diagnosis. I like to run the “automated test” in the ABS list of options as per the diagnostic tree instructions. This allows a basic self-test of the EBCM functions. However, this particular car only showed that the “relay” was not on. Following the wiring diagrams showed the “relay” is actually internal to the EBCM. Another strike for a faulty EBCM.
This vehicle is equipped with several braking systems:
•Anti-lock brake system (ABS)
•Dynamic rear proportioning (DRP)
•Traction control system (TCS)
•Vehicle stability enhancement system (VSES) (w/JL4)
All of these systems work within the EBCM.
The brake pressure modulator valve (BPMV) contains the hydraulic valves and pump motor that are controlled by the EBCM. All the wheel speed sensors produce an AC signal as the wheels spin. The EBCM uses this signal to calculate the wheel speed.
The yaw sensor (w/JL4) is read by the EBCM as an indication of the yaw or tilt of the vehicle. The steering wheel position sensor (SWPS) is read by the EBCM to indicate the steering wheel rotation and position.
The EBCM performs an initialization test at the start of every ignition cycle, and this initialization sequence cycles each solenoid valve and pump motor for approximately 1.5 seconds. That’s why the warning lights stay on for 1.5 seconds after start up. The EBCM will set a code and the warning lights will remain on if it detects an error.
On to the Repair
With the wiring checked, the codes verified, and the lack of communication, it’s safe to assume the culprit is the EBCM itself.
After replacing the EBCM, you’re not done yet — it needs programmed. Even after replacing the EBCM, the warning lights will be on, and there will be codes stored as well. In this case, the codes that stored were the exact same two codes I had before (which is a little disturbing), except the C1255 code had some extra digits added — C1255m3. The “m3” indicates that it’s not a programmed EBCM.
On to Programming
This is where my diagnostic information left me hanging (at least with the system I use). In fact, the only information given for this situation was: “Perform the setup procedure for the EBCM” – “Refer to the Techline Terminal/Equipment User’s Instructions.”
I spent a great deal of time going through page after page of misleading information until I found the correct procedures.
If you’re using a Tech II, you should also be familiar with the TIS 2000 program. You’ll need both in order to perform the programming. If you’ve reconfigured a BCM with a Tech II, you know there is a heading for the BCM, but the EBCM is not there. This program is located in the TIS program only. In addition, the transfer to the Tech II is not as straight forward as reprogramming a PCM. This time around you have to bring the laptop to the car and hook the Tech II up as a pass through device. It can only be done by way of the “pass through” section of the TIS program.
Once you have located the appropriate software by following the guidelines outlined in the TIS program, it only takes one click to start the download, and the download should only take a few seconds. When it says “complete,” you’ll notice the warning lights on the dash have all gone out. Cycle the key on/off, and disconnect the scanner.
At this point, all the codes should have erased from the memory providing there are no additional problems with any other part of the ABS or traction control system.
These days, the information you have will often lack one or two vital steps that are needed in order to complete the job. Then you spend even more frustrating hours trying to figure out how to accomplish that missing step. In this case, I spent hours trying to find the proper route to get this program installed. Hopefully after reading this you won’t have the same problem as I did.