ABS module bleed suggestions????

[lonfu]

1998 p30 chassis, 4 wheel disc with hydraulic brake boost from the power steering pump. Replaced the master cylinder with a bench bleed. Replaced the hydraulic booster. Replaced all 4 brake calipers. Checked the very short flex brake lines, no expansion obvious. Changed to dot 5.1 or super dot 4. Problem is a spongy brake pedal with no ABS light. I've vacuum bleed and power pedal bled the system several times with clean airless brake fluid coming out. Total of one gallon of fluid. I've tied down the brake pedal for a couple of hours to let air out of the lines to the ABS module. Original service manual says to bleed like regular brakes. No special method for bleeding the ABS module. My tech2 code reader, when I go through special functions, reads that it "can't connect to ABS module". No ABS light.

So, I assume that the ABS module is not tech2 compliant and it won't work. Yes, I have pumped the brake 4 times to bring the system to 35 psi, held and then tried to connect. Tech2 reader works for all other functions. Other sites have suggested that the tech2 will not work on the p30 chassis ABS brake module.

BUT I STILL HAVE SPONGY BRAKES, WHICH INDICATES AIR IN THE LINES...

I can only assume that there must be air trapped in the ABS module. How do I get it out? I don't see any obvious bleeder valves on the module. I do see a hex head bolt/cap that sits flush with the body that is inaccessible without removing the entire module.

It is a real head scratcher for me??? Anybody have any suggestions as to what direction to go here??

[rgatijnet1]

Did you change the short rubber brake line at the rear of your chassis at the same time you replaced the two front brake lines?

[77rollalong]

I have used the scanner tool to bleed the abs pump, not sure exactly what it does within the pump. but it does work, then you re bleed the system again after and you should get a hard pedal.
This is out of Mitchels on demand

1) raise and support Vechicle. Begin at the right rear wheel. Install clear plastic hose to bleed screw. immerse other end of hose in contaimer that is partially filled with clean brake fluid

2) Open bleed screw 1/2 to 1 full turn. Have assistant slowly depress brake pedal untill reaches full travel. Hold pedal untill bleed screw is closed. Release brake pedal and wait 10 -15 sec. repeat untill clean bubble free brake fluid is present at wheel bleed screw.

3) Check master cylinder every 4-6 strokes of brake pedal to avoid running dry. repeat procedure on left rear, then right front, then left front. after bleeding all 4 wheel go to the next step

4) Using scan tool in function test, run function test 4 times consecutivels while appling the brake pedal firmly. release brake pedal between each test.

5) Rebleed all 4 wheels to remove remaining air from brake system. ensure brake pedal feel is appropriat befor attempting to drive vehicle. Re bleed as nessary to obtain appropriate pedal feel.

[KJINTF]

Check you chassis wiring diagram
Not sure about your chassis

My 2008 W16 chassis has two Data connectors similar to most Mid to large trucks
The standard DTC 16 pin OBDII port where my Tech2 connects

PLUS

A 9 pin round J1939 connector where the ABS module and two CAN Buss are connected - The ABS module is NOT connected to the standard 16 pin DTC Connector in any way

I use the NEXIQ protocol converter along with WABCO Tool box software to access the ABS module - Yes the Tool Box software offers an ABS Bleed function. It works great