Still trying to figure out what the devil's wrong with my brakes. I've bled and bled and bled, and no air. But pedal continues to go to floor. My ABS light is on, so I grounded the diagnostic connector per the FSM and I think I'm getting 5 lights. Th manual says to count the long blink + short blinks, but my light never goes out to start a long blink...It's just on solid, then 4 quick blinks. Then repeat. So if I count the on solid as the long blink, then that's 5. If I just count the number of times the light goes out, that's 4.

If it's 5, it's greater than 16 dump pulses in a short time.

If it's 4, it's RWAL switch closed.

The other odd thing, I cannot clear the code. The FSM says remove the battery for 5 seconds...I remove it for 5 minutes, and as I soon as I turn the ignition on, the same code is immediately back without even running the truck. I would think a code 5 requires the truck moving as it would be sensor related. So, if it's really a code 4, what does it mean the RWAL switch is closed? If I look at the ABS schematics, the only switch I see is called a RESET switch in the rear ABS valve itself. I haven't tested continuity on that switch yet (I will), but what exactly does that switch do or indicate?

Any help would be appreciated. I found a youtube video that says mushy pedal with/without vac assist and no air could be a bad ABS unit....So that's why I started looking there.

 

So here's the odd thing...

the connector to the RWAL unit is a four pin where the light blue wire and black wire are to the switch. The black wire is ground, the light blue wire is the ground signal back to the abs unit that says the switch is closed.

ohm the black and light blue wire at the RWAL and it's open. But ohm it at the connector going back to the engine bay and it's closed....wtf.

so in the engine bay it splits into two connectors...one is the ground signal and it checks. The light blue goes through a connector and then to the large firewall connector into the cab. The light blue wire is grounded...so the abs unit thinks the switch is always closed.

go into the cab and jiggle wires around trying to trace the light blue wire...I see it at the top of the abs unit but impossible to reach. For grins go back to the engine bay and check the light blue wire now and it's NOT grounded...aha I'm thinking...a skinned wire shorted in the cab.

to test I turn on the ignition and the abs light goes out like it's supposed to. But then it comes back on...wtf. I go back and check the light blue wire and it's shorted again....and I touched nothing but the key switch. So I'm wondering if the abs unit itself is bad causing this signal to show grounded. Maybe the wire moved again and re shorted but I swear I touched nothing.

 

Definitely the ABS controller is causing the light blue wire to ground. As a test, with the light blue wire tested with my meter to ground and the connector unplugged from the RWAL unit, it showed 0 ohms (at this point the light blue wire only goes to the ABS controller)...Keeping my meter on, I unscrewed the firewall connector which removes all signals and power to the ABS controller. Of course with it unscrewed, it showed open. Screwed firewall connector back in after waiting 30 seconds (removing power essentially to reset). Now light blue wired showed about 45Kohms (floating open to ABS internal circuitry). With meter still connected and RWAL still unplugged, turned on ignition to ON and the light blue wire immediately shows shorted to ground. And the code is the 4 blinks again, RWAL switch shorted even though the RWAL is still disconnected.

I guess I can try swapping the controller from my 95 to see if it clears up.

 

No ABS unit in my truck, so I haven't any experience I can share there. That said, and following your troubleshooting, I'm with you in suspecting the ABS controller is failing.

Your description of the code sounds like a code 4. The engine light comes on initially (the long blink), then starts blinking the error code(s) as I recall. But if the "4" repeats without the long blink in between, that would be a code "44". In your case 4 sounds more like it applies than does 44: battery temp sensor voltage.

 

These aren't engine codes...my ecm is long gone. These are specific ABS codes that the ABS controller blinks when you ground it's diagnostic plug. It blinks the ABS light.

 

I need to pay more attention. Any luck trying the '95 controller?

 

Haven't yet....it's impossible to get to without taking out the dash, and I really don't feel like doing that on two trucks right now. About broke my back changing out the vacuum booster....which didn't change a damn thing. I'm totally frustrated with these brakes.