Abs Haunted

Motohead

SCCoA Member
Ok Ive ben fighting this for about 2 years now. I have poasted on this subject before but no one could figure it out, here goes.
Right after I got the car the ignition switch went out. I replaced it with an autozone special. After I was done I noticed the breaks got hard after driving it around a wile. I also found if I turn the ignition switch past run and hold it before the starter engages the ABS pump moter would run, charge the break articulator and cycle. 2 to 3 pumps on the pedal wouild cycle the pump for about 3 sec (Act normal) with the key in the normal position after 15 pumps or so I get no breaks. I have replaced the relay and the ignition switch with a dealer part . NEW INFO today as I was sitting in my driveway I turned the key to on and herd the pump run. Thats different I thought has it fixed it self???? nata turnes out with the emergency break on (Lights the break light on the dash) the system functions properlly I tested this by driving the car with the emergency break pulled to the first click the break light stays on but the ABS pump cycles normally. Now the only thing I can think of is the system is not geting power and somehow it backfeads through the dash light when I pull the emergency break rember this all seemed to start after replacing the ignition switch and I had ford triple check the part number they say its the same part for SCs and non SCs which to me dosent make any sense as non SCs dont have the pump. Any help would be appreicated!!
 
Extremely doubtful on the electrical backfeed scenerio. I will check again tonight when I have the EVTM in front of me. The ABS Pump motor draws too much juice for a backfeed through this essentially unrelated electrical circuit. I would suspect instead a bad AntiI Lock Pressure Switch has been the majority of this problem for you all this time.
 
It is basically under the unit between the pump motor and the rest of the ABS Hydaulic Actuator Unit. It screws into the body of the unit from the driver's side. Requires a special thin line socket for removal. Has a 5 pin connector (if memory serves) plugged into the end of the pressure switch. Reportedly better accessed from under the car and I suggest unless you are good to have it replaced at the dealer. If this is not the source of your problem you may be looking at a reman of the system since at that point it is probably the motor that is going bad for the pump. It has a themal overload feature that prevents the motor from overheating.

The only other suggestion I can make is be sure the brake reservior is full since the level switch also shuts off the motor to protect it from being run dry. Usually though you will get a flashing red light (Brake Light) on acceleration and deacceleration of this is the cause...a symptom you have not reported.
 
I’m thinking about your last post. Dose that pressure switch do anything besides energizes the pump relay after the system pressure drops. With my break handle pulled the pump cycles with 2 to 3 presses on the pedal and the pump runs for about 2 seconds then shuts off. This tells me that the pressure switch is good as the system cycles.
 
Motohead said:
I’m thinking about your last post. Dose that pressure switch do anything besides energizes the pump relay after the system pressure drops. With my break handle pulled the pump cycles with 2 to 3 presses on the pedal and the pump runs for about 2 seconds then shuts off. This tells me that the pressure switch is good as the system cycles.
The pressure switch is actually 3 switches activated at 2 pressure levels. One switch controls only the pump motor relay and thats it. The second sends a signal to the ABS computer. The 3rd lites the "brake light" bulb whenever system pressure is below where its supposed to be.
 
To add to the last (since I am now home and can check) you basically have a branch circuit for the Brake Light. If the Anti-Lock Pressure switch activates it provides a path to ground and completes the circuit causing the light to come on. Off of a splice there is an alternate path to ground that as long as the Brake Fