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Discussion Starter · #21 ·
So, I had a look at the fuses again and sometimes they aren't always easy to tell if broken. But, sure enough, the 40A ABS pump fuse under the hood was blown. I put a new one in and it popped almost as soon as I tested the ABS.

So it seems like the ABS pump is the issue. The actuators and valves work fine when I test them with my scan tool, they open and close no problem. My brake fluid is clean and there is no air in the system. Its the pump that is blowing the fuse when activated. I am wondering if I have a broken wire somewhere or if the pump itself is dead. Can I just get a scrap ABS module and take off the pump, I believe there are two screws securing it to the Hydraulic unit, and then swap it in for my broken one? It seems this would be a possible fix. Or, its an electrical issue, which sounds like fun....

I have always been a bit of a parts changer, I can do a lot, but diagnostics, especially electrical problems are not my cup of tea...
 

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Woober Goobers!
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PUMP/MOTOR
There are two pump assemblies in the HCU, one
for the primary hydraulic circuit and one for the secondary
hydraulic circuit. Both pumps are driven by a
common electric motor (Fig. 12). This DC-type motor
is integral to the HCU and is controlled by the CAB.
The pump/motor provides the extra amount of
brake fluid needed during antilock braking. Brake
fluid is released to the accumulators when the outlet
valve is opened during an antilock stop. The pump
mechanism consists of two opposing pistons operated
by an eccentric camshaft. In operation, one piston
draws fluid from the accumulators, and the opposing
piston pumps fluid to the master cylinder circuits.
When the antilock stop is complete, the pump/motor
drains the accumulators.
The CAB may turn on the pump/motor when an
antilock stop is detected. The pump/motor continues
to run during the antilock stop and is turned off after
the stop is complete. Under some conditions, the
pump/motor runs to drain the accumulators during
the next drive-off.
The pump/motor is not a serviceable item; if it
requires replacement, the HCU must be replaced.
 

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Woober Goobers!
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With the above description....I don't see why you can't replace the entire HCU. There's no programming involved. Find one from a wrecking yard. There are two HCU units. One with Traction control and one without. Make sure you get one that matches what's in your current vehicle.

Besides...removing the pump alone from the HCU may cause more problems.
 

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i don't think there is a relay in the under hood fuse block for abs.
might give the motor a few taps and try a fuse one step higher.
dead short will blow the fuse anyways before damage.

if you have power at the plug of the motor/module assembly,, key either on or off, whatever is necessary, then there is no short in the wiring, but a problem in the motor most likely.
assuming a good fuse when testing, or a light jumper.
at least you still have normal brakes while you figure it out.
 

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So, I had a look at the fuses again and sometimes they aren't always easy to tell if broken. But, sure enough, the 40A ABS pump fuse under the hood was blown...
From post no. 2: "...Doesn't sound like any fuse problems, but verify using ohmmeter rather than visual check (visual checks not reliable)."
 

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Discussion Starter · #26 ·
From post no. 2: "...Doesn't sound like any fuse problems, but verify using ohmmeter rather than visual check (visual checks not reliable)."
Noted lol

So I either replace the HCU entirely or there is a wire that shorted out somewhere. Not sure where to start looking for wiring issues, I have installed tons of stereo equipment, amplifiers and speakers in the 12V realm, but tracking down busted wiring or harnesses through electrical troubleshooting is something I detest. But, I think I need to do that step or have a mechanic do that step before changing the HCU.

The only thing is, that when the light came on, it was during a situation where the traction control was bring heavily engaged on snowy/slippery roads. I wonder if that heavy usage is what blew the motor?

I guess I will shelve this until the winter weather eases.
 

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i ride mine hard all over town when i leave to go somewhere.
all the hills and ice.
between trac control and abs, mine gets the occasional good work out every winter.
maybe that's why it's still working? :unsure:
like i said, the plug in at the unit will probably have power with a good fuse, and could be checked to rule out a short in the wires.
like all automotive, i'm sure it's pulse grounded to control motor cycling and power is on continuous.
probably controlled by key., or key and relay.
i used to have mitchell wiring diagrams when i ran windows, but it doesn't run on linux.
so grab the downloadable manuals from the site and look up the wiring to find it's path to test.
 

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Discussion Starter · #28 ·
With the above description....I don't see why you can't replace the entire HCU. There's no programming involved. Find one from a wrecking yard. There are two HCU units. One with Traction control and one without. Make sure you get one that matches what's in your current vehicle.

Besides...removing the pump alone from the HCU may cause more problems.
Removing the just the electrical pump motor? I know there are companies where you can send in ABS pump motor to be rewound. I don't see why this would cause problems.

I feel the HCU is fine, I really think its just the 12V DC motor that is caput.
 

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i think so too.
an internal short that blows the fuse when the hcu cycles the motor.
removal would need some diagrams i don't have to see exactly what's involved besides 2 screws.
that sounds a little too easy.
i don't know if the manuals on the braking system are that involved.
 

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Discussion Starter · #30 ·
i think so too.
an internal short that blows the fuse when the hcu cycles the motor.
removal would need some diagrams i don't have to see exactly what's involved besides 2 screws.
that sounds a little too easy.
i don't know if the manuals on the braking system are that involved.
No idea what car this is for, but the setup looks very similar to the LH cars. She makes it look pretty easy...

 

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i don't think your brake system is usable while the motor is out.
looks an easy enough task.
there are only a few braking systems that were used.
it's quite possible another manufacturer used the exact same system even.
made by manufacturers like bosch or somebody.

maybe that's why mine is working, is it was rarely used before me.
maybe i'll be a little more careful of it's use from here on.
 

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I had a 99 300m that had problems with the ABS. Everyone told me that the computer was bad. I looked at it myself and found that it was just a pin hole leak in the brake line that went to the rear brake. Once I replaced it it worked fine, As for bleeding the line I found that it would bleed itself by making hard turns and hitting the brakes.
 

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Discussion Starter · #33 ·
I had a 99 300m that had problems with the ABS. Everyone told me that the computer was bad. I looked at it myself and found that it was just a pin hole leak in the brake line that went to the rear brake. Once I replaced it it worked fine, As for bleeding the line I found that it would bleed itself by making hard turns and hitting the brakes.
The lines were all replaced with cupro in the last 3 years, the lines to the master cylinder were replaced a year ago and all the rubber hoses at the wheel were changed. I am also not losing any brake fluid.

Its for sure the pump motor. I have a replacement motor coming and will let people know how that goes vs changing the entire HCU...
 

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Discussion Starter · #34 ·
It's still winter here, a bit cold to be doing the work outside still. But I got a replacement ABS module and HCU.

The DC motor was super easy to remove and aside from making sure the silicone gasket seats properly when swapping out the broken one for this one, this seems like an easy process. What I like about it is I don't think I will have to remove all the brake lines. I should be able to wiggle it around enough to replace the motor in place.

Attached are some pics of the DC motor that I removed from the used part I got. Not too complicated.
Camera lens Cameras & optics Gas Camera accessory Electrical wiring

Automotive tire Bicycle part Rim Gas Bicycle drivetrain part

Drinkware Camera accessory Bicycle part Cameras & optics Gas
 

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cool
i'll have no trepidation to tackle it myself now if i ever have a problem.
i'm the type who likes to know what you're getting into before one starts.
in case of things like spring loaded flying parts you can't figure out where they belong. 🤣

winter here too in alberta yet.
we've been lucky and not too much cold this year.
christmas and early january saw a few -30+ nights.
lots pf freeze/thaw cycles since late january.

just about melts away, and it snows again.
after 26yrs, the belt finally went on my electric snowblower.
finally got a new belt and fortunatlly i haven't needed it since it broke.
maybe next year i'll get a cordless 80 volt to match my blower, trimmer, lawnmower.
 
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