95 k3500 abs

[94GMC2500]

Hello, I have a 95 K3500, I have abs codes 25, 26 and 37 but the ABS light isn't on. Also, I can't find a list of the ABS codes for OBD1. Can someone help me out with this? Tom

[DmaxMaverick]

25 and 26 are APP codes. Strange, as you shouldn't have both at the same time (#2 circuit HIGH and circuit LOW, respectively). 37 is TCC brake switch stuck ON. None of these should trigger the ABS lamp, but the STS (Service Throttle Soon) lamp should be on. It sounds like you have harness or connector issues under the dash. Maybe ground(s), which could be anywhere between the batteries and components. Look for rodent evidence.

[94GMC2500]

After lots of searching I found a list of OBD1 ABS codes, what I found is code 25 is L front speed sensor or circuit open. 26 is missing L front speed signal. 37 is erratic rear speed signal. these codes are supposedly for a 1995 chevy truck. Do these make sense DmaxMaverick? I got the codes by jumping the second from left lower terminal to the upper right terminal on the test port.

[DmaxMaverick]

The DTC's are revealed by jumpering the top row, right 2 terminals of the ALDL. I have no idea what would happen doing it the way you explained. Your list of codes doesn't match mine, at all. If ABS codes are revealed as you describe, I learned something today. I'm not saying it doesn't work that way. Only that during all this time, I've never had to visit this.

Is there an actual problem you are chasing? What are the symptoms? Do you have ABS issues? I'm intrigued.

[94GMC2500]

The brakes on my truck never seemed right, the brakes didn't have very good stopping power. Last year the brake to line to the left front wheel blew from rust and one chamber in the master cylinder went dry. I put on a new line and bled the front brakes by gravity bleed. the brakes seemed worse after that. I was wondering if there was air in the abs unit, so yesterday I made a plate with a rubber gasket and drilled and tapped it with a spark plug tap. I clamped it on the master cylinder with a C clamp and hooked up my leak down tester and put about 5 lbs of air on it. I then bleed all the brakes. took the truck on the road and the brakes were much better. In a panic stop from 30 mph it stopped fast and locked up the rear brakes. but when I locked up the brakes on grass it locks up the back wheels and the brake pedal goes way down, I dont know if that is from the abs kicking in or what. Anyway I was searching on how to bleed the abs but didn't find much but stumbled on to a video about how to get the abs codes.

[94GMC2500]

After slamming on the brakes 6 or 7 times on grass I could hear and feel the abs kick in. I pressure bled all 4 wheels again and the brakes are much better. I am not going to worry about the abs codes if it has good brakes. We are going camping in a couple weeks, hopefully it will stop much better now pulling our 29 ft camper.

[DmaxMaverick]

That's how I bleed them, but sometimes it takes more. 8-10 activations would be normal to get the air out. Sometimes more. I vacuum bleed from the calipers/slaves, then do several 30-0 activations on gravel. Grass would be OK, I think. Anything that allows uneven friction.

Your codes may be in history. If you lose wheel or speed (tranny output) sensor values, the ABS won't work, at all, and the ABS lamp should be on. There are so many reasons for weak brakes, the ABS is pretty low on the list. Other than having air, it has no effect on overall braking until there is a traction issue and ABS is activated. Maybe have a look at the mechanical side of it. Good discs/drums and pads/shoes are essential. Blowing a line changes all of it, and puts you back to square one. Drying up the master cylinder is another issue. If it was used that way for any amount of time, I'd likely just replace it. They don't like running dry, and plunger or bore erosion happens very quickly, especially if it's aluminum.