I think you're mistaken. The FSM diagrams above are clear that they are in separate places (fluid level switch is in the reservoir, PDWS is in the Combination Block).

Can you cite where in the manual the fluid level sensor is part of the Pressure Differential Warning Switch? If it's stated that way, it's another mistake in the FSM, certainly.

 

I see it happen with AWD's when the master cylinder gets low, it triggers both the ABS and the brake light cause my 1997 is AWD and it happen to me.

I just mentioned it in my last post. If you look at the different setups you see all they changed was they removed the PDS "big word for normally open contact" they used the resevior monitoring now, cause it does the same thing. You lose fluid in any parts of it triggers a problem, the combo valve would see the same and close off the rear brake lines so they removed it.

 

I might add if you get moisture/trash in your brake lines and it sets for a long time, it can keep any of the many distribution valves or blocks from working properly. One reason I bleed the whole system every two years.

 

Yes, low fluid level will cause both the RED brake light and RABS code 12 on our '97s without PDWS.

Even when there was a PDWS installed in a RABS system, it did both of those. That's clear from this diagram:



But that doesn't imply that the PDWS is the same as the fluid level sensor. The PDWS has been deleted on our '97s.

The level sensor does not sense pressure differential on the spool valve in the Combination Valve.

 

Its all tied to the ABS loopback module under the dash. If you look on the driver side fender well under the brake booster you see where they use that pressure distribution block and electrical system. The signal from the resevior sensor sends all imput back to the module. It triggers a fault even if its just low brake fluid, it does not matter if its full, it just knows there is a problem and closed the rear off. One reason you get spongy brakes when the ABS light on. You can bleed the system with 5 gallons of new brake fluid. You will still have spongy brakes till you fix it . And unplugging the system will not. You have to fix the problem to get firm brake pedal back.

think of it like this, low brake fluid is a PD in the system and the system does not need extra sensor's to know that low brake fluid causes that.


the light and unplugging wii

 

I don't have a constantly-ON Red brake light, and I do not have spongy brakes, in any case the brakes are great, very smooth, and no pad noise, no rotor warpage.

still haven't found an ohmeter, mine has a bad/loose rotary switch, makes it unpredictable.

 

I'd guess that you don't have a failed fluid level switch, either.

I just re-read this thread, and I don't see where you've cleared the code 12 from the RABS module. Have you?

You might have been low on brake fluid, did a single hard stop that triggered the RABS, and the fluid sloshed enough to close the fluid level switch for one second. IOW, it might be a spurious code.

If you reset the code, I'd avoid using the parking brake for a couple of days. If the RABS light stays off that long, then resume parking brake use.

You didn't replace your brake lamps with LED ones, did you?

 

Al,
I did erase the KAM after getting Code 12, (well I THINK I did, by disconnecting the negative battery cable for half hour while I assembled everything back), and also after replacing the diode and resistor (the old ones turned out to be good), no change.

I use no LEDs anywhere, I have no burned-out stop lights, all lights perfect, **when I bought the van in May, the RABS light was on, so I don't know the history. Recently I went to a salvage yard, pulled and installed two other (used) RABS Modules from other 1997 Aerostars, (with the correct part number for RABS II), no change. All 3 modules appear to be good. Does not appear to be an issue with the module.

the RABS Amber light goes through SELF CHECK normally during startup, then comes back on and stays on. The RED Brake Warning light does not go through SELF-CHECK, but it works fine with the emergency brake lever/handle. This is one issue I do not understand because in my 1992 shorty, the RED brake light did not go through self-check either, so it came as as surprise when I learned it was supposed to.

I went through ALL the FSM troubleshooting steps until I got to REPLACE IGNITION SWITCH. But the ignition switch and steering lock work fine, I just can't see how it can be bad.

if I start the engine keeping the brake pedal PRESSED, the RABS light stays off until I release the brake pedal. Obviously something IS working! Two days ago the light did not come on after self-check, it actually stayed OFF while I drove, incredible! I thought the bulb had burned-out, but then it came back ON. *#%!(@# !!! I went to Walmart tonight, and it stayed on.

the brakes feel fine, a lot better than my 1992 shorty which had a harder pedal.

I have spent time looking very carefully underneath the van with a very bright lamp, at all 4 corners, looking for any signs of brake fluid leaking, nothing, nada, totally dry, I did find one wishbone bushing is almost gone.

One time I removed the RABS FUSE thinking it would clear any old codes, and also replaced it with another just for renewing it; the light went off and stayed off for a week, then came back on. Again, something in the system MUST be working in the sense that the RABS light persists in coming on and staying on.

 

I've packed up both my computer and my manuals, so I can't go looking, but for a different code (I think) there is a reference to a "Reset Switch", which during reading I thought might be internal to the RABS block. That's the only thing that comes to mind WRT the RABS light staying off until you release the brake pedal at startup.

One of the notes for code 12 says that a short in the STOP lamp will cause code 12, but I can't figure out what that means, looking at the diagrams. At first, I assumed that they meant the RED brake warning light, but I saw it twice, and now I'm not so sure.

In any event, I am without the usual resources for at least a month -- I'm traveling -- I can't make any good guesses or pretty pictures for a while.

I mentioned the LED brake lights because they are known to cause problems with the transmission, unless you add a resistor in parallel with them to get the current draw back up to near OEM. Since that same circuit feeds the Cruise Control, the transmission control, the lamps, and RABS, I thought it might be related.

 

The brake light circuitry also affects the E4WD computer.

 

too much for my confused brain. I just want the darned light to go off!

 

I received the new Reservoir today but it has a double connector underneath, one side for the fluid level switch and the opposite side for the proportioning valve sensor which mine does not have.

well at least I can see where the float is located and how it operates up and down, it's behind the rear wall, it's not a ball float but a "rounded-on-two-sides" rectangular piece. Now I can check if mine is stuck. I was checking in the wrong place.

 

I figured you missed it, when you said you didnt have one or they replaced it with the wrong one before you got the van. Just look at the system parts as is normally open or closed and how can I test it. you will understand how that engineer made it crazy hard.

 

the real crazy thing is that I cannot find the float in the old reservoir, it must be really stuck at the bottom. I've tried everything including a pick tool to try and raise it, but no cigar. the other crazy thing is that the switch connector is removable in the new one, very easily removable.

 

I uploaded part 3 showing what I got, how.to rebuild it and what to look for when picking one.

http://youtu.be/H3N1yLwPeYA


If you want to see the finished product let me know and I will post a part4 after I paint it.