Did you check out the EBCM ground point under the drivers door at the frame? ABS Code C0265 Problem Diagnosis - Car Questions, Answers, and Discussion

Also, keep in mind that if it turns out to be a bad EBCM, they can be rebuilt. I had one rebuild by modulemaster.com. There are probably other options, too.

Gerald

 

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while the snapshot shows 9 pins, there are in fact 11. 2 are in the shadow.

 

have not attempted to correct the issue. still hoping the ABS computer will store a code other than C0265, which it lodged again today.

(for easy reference, the codes stored by the ABS computer over the life of the vehicle were B0237 B0265 B0245 B0251 B0252 B0241 B0242 B0246, or C0237 C0265 C0245 C0251 C0252 C0241 C0242 C0246, i intentionally erased those a day or two ago, when i bought the Actron CP9580. since that time, the only C0265 has been stored.)

from your rebuilder website

http://modulemaster.com./en/Chevy/Chevytruck_info.php

it looks like there are three different Kelsey Hayes modules on 99 silverados: 325, 310 and Series30. only the 325 is repairable, and the electronic module portion of the EHCM can be removed (potentially) without opening up the hydraulics.

based on the 3rd connector on my unit, depicted in the 4th and 5th snapshots above (connectors 1 and 2 are in snapshots 6 7 8 and 9), it looks like my EHCM is a 325 for which ModuleMaster would charge about $150 to repair. hopefully it will not come to that. hopefully the problem is simply an intermittent electrical ground.

i edited some of my initial posts to include some photos.

 

Really great pictures you posted! I hope it turns out to be something simple. On mine (Buick Lesabre), the EBCM repair for $150. fixed the problem and I have had no more lights since 2009.

One thing I did before getting the module repaired was verify that the modulator pump motor was OK. You can apply 12V to the two input pins (polarity does not matter) and hear it run.

Gerald

 

I have seen so many of these multi-code ebcm issues at work (GM dealership) that I can say it is a very common issue. especially up here in Ontario Canada where we still use road salt in the winter. The mosy commonly found issue is the multi-ground found on the frame/body mount on the drivers side by the body mount/frame. You will find a small 10mm bolt that has a ground junction with one larger diameter wire and I believe two smaller wires. remove the bolt clean the mating area really well and the eyelet of the ground wires. re-install and spray the bared metal with a rubberized undercoating or equivilant protector. I have found poor ground connections to be the main cause of many module issues. Try this and it might save you some money.

 

still holding off on correcting the issue. no codes yet today. Local library has a copy of Haynes Anti-lock Brake Systems ISBN 1563923491 While it is copyrighted 2000, it ends with 1998 models years. The book describes a dozen or two different ABS systems, including several Kelsey-Haynes systems, and includes a generic 13 page introduction chapter on ABS, but does not cover the Kelsey-Haynes 325 system.

Some guys over at blazerforum.com talk about DIY repairs on their KH 325 modules:

http://blazerforum.com/forum/2nd-gen...ey-hayes-55462

i added a couple more pics again to some of my earlier posts.

 

since buying the CP9580 from sears.com about 6 days ago for about $170, i've driven about 80 miles. On about 8 occasions, the ABS computer has stored the code C0265 and illuminated the ABS+brake lights on the dash, usually within 4-6 miles after having used the CP9580 to erase the codes. No other ABS or emission codes were stored during the 80 miles.

Based on the previous advice in this thread and others (Thanks!) i decided to first clean the ABS module's chassis-ground connection. While I've driven only 12 miles since cleaning it, the ABS+brake lights on the dash have not come and i'm optimistic that the C0265 code was due to an insufficient ground connection. I'll wait for another 100 miles to pass before declaring it solved. The general performance of braking system never seemed to suffer from this issue.

The snapshots below show what I presume is the chassis ground for the electronics of the ABS module, the EBCM. The ground connection is located about 2 feet forward of the actual ABS module, on the driver's side, under the door. Under the hood, first I disconnected the battery's negative terminal. Then under the truck, the 13mm bolt backed out 1/8" thick threaded frame (the treads can be seen in the second photo) rather easily. There was no nut on the backside of the frame. I used some 100 grit sandpaper to clean up the two mating surfaces (but not the outer side of the terminal, nor either side of the washer), then reassembled it dry while being careful not to strip the threads tapped into the frame . I then ran some errands covering about 12 miles.

If this has fixed the problem, I suppose I ought to disassemble it again, apply some grease to the mating surfaces, reassemble it, and add a washer and nut to the back side. If I had some rubber undercoating spray, i'd do that too, but i don't.

 

cleaning the ground did not solve the issue.

the ABS system is still triggering a C0265 and the ABS + brake lights on
the dash are still lighting up after a few miles of driving.

 

with the C0265 code, and the ABS + brake dash lights still coming up intermittently even after cleaning the 2 mating surfaces of the chassis ground located on the frame under the drivers door, i took it a step further.

I disassembled the ground again, cleaned the outer side of the eye-terminal, both sides of the washer, and the underside of the bolt head, as best i could, then tried to wipe clean the five surfaces with WD40 on a papertowel, then reassembled it and added a lockwasher and a home-depot metric nut to the back side, then squirted some WD40 over everything.

Also did some scan tool testing using the Actron CP9580. With the ground disconnected, scan tool was completely unable to link with the ABS module (but could link to the OBDII module). I was expecting the scan tool to show some codes, but even after reconnecting the ground, and with a successful scan tool link, no codes had been stored. This is pretty disconcerting, because a bad ground supposedly triggers a C0265. Yet here, a completely fail ground (disconnected) was not triggering any codes. Something is fishy.

I also jiggled the ground wire and the two wires leading to the pump connector. no codes were triggered. But disconnecting the pump connector did trigger a C0265 "Electronic Brake Control Module Motor Relay Circuit"




Under the hood, i tried to test for loose connections by jiggling the front drivers side Wheel Speed Sensor. No codes were triggered. Unplugging the sensor triggered a C0225 "Left Front Speed Sensor Circuit Open".

 

Removing the ground completely is probably not a test that will yield any helpful results. If it is the ground for a printed circuit board within the EBCM, it is likely that many functions would be affected. Unless I am mistaken, one of those functions is the actual storing and retrieval of the codes (kept within the EBCM itself).

I think I would try calling Modulemaster and see what they might have to say about the symptoms you have. You have nothing to lose and might learn something. It is even possible that they might be willing to test your module and, if it is good, send it back for just a testing fee...there are still some businesses that give good customer service.

Did you verify that your modulator pump works?

Gerald