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Old 04-22-2018, 07:03 PM   #1
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ABS light and switch under dash

Found this switch under the dash today and it makes the abs light come on when you press it. What is this for?Screenshot_20180422-180251_Photos.jpg20180422_165143.jpg
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Old 04-22-2018, 09:17 PM   #2
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It tests the abs system for proper operation.
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Old 04-22-2018, 10:39 PM   #3
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Quote:
Originally Posted by bluebird90 View Post
It tests the abs system for proper operation.
so you press the button and if the light comes on the system is working?

I thought you were supposed to press the brakes real hard when it's raining and see if you slide all over the place. JK
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Old 10-27-2018, 10:47 PM   #4
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Quote:
Originally Posted by aridgedell View Post
Found this switch under the dash today and it makes the abs light come on when you press it. What is this for?Attachment 21084Attachment 21085
What part of the dash is that button under? From what I understand that button can be used to get a code from the ABS system when the ABS light is on... and my ABS light is on...
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Old 10-28-2018, 11:37 AM   #5
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95% of ABS issues seem to be with speed sensors.. some of the earlier ABS were rear wheel only and only had 2 sensors.. one on a front wheel as a reference and one on the rear diff.. the better systems have speed sensors on both rear wheels or all 4 sets of wheels..



you may be able to call thomas and find out what ABS module you have (by VIN).. and then can begin looking up diagnostic info for it.. some of them have an actual diagnostic connector you can plug a scanner into, others you shorted a couple pins together on the connector and that would trigger a self test and the ABS light would flash out codes.. the trigger pins sometimes wired to a dash switch or to the starter-engage momentary circuit on the key switch. so the close and open of the starter switch would trigger the test on engine start.. without knowing which ABS computer you have its hard to tell... there were / are lots of them..

-Christopher
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Old 10-28-2018, 01:13 PM   #6
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The International buses I have been around the past 13 years have a row of lights on the module that will light up and help you pinpoint the problem. Will tell you front, rear, sensor, modulator, ecu. You can also buy a simple tester, Bendix #801869, that will plug into the diagnostic port and does the same thing, saves crawling under the bus and locating the control module. Typically what I find is bad connections where the wheel sensor plugs into the harness, if its showing a bad sensor on one corner I will unplug the connector and check the ohm reading on the sensor. If it shows around 1200 ohms then it should be good, then I wash out the connections with electrical contact cleaner, plug back in and reset the system. The control module and also the tester can be reset with a magnet so after you try a repair just touch a magnet to the end of the tester or on the module where it says "reset" on it and it will tell you whether you were successful or not. If the light stays out till you drive it over about 10 miles an hour then it comes back on then it could be a bad sensor, bad connection on the sensor, or I have seen the sensors back themselves out enough that they are too far from the tone ring and they cant get a reading. Hope this helps
Attached Images
File Type: jpg abs module.jpg (130.2 KB, 10 views)
File Type: gif abs tester.gif (11.5 KB, 53 views)
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Old 10-28-2018, 01:42 PM   #7
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great info!!
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Old 10-28-2018, 03:14 PM   #8
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I took my bus in for a government required inspection so I can get my plates for it and in the inspection the shop discovered that a piece of black tape was put over the ABS light so it couldn’t be seen. That would’ve been done by the school district. After searching yesterday I found ABS computer with the lights indicating the right rear sensor. Since I have to get the rear brakes and drums replaced (appt tomorrow) I’ll have them switch out the sensor. I’m working on the assumption the school district at least tried to fix this problem but stopped short to remove the rear wheels to change the sensor.

The maintenance records the school district gave me showed the front left ABS sensor was replaced in late 2016 and then readjusted early 2017 so I know they did do some ABS work themselves.

If I get a chance I might see if I can have a closer look. Does the wire just pull off the inside of the wheel or is there a trick to it?
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Old 10-29-2018, 09:21 AM   #9
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Here are a few pics of a sensor. The little gold piece is a clip that holds the sensor in place. There is a thick rubber grommet where the wire passes through the backing plate that you have to push out to get the connector to come through the backing plate. The connector on the sensor is the one that I typically have a bad connection problems with and try to clean them with electrical contact cleaner.
Attached Images
File Type: jpg abs 1.JPG (101.9 KB, 3 views)
File Type: jpg abs 2.JPG (74.8 KB, 3 views)
File Type: jpg abs 3.JPG (89.2 KB, 3 views)
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Old 10-29-2018, 09:28 AM   #10
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Thanks for the good info. I currently have an ABS light on my AmTran so I'm going to try what you said and see if I can get it to disappear.
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