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Old 06-24-2020, 02:11 PM   #1
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abs question...

So the last time I started my 2001 Freightliner FS65 Thomas 70pax all hydraulic /electric bus the ABS light stayed on.

I still have good pressure feel on the brake pedal so I'm assuming (dangerous?) like on a similarly equipped car the brakes are still working fine but the ABS feature is NOT functioning -- off-line for whatever reason...

It's probably wiring from sitting in OH's damp weather but...

What is the procedure for reading the ABS trouble codes on a hydraulic equipped bus?

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Old 06-24-2020, 04:23 PM   #2
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Did you try resetting the ABS unit with a magnet?
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Old 06-24-2020, 04:47 PM   #3
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Try cleaning the pick up sensors at the wheels/axle.
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Old 06-24-2020, 05:20 PM   #4
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Quote:
Originally Posted by musigenesis View Post
Did you try resetting the ABS unit with a magnet?
I don't think my abs works like that -- it does not match the pix I've seen here of units where it does.

Quote:
Originally Posted by ol trunt View Post
Try cleaning the pick up sensors at the wheels/axle.
Jack
A likely source I agree. I confess, I've done nothing yet 'cause I'm not driving the bus enough to care yet.
Still, (with your example of the sensors) it would be nice to know WHICH sensor was acting up -- I don't like throwing darts in the dark till somthin' sticks to the wall...
If diagnostics can pinpoint the problem then I know whether what I do actually corrects the problem.

and I should have said in the first post -- the brake system is a BENDIX all four calipers are the same part (I really like that design!). The ABS (like a car) has an electric back up pump in the event of engine failure. Mechanical boost is hydroboost from the powersteering when the engines running.
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Old 06-24-2020, 05:52 PM   #5
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Perhaps it's just because I learned how to drive before all the technology took over but I don't care for most of it and that includes ABS. I have a pretty finely tuned butt-ometer and usually respond to the situation before the tech anyways. If it doesn't otherwise effect operation and you know how to drive the old fashioned way I'd say don't worry about it. Now of course I realize these days they have nanny systems for the nanny systems so it is possible that somewhere down the road something else will detect the continued ABS fault and flag some other CEL or performance derating or whatever.
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Old 06-24-2020, 06:11 PM   #6
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Quote:
Originally Posted by musigenesis View Post
Did you try resetting the ABS unit with a magnet?
Quote:
Originally Posted by Sehnsucht View Post
Perhaps it's just because I learned how to drive before all the technology took over but I don't care for most of it and that includes ABS. I have a pretty finely tuned butt-ometer and usually respond to the situation before the tech anyways. If it doesn't otherwise effect operation and you know how to drive the old fashioned way I'd say don't worry about it. Now of course I realize these days they have nanny systems for the nanny systems so it is possible that somewhere down the road something else will detect the continued ABS fault and flag some other CEL or performance derating or whatever.
He, he, he...
I too learned to drive looong before ABS was a thing... In fact I remember my dad taking me to an empty, icy mall parking lot one sunday afternoon to experience how the ol' '63 Impala wagon with a 427 big block liked to cut loose with a little go-peddle...

If you think your "butt-ometer" can analyse wheel speed / wheel lockup anywhere near as effectively as a proper abs system you are in a deep, deep mis-guided fantasy...

That said I'll agree that currently driving only a few miles in dry weather I don't need my abs working. I won't pretend to have any idea how my bus with worn tires handles in snow if I slam on the brakes...
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Old 06-24-2020, 07:22 PM   #7
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Well if you're gonna drive a bus in snow on bald tires then by all means get that ABS fixed!! LOL
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Old 06-24-2020, 09:43 PM   #8
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Well if you're gonna drive a bus in snow on bald tires then by all means get that ABS fixed!! LOL
How else will I learn what sliding that rear over-hang feels like?!
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Old 06-24-2020, 11:17 PM   #9
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my abs system

If you have bendix/bosch power steering pump assisted brake booster with an electric motor for back up emergency pressure... it is a Hydromax system.

I have a Hydroboost system with ABS... the systems are not interconnected. I have three wheel speed sensors, one at each front wheel and one at the rear differential. cleaning the tone rings and magnetic sensor for the fronts and removing and cleaning the differential speed sensor would be the second step or third step I would do.

1) check or replace fuses related to ABS

2) inspect wires to sensors and control unit for any damage, unplug connectors and inspect for corrosion

repair any deficiencies

3) clean pick up sensors and tone rings.

If you the abs light is on with out moving the bus, I think you problem is not related to speed sensors. If you have, and know how to use an oscilloscope you can tap into the speed sensors and watch the wave form. nice clean sinewaves are what you want to see, if the frequency is off by much or a dirty wave form then you will have problems. I would tap into right at the abs computer connections, that will also give you indications if the wires are okay too. I have seen one case of a gasoline engine ignition system feeding by way of inductance a speed sensor.....

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Old 06-25-2020, 04:52 PM   #10
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Quote:
Originally Posted by magnakansas View Post
If you have bendix/bosch power steering pump assisted brake booster with an electric motor for back up emergency pressure... it is a Hydromax system.

I have a Hydroboost system with ABS... the systems are not interconnected. I have three wheel speed sensors, one at each front wheel and one at the rear differential. cleaning the tone rings and magnetic sensor for the fronts and removing and cleaning the differential speed sensor would be the second step or third step I would do.

1) check or replace fuses related to ABS

2) inspect wires to sensors and control unit for any damage, unplug connectors and inspect for corrosion

repair any deficiencies

3) clean pick up sensors and tone rings.

