Skip to main content
Topic: ABS Troubleshooting (Read 7984 times) previous topic - next topic

ABS Troubleshooting

I upgraded to Bear Claws and (with a little machining)  was able to retain the ABS.  Until recently it was working great but now my right rear locks up on hard braking with an ABS light.  Does anybody know how to troubleshoot the system?  So far my searches haven't borne any fruit.  I'm thinking wheel sensor but I thought there was a procedure.  Any help would be great.

ABS Troubleshooting

Reply #1
yes there is a diagnostic connector to pull codes but do this......


compare the toothed ring orientation to the brake sensor on the defective wheel to the left rear (compare condition)

also, with the control module is turned off, your brakes work as normal power brakes.

since its happening to one wheel, inspect the pads as well as the magnetic sensor parts back there. 

not sure what state your in, thinking debris may have built up causing the sensor to not act right.


I havent done a write up on ABS T/S yet, doesnt really look all that bad though.

ABS Troubleshooting

Reply #2
sorry, totally forgot to do this,, been a hard couple weeks at the cassity's.

im away all week, this weekend ill dig something up.

ABS Troubleshooting

Reply #3
No worries, I thought there was a connector under the deck lid that would flash codes but I couldn't find one.  Surprised so few threads on the subject.


ABS Troubleshooting

Reply #5
Excellent article but doesn't delve into the ABS aspect of the system.  I'll check the spare tire area for that connector.  I assume you can jumper it and it will flash the ABS light.  Hope codes are in my shop manual.

ABS Troubleshooting

Reply #6
Found two ABS connectors near the spare tire that exit the bottom of the trunk.  Are these the ones used to diagnose faults?  I was expecting an OBD type connector.

ABS Troubleshooting

Reply #7
Although you have an ABS light, I suspect that your trouble is purely mechanical.

Shiny Side Up!
Bill
"as if 'religion' were something God invented, and not His statement to us of certain quite unalterable facts about His own nature." -C.S. Lewis

ABS Troubleshooting

Reply #8
The diagnostic connector is up next to the ABS computer behind the rear seat. It looks like the engine diagnostic connector.

Page 12-29 of the shop manual begins the trobleshooting according to the EVTM. I'd be looking for a mechanical issue first. I always start with the last thing I messed with.

ABS Troubleshooting

Reply #9
87 shop manual
Chassis Electrical Part 1 of 2, Vol B

Page 12-32-1 starts the "Tbird" Anti Lock brake system consisting of 110 pages of component level troubleshooting.
Page 12-32-21 shows the diagnostic connector and is located near the ABS module as already stated.

At this time, this is what I have found.

-Codes are pulled by way of a Star tester or a break out box.
-I have not found a way to pull the codes directly from the diagnostic connector and I do not believe there is a known way at this time.
-I have not found yet the wiring diagram for the break out box
-No two codes with the same starting "Tens" digit can be stored at the same time. 
---ie- code 21 and 24 can not be stored at the same time but codes 2x and 3x can be stored.
-ABS can only store up to 7 codes at a given time.  Fix one code the re-test to find more codes that are able to present themselves.
-Once all codes have outputted and been serviced, the codes can only be erased by driving the car above 25mph.

In order to figure out what diagnostic procedure to follow, it is probably best to compare the shop manual ABS warning lamp sequence of illumination as a guide to further pinpoint the next specific related troubleshooting step. 
IE- the time frames or frequency of the "Check Anti-Lock Brakes" and "Brake" warning lights.

In various instances the "check abs" and "brake" warning lamps will illuminate but at certain times one lamp could be on while another is off.
The shop manual does a good job of comparing the two lamps with respect to several operational aspects of the car and its situation such as cranking, starting, at idle, while braking ect.

I will post this chart(s) up as well as a few other related pages to help on this aspect of our cars that has been neglected.
Using the lamp illumination chart and comparing what lamp is on when, points to a specific troubleshooting step further in the the collective 110 pages dedicated to this subsystem component level troubleshooting.
Since we do not know how to pull codes from the diagnostic connector like we do on the EEC, the only realistic and documented path is by way of using the warning lamp sequence chart.

I have found the wiring diagram illustrating the harness from the ABS module out to all its sub components useful.  It helps point to sensors which are called out with associated documentation calling out resistivity ranges and / or voltages to expect when a test is performed.

What i would like to know is more information on the breakout box and if it simply intercepts the ABS harness wire for wire, pin for pin.  This seems to be a reasonable application to a typical break out box since the ones Ive used did just that.  It gives you a way to tap into the active harness while not poking at wiring. 
If the above is true, then we really do not need a break out box at all, as we all can poke at the wiring by using stick pins and get the same information.

Hope this is helpful so far

I will post and link the ABS scanned pages to the EVTM link soon, hopefully this weekend.

ABS Troubleshooting

Reply #10
In reply to jcassity

Sounds like you are off to a good start. I recall a guy on NATO mantioning he had 'all' the Ford tools. I wonder if that included the ABS breakout box. If you could borrow one for a while you might get a little more insight.

Nice work!

ABS Troubleshooting

Reply #11
ok
putting this dog to rest although the original poster may be long gone which is unfortunate.

I completely understand the ABS system at this time.
Now to link in some documentation.

To follow up on a couple open items.

-The break out box transitions a 50 pin connector to an ABS adapter gender changer to 36 pins.
--the shop manual refers to pin numbers that exceed 36 when troubleshooting and i concluded that within the gender changer some pins are bonded together or not required.  Not a logical move in my opinion as referring to a "pin40" on the break out box has no association to the evtm or the shop manual illustration of the ABS module connector.  It is however logical as there are only 36 pins on the ABS connector. 

-There are only 25 used conductors at the ABS module but the number sequence follows the correct count as to which position on the connector the wire occupies.

-**** in my EVTM link below, Page 122 on the RH Rear brake sensor, Ford forgot to label the PK/BK conductor to which pin it goes to.  The pin number is ABS module pin #6.

-It appears that if one were to follow the shop manual without using a breakout box, he/she could simply follow all instructions as though there were a break out box, just as i had suspected.  This is only true about 95% of the time for reasons that are too in depth for now, but the good news is that most all troubleshooting steps are easy to follow.

-Pin 40 or pin 9 are referred to in the manual but at this time i only feel comfortable in saying the referred pin40 is either chassis or internal reference ground.  I am not sure what they are doing in a couple steps calling out pin 9 and bonding it to pin 40.  perhaps to manually activate the main power relay?, not sure cause it looks like thats an instantanious blown fuse situation.


so...lets troubleshoot!

ABS Troubleshooting

Reply #12
Ok,
Another 3 hours and i have updated the physical EVTM drawings with useful information to be used while troubleshooting.
Please note that the comment on the wheel sensor voltage ***IS*** in AC volts for a reason and is not a typo.

Just update your records with page 122,123, and 124 as the only changes.

To the original poster-
Having your rear wheel lock up makes no sense even using the shop manual.
The rear ABS (both wheels) are on common Inlet and Outlet hyd solenoids.  The fluid path is a single line up until it branches off to each right and left rear wheel.

I would conclude that there is probably two faults...
- your rear right wheel sensor is either too close or too far away or simply not installed correctly and the rear left caliper is in a bind.
you should be experiencing both rear wheels locking up but you are not.  I suspect the equipment you installed is done incorrectly or out of wack somehow.

There are no symptoms in the shop manual that bring in a diagnostic step to cure only one rear wheel locking up.  I would say to check and see if the other rear wheel caliper actually works and if not, bleed the line for it must have air.

like i said, they both should be doing the same thing and if thats the case, a normal probable fault would point to the Inlet rear and outlet rear solenoids.

ABS Troubleshooting

Reply #13
Update again, over some coffee since i slept in.

I should have started my research using the "1987 Shop Manual Supplement" which basically answers all my previous questions.

-Pin 40 as refered to in the shop manual is considered as Pin1 chassis ground.
-Pin 11 as refered to in the shop manual is considered as Ref gnd to the valve body ground.
-Pin 11 as refered to in the EVTM appears to be bonded to the wrong location on the valve body.
-All valve body solenoids termination points at ABS controller conflict the EVTM and Shop Manual., however the cirucit ID does match.  One could conclude that locating the correct ref gnd will allow a better starting point.

ABS Troubleshooting

Reply #14
Update again,
please replace your current page 124 of the evtm with the latest revision.

Revision includes steps to actuate valve body solenoids to determine thier operation is good.