Z71-n-Z28
Full Member
My name is John. I haven't posted in years, but I figured I would chime in and write this in case it helps someone else out. I see tons of posts all over the place about people having issues with their GM EBCMs, despite replacement, regrounding, etc. etc. etc. I also found MANY posts where they just gave up and lived with the problem being unable to fix it. Here's my story about trying to resolve this. Before you read this, I will get right to the ending: the problem is not yet fixed on my truck (a 2005 Z71), but I now know WHAT the problem is. I just need to find out WHERE.
About two weeks ago, I had the classic ABS and BRAKE lights stuck on with a fast chime lasting about 10-15 seconds at startup. I tried reading ABS codes and no codes were present - at least at that time. After driving it, I found that I had codes U1000 and U1041 set. Both codes are related to class 2 communications between the EBCM and PCM.
Upon trying different things with my scan tool (Android based using Bluetooth called Car Gauge Pro), I found that I was unable to communicate with the EBCM at all. So, it would seem the codes are plausible!
I found a TSB about a bad frame ground and addressed this. The grounds looked perfect so I was not optimistic that this would solve my problem. It didn't. I started probing the EBCM connectors. I found two +12's and a ground. A test light confirmed I could draw current from these circuits - at least as much as the test light required. At this point, I consulted the service manual. The wires in the EBCM harness are on a number of different pages and are a bit hard to follow. Nonetheless, it seemed like I had everything covered (or so I thought). I checked continuity on the DLC line to the EBCMa and found all in order...
I went on the internet and found that the EBCM is fraught with internal solder connections. So, I pulled out my EBCM and opened it up. the solder connections looked pretty good, but not perfect. I went ahead and resoldered the connections to the EBCM connectors. I then put the EBCM cover back on using black RTV and let it sit overnight. You can learn how to do this yourself on Youtube.
I reinstalled it into the vehicle and it actually worked - lights went out! I figured I was done... No dice. After about 10 minutes the problem came back. The problem remained for a good week.
So, figuring there were still bad solder connections, I took the EBCM back out, unsoldered the solenoids inside and the main connectors so I could get at the other side of the board. OIn that side are a number of ICs. Everything looked OK, but I resoldered the ICs anyway. I then reassembled the EBCM.
Without reinstalling the cover, I connected the EBCM to the harness and started the vehicle. I didn't put the EBCM back onto the pump at this point. To my surprise the brake light went out, leaving me with only a ABS light. Hmmm that's a good sign I thought. I connected the scan tool and was able to establish communications with the EBCM! Of course it was throwing codes about not being able to drive the pump, etc.
At this point, I put the EBCM back onto the pump and connected everything. I left the screws out since I'd have to take the EBCM back off to replace the cover. I started the vehicle and no lights or chimes resulted. No current codes were being set. Upon taking the vehicle for a short drive, I found I had working ABS! Woohoo!
I then took off the EBCM and put the cover back on again. After letting the RTV cure overnight, I put the EBCM back on figuring all would be well. No dice.
I figured this problem had to be the EBCM - perhaps a bit of badness on the main board. I found a boneyard EBCM on eBay and ordered it up. I got the used EBCM and the attached pump. I took off the replacement EBCM and installed it onto the vehicle. It didn't work. Same problem.
Now the head scratching began. Could I have two bad EBCMs? A cooperative buddy loaned me the EBCM from his truck. That one didn't work either. Hmmm. What is going on?
At this point, I really needed a schematic for the EBCM harness that was all on one page and easy to read. So, using the factory manual, I sketched up a diagram using everything I could readily find. When I was done, I found two pins in the EBCM connector had wires in them and didn't appear on my schematic. Nor was it clear from my drawing how I was actually measuring +12V on the pins since my drawing only had the 60A circuit for the pump. Not believing GM found put the EBCM on the same monster 60A circuit, and knowing I hadn't accounted for two connections, I started looking through the vehicle schematics again. Turns out there's another power lead for the EBCM that comes from the BRAKE fuse (which I had checked suspecting it). It's a brown wire that comes from the I/P fuse panel.
This wire should have power. When I probed this pin, nothing, nada, zilch, 0 volts. Aha!!!! I kluged up a jumper to this pin and 12V. Eureka! The EBCM communicated! OK, so I finally know what the problem is, I just don't know why.
Staring at the schematics some more, I found that the BRAKE fuse exits the fuse block on the back of the panel. I took off the dashboard kick panel and probed this connector pin for +12. It was there.
This wire enters the main harness and goes through the firewall. There's another connector C101 that carries the brown wire down to the EBCM. It's right on the side of the underhood fuse block housing and very easy to get at. I opened this connector and measured a solid +12V. I also verified continuity between the fuse in the I/P and the connector. I checked continuity between the other side of C101 and the EBCM. Open circuit! Could it be a bad pin in C101 or the EBCM connector? They looked perfect but I used a piercing test lead probe and checked these. All are well.
So, at this point I know I have an open in the harness between C101 and the EBCM connector. The harness leaves C101 and runs down the side of the wheel well then under the car and goes along the left frame rail. That's where I am at this point. I really need to take off the splash guard in the wheel well to open up the harness where the C101 harness enters the main harness. It looks like the wires make a tight bend where this happens and seems to be the most likely place for the open. But, I'm all out of daylight... I've got this narrowed down to about 4-5 feet of harness.
I don't yet have an ending for this story, but I will post as soon as I figure this out.... I feel so close to a solution...
Cheers!
John
About two weeks ago, I had the classic ABS and BRAKE lights stuck on with a fast chime lasting about 10-15 seconds at startup. I tried reading ABS codes and no codes were present - at least at that time. After driving it, I found that I had codes U1000 and U1041 set. Both codes are related to class 2 communications between the EBCM and PCM.
Upon trying different things with my scan tool (Android based using Bluetooth called Car Gauge Pro), I found that I was unable to communicate with the EBCM at all. So, it would seem the codes are plausible!
I found a TSB about a bad frame ground and addressed this. The grounds looked perfect so I was not optimistic that this would solve my problem. It didn't. I started probing the EBCM connectors. I found two +12's and a ground. A test light confirmed I could draw current from these circuits - at least as much as the test light required. At this point, I consulted the service manual. The wires in the EBCM harness are on a number of different pages and are a bit hard to follow. Nonetheless, it seemed like I had everything covered (or so I thought). I checked continuity on the DLC line to the EBCMa and found all in order...
I went on the internet and found that the EBCM is fraught with internal solder connections. So, I pulled out my EBCM and opened it up. the solder connections looked pretty good, but not perfect. I went ahead and resoldered the connections to the EBCM connectors. I then put the EBCM cover back on using black RTV and let it sit overnight. You can learn how to do this yourself on Youtube.
I reinstalled it into the vehicle and it actually worked - lights went out! I figured I was done... No dice. After about 10 minutes the problem came back. The problem remained for a good week.
So, figuring there were still bad solder connections, I took the EBCM back out, unsoldered the solenoids inside and the main connectors so I could get at the other side of the board. OIn that side are a number of ICs. Everything looked OK, but I resoldered the ICs anyway. I then reassembled the EBCM.
Without reinstalling the cover, I connected the EBCM to the harness and started the vehicle. I didn't put the EBCM back onto the pump at this point. To my surprise the brake light went out, leaving me with only a ABS light. Hmmm that's a good sign I thought. I connected the scan tool and was able to establish communications with the EBCM! Of course it was throwing codes about not being able to drive the pump, etc.
At this point, I put the EBCM back onto the pump and connected everything. I left the screws out since I'd have to take the EBCM back off to replace the cover. I started the vehicle and no lights or chimes resulted. No current codes were being set. Upon taking the vehicle for a short drive, I found I had working ABS! Woohoo!
I then took off the EBCM and put the cover back on again. After letting the RTV cure overnight, I put the EBCM back on figuring all would be well. No dice.
I figured this problem had to be the EBCM - perhaps a bit of badness on the main board. I found a boneyard EBCM on eBay and ordered it up. I got the used EBCM and the attached pump. I took off the replacement EBCM and installed it onto the vehicle. It didn't work. Same problem.
Now the head scratching began. Could I have two bad EBCMs? A cooperative buddy loaned me the EBCM from his truck. That one didn't work either. Hmmm. What is going on?
At this point, I really needed a schematic for the EBCM harness that was all on one page and easy to read. So, using the factory manual, I sketched up a diagram using everything I could readily find. When I was done, I found two pins in the EBCM connector had wires in them and didn't appear on my schematic. Nor was it clear from my drawing how I was actually measuring +12V on the pins since my drawing only had the 60A circuit for the pump. Not believing GM found put the EBCM on the same monster 60A circuit, and knowing I hadn't accounted for two connections, I started looking through the vehicle schematics again. Turns out there's another power lead for the EBCM that comes from the BRAKE fuse (which I had checked suspecting it). It's a brown wire that comes from the I/P fuse panel.
This wire should have power. When I probed this pin, nothing, nada, zilch, 0 volts. Aha!!!! I kluged up a jumper to this pin and 12V. Eureka! The EBCM communicated! OK, so I finally know what the problem is, I just don't know why.
Staring at the schematics some more, I found that the BRAKE fuse exits the fuse block on the back of the panel. I took off the dashboard kick panel and probed this connector pin for +12. It was there.
This wire enters the main harness and goes through the firewall. There's another connector C101 that carries the brown wire down to the EBCM. It's right on the side of the underhood fuse block housing and very easy to get at. I opened this connector and measured a solid +12V. I also verified continuity between the fuse in the I/P and the connector. I checked continuity between the other side of C101 and the EBCM. Open circuit! Could it be a bad pin in C101 or the EBCM connector? They looked perfect but I used a piercing test lead probe and checked these. All are well.
So, at this point I know I have an open in the harness between C101 and the EBCM connector. The harness leaves C101 and runs down the side of the wheel well then under the car and goes along the left frame rail. That's where I am at this point. I really need to take off the splash guard in the wheel well to open up the harness where the C101 harness enters the main harness. It looks like the wires make a tight bend where this happens and seems to be the most likely place for the open. But, I'm all out of daylight... I've got this narrowed down to about 4-5 feet of harness.
I don't yet have an ending for this story, but I will post as soon as I figure this out.... I feel so close to a solution...
Cheers!
John