If you the abs light is on with out moving the bus, I think you problem is not related to speed sensors. If you have, and know how to use an oscilloscope you can tap into the speed sensors and watch the wave form. nice clean sinewaves are what you want to see, if the frequency is off by much or a dirty wave form then you will have problems. I would tap into right at the abs computer connections, that will also give you indications if the wires are okay too. I have seen one case of a gasoline engine ignition system feeding by way of inductance a speed sensor.....

william
Thanks!
I'll search "hydromax and see if that's what my components look like.
I should make clear if my first post wasn't -- the abs light coming on is a recent thing. It came on with all the warning lights on startup sequence and would then go out with all the other warning lights.

But checking the fuses is sooo annoying what with the fuse panel not being labeled and having to find reading glasses... More seriously -- almost everything's on a circuit breaker but if I can identify the abs I can swap-shoot it for a known good one...

As said, all four of my calipers are identical and all 4 have their own speed sensor. Which with a quick look this afternoon I don't see how they come out of the caliper mount. No obvious fastener -- I don't like just pulling on things until I know they're a pressure fit like a roll pin for example...
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Old 06-25-2020, 07:56 PM   #11
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After a better look at the sensor going into the caliper mount I won't try removing it till I find proper instructions -- it may be that the wheels have to come off to access a fastener from the other side...

Anyway pix of the abs distribution block. No led lights on this model.

IMG_1872.jpg IMG_1874.jpg
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Old 06-26-2020, 02:04 AM   #12
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I am going to follow this thread 'cause the ABS on our bus will come on after 10 to 15 minutes of driving. I might learn something. The Freightliner dealer (waaaaaay back in 2016) said it was the tone ring adjustment and they did make it go away for a little while. It may need to be adjusted once again.


Does your light come on as soon as the engine is started, or does it have a delay of a few minutes?
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Old 06-26-2020, 07:22 AM   #13
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You probably already did this but there are some fuses for the system you will want to check and I know if you have a good scanner you can read the brake codes also.
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Old 06-26-2020, 10:18 AM   #14
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Quote:
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I am going to follow this thread 'cause the ABS on our bus will come on after 10 to 15 minutes of driving. I might learn something. The Freightliner dealer (waaaaaay back in 2016) said it was the tone ring adjustment and they did make it go away for a little while. It may need to be adjusted once again.


Does your light come on as soon as the engine is started, or does it have a delay of a few minutes?
With your air-brakes vs my hydro I don't know if our hubs would have the same tone ring. This is the first time I've seen a sensor install into the caliper mount rather than directly into the axle housing.

The light comes on and stays on -- no delay.
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Old 06-26-2020, 10:25 AM   #15
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You probably already did this but there are some fuses for the system you will want to check and I know if you have a good scanner you can read the brake codes also.
Yes, it's the knowledge of "what kind of scanner and how to" that I'm unfamiliar with on the bus.

My Saab for example uses a proprietary GM Tech2 scanner.
You can plug in a regular ODBII but it will only give very general and sometimes wrong information. The Tech2 will read in depth, allow you trigger the injectors independently and on and on...

my original question stands:
What is the procedure for reading the ABS trouble codes on a hydraulic brake equipped bus?
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Old 06-26-2020, 01:43 PM   #16
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Quote:
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Yes, it's the knowledge of "what kind of scanner and how to" that I'm unfamiliar with on the bus.

My Saab for example uses a proprietary GM Tech2 scanner.
You can plug in a regular ODBII but it will only give very general and sometimes wrong information. The Tech2 will read in depth, allow you trigger the injectors independently and on and on...

my original question stands:
What is the procedure for reading the ABS trouble codes on a hydraulic brake equipped bus?
Perhaps this Bendix Service Data Bulletin will help:


Bendix SD-13-4863.pdf


I scanned through it and it does have the proceedure for initiating a blink-code diagnostic. I do not know if you have the models indicated in the data sheet, but it may give you something to work with anyway.
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Old 06-26-2020, 01:59 PM   #17
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I borrowed a snap on scanner from a friend it’s limited but has useful info here is a picture from the brake section
Attached Images
File Type: jpg 9FD20E49-BA6D-4A97-887A-9CEEC67C0664.jpg (286.7 KB, 1 views)
File Type: jpg 89590C4E-D181-4F14-951C-CC7FBFC2A634.jpg (300.0 KB, 2 views)
File Type: jpg 364FC69B-8E30-4A63-AEFB-76DB833621A3.jpg (267.4 KB, 1 views)
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Old 06-26-2020, 10:30 PM   #18
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Bulb check

Your ABS light is supposed to light up when you turn the key to the “run” position. All those light are so you can confirm the lights work. The engineers call this portion of the start sequence “ the bulb check”. Idiot light don’t do much good if the bulb is not working. Notice I did not say burned out, but said ‘not working ‘.

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Old 06-26-2020, 11:59 PM   #19
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In the original post, Banman stated the ABS light comes on and stays on.
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Old 05-06-2021, 03:32 AM   #20
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Quote:
Originally Posted by banman View Post

my original question stands:
What is the procedure for reading the ABS trouble codes on a hydraulic brake equipped bus?
you have the same bus as me so it may be the same.

there's a switch (may be unlabeled ) right next to the J plug, round diagnostic port. once the bus is on you switch it and the abs light will blink a 2 digit code. (ex, 4 blinks pause, 3 blinks = 43 = rear passenger side axel)

also side note I recently learned if there is a ABS problem that is an actual problem, it may also trigger your check trans light.
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