I am new to this site and need some help. I am attempting to asist my husband in looking up some fixes for some codes that have come up. Our truck is a GMC 2002 2500hd 6.0. This truck has been wrecked and is in the process of a rebuild. The codes that are coming up are B0077, B2585, B2961, U1255, U1016. I have the definitions for these but need to know any fixes that anybody may have. Also I have two more definitions: low voltage on ignition 1 and malfunction of EBCM. Any information will be helpful.

 

Also does anybody know where the abs pump motor relay and ebcm relay is located on this truck?

 

Both of those are the same thing, they are located in the computer module (Electronic Brake Control Module) mounted to the ABS valvebody, located under the truck on the driver's side frame rail. They cannot be replaced individually, you need to get a whole new EBCM. Occasionally the ground point at the frame under the driver's door will go bad and cause those codes- remove the ground wires, clean the connections and reconnect.

For all the codes, since the truck has been wrecked, clear first and then see what happens. Low Voltage can be a stored code, otherwise you may have a bad ground wire somewhere or a bad battery/connection.

Since you are dealing with a salvage job I would highly recommend getting an ALLDATA subscription for that vehicle. You are going to be digging into a lot of stuff and will get diagnostic answers much faster that way.

 

We have used a snap on soltice diagnostic scan tool. after completing the scan it showed no codes but after running diagnostic tests the abs motor was showing off on the scan tool. He could turn it on, on the scan tool and the abs light would go off but as soon as he backed out of the program the motor went off and the light came on again. Any suggestions on this? All the grounds have been cleaned and properly reinstalled. Also this truck is not showing a "sis fuse". All other fuses are good.

 

If you use the scan tool to command the ABS pump to on, the pump will probably run at reduced output. What the EBCM is measuring is internal resistance across the pump motor circuit. The primary reason this fails is the relay goes bad and the contact has a poor connection, however it is permanently installed inside the EBCM block making it an expensive ($800) fix.

The reason the ABS light would turn off is the scan tool is taking manual control of the EBCM. When the scan tool releases control the ABS module performs its normal internal diagnostic and determines something is amiss.

 

Also when doing the diagnostic scan the rear abs sensors were showing within spec.. But the front two were not? It has brand new speed sensors in the wheel hubs that have been properly cleaned..

 

Again I would reiterate- your issues may be of complex nature and require expert technical advice. (I am not certified as Master Mechanic- I can guide but there is no guarantee what I know is correct) I would recommend getting a subscription to ALLDATA or Mitchell1 for service manual and diagnostics support.

The wheel speed sensors operate based on an AC voltage generated by the sensor itself. Measure output in the mV range with a quality high resolution multimeter or oscilloscope if you have one available. There may be a wiring issue on the WSS circuits that is causing your issue, again, that all traces back to the EBCM.