How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Dave Nova Your Own Question
Dave Nova
Dave Nova, GMC Technician
Category: GM
Satisfied Customers: 19452
Experience:  ASE Master Certification. GM World Class Certification
Type Your GM Question Here...
Dave Nova is online now
A new question is answered every 9 seconds

GM sierra: I have a 2001 GMC Sierra. ABS brake light comes

This answer was rated:

I have a 2001 GMC Sierra. ABS brake light comes on intermittantly. When light is on ABS brakes do not work, if light is not on ABS brakes will operate properly. Regular brakes work all the time. Dealer seems to be confused. Said it could be brake modulator pump or computer. Dealer warns if brake pump is replaced and brake line brakes they will have to replace entire brake line by raising bed of truck off (dont even want to know that price). I've read about a bad ground causing similar problem. Any ideas on what is wrong?

Hello and thank you for trusting me with your question. My name is XXXXX XXXXX I will do my best to help you with your GMC problem.


Did the dealer check the ABS system for trouble codes? If so, what codes were in the system? If you are not sure, they may be noted on the receipt you got from the dealer. Codes would be a 'C' followed by a four digit number. For example: C0245.

Customer: replied 5 years ago.

I dont know the codes the dealer found and they still have the truck. At the time the dealer looked at the truck the abs light was off but they said the code indicated it was the ABS computer/module. The technician I talked to was not very confident that it was the computer/module. He gave me a nightmare scenario that said it could be the brake pump and if that was bad it sometimes takes the computer/module with it. And if they have to replace the pump he couldnt garauntee that a brake line wouldnt brake and if that happened they would have to replace the entire line.

If you can get the code information from the dealer, I can give you a better diagnosis of the problem. Yes, there have been some ground issues with these trucks and the first thing that should be done is to service the grounds at the drivers side frame. If that does not work and the codes come back then more extensive repairs will be necessary. We do sometimes get a code C0550 which would indicate a failure in the abs control module (EBCM). When this occurs, I have never seen the valve assembly be bad and replacing the EBCM has always fixed the problem. Any other codes in the system are usually caused by outside sources like the wheel speed sensors or breaks in the wiring. Sometimes we do see failures in the valve assmbly, but not too often. This is usually the most reliable part of the system. If the dealer will provide you with the code numbers and they are different than a C0550 let me know what you have and I will continue to provide you information on the possible failure.
Customer: replied 5 years ago.

okay, The dealer is closed now. Can I get you these codes tomorrow? How do I get in contact with you? Will this stay open even if I have to log off my computer?

You can get the codes to me tomorrow. The question remains active even if you log off. You will have an email with a link directly back to this quesiton. Use it for follow up, do not open a new question.


Customer: replied 5 years ago.
, ,

okay,  The dealer is closed now.  Can I get you these codes tomorrow?  How do I get in contact with you?  Will this stay open even if I have to log off my computer?

Customer: replied 5 years ago.



I called the dealer today. The code on the vehicle was C0265. They acted confident that it was the computer today but that was the case originally.


They didnt know about the GM Bulletin on the ground wire but they acted liked they checked everything and its the computer.


I'd really like to know your thoughts. dan

Thanks for the update. There is definitely a technical service bulletin about cleaning the grounds before attempting any other repairs when you have the C0265 code. The C0265 code is for the internal relay circuit in the EBCM (abs control module). I have included the bulletin below for you. If servicing the grounds does not help then you will be safe to replace the EBCM to fix the problem. Also if the module does need to be replaced, you can get one much cheaper with a better warranty than what the dealer will provide through Module Master.


Bulletin No.: 04-05-25-002E

Date: March 11, 2009

ABS Light On, DTCs C0265, C0201, U1041 Set and/or Loss of Communication with Brake Module (Reground EBCM Ground)


This bulletin is being revised to add step 2 to the procedure and update the Parts and Warranty Information. Please discard Corporate Bulletin Number 04-05-25-002D (Section 05 - Brakes).


Some customers may comment that the ABS light is on. Upon further inspection, DTCs C0265 and C0201 may be set in the brake module. It is also possible for DTC U1041 to set in other modules. There may also be a loss of communication with the brake module.


A poor connection at the EBCM ground is causing unnecessary replacement of brake modules.

The EBCM ground is different for each application. Refer to the list below for the proper ground reference:

^ Midsize Utilities = Ground 304

^ SSR = Ground 400

^ Fullsize Trucks and Utilities = Ground 110


Do not replace the brake module to correct this condition. Perform the following repair before further diagnosis of the EBCM.

Perform the following steps to improve the connection of the EBCM Ground:

1. Remove the EBCM Ground. The EBCM Ground is located on the frame beneath the driver's side door. If multiple grounds are found in this location, the EBCM ground can be identified as the heavy (12-gauge) wire.

2. If the original fastener has a welded on nut, remove the nut from the frame, and if required, enlarge the bolt hole to accommodate the new bolt and nut.

3. Clean the area, front and back, using a tool such as a *3M(TM) Scotch-Brite Roloc disc or equivalent.

4. Install the ground, then the washer and then the bolt to the frame.

It is important to use the bolts, washers and nuts specified in this bulletin. These parts have been identified due to their conductive finish.

5. Install a washer and nut to the back side of the frame.


Tighten the nut to 9 Nm (79 lb in).

6. Cover the front and back side of the repair area using Rubberized Undercoating.

An additional check can be made to ensure a good connection for the battery cable to frame ground. It is possible for this ground to cause similar symptoms with the ABS as described above.

Customer: replied 5 years ago.

Thanks Dave, Great information. I am pretty handy but not an auto technician. Is servicing the grounds something that can be done by a handy person or does it require special tools and a lift?


And it sounds like it is okay to drive the vehicle with a bad module but the antilock brakes will not work. is that true?

Servicing the grounds does not require a lift. You can lay on the ground under the edge of the truck to work on the grounds. Basically what the bulletin tells you to do is to remove the bolt, clean the ground terminal and the frame then reattach the bolt. If the bolt strips, drill out the hole and install a bolt with a nut on the back side and then use some spray undercoating to cover the bolt to prevent corrosion.


The truck can be driven safely with normal braking even with a bad module. You just will not have abs braking available when the light is on.

Dave Nova and 2 other GM Specialists are ready to help you
Customer: replied 5 years ago.


one last question. isn't it more likely for a ground wire to be intermittent than a module to work intermittantly? Dealer seems upset that I am questioning them about their diagnostics. They said they know about the GM Bulletin but I think they learned about it from me.

Both can cause intermittent problems. Electronic components and connections are susceptible to vibration, movement, moisture and temperature variances. Fixing the grounds is cheap and is a known problem. Like the bulletin says, attempt no other repairs until having serviced the ground connections. That is what I suggest to do.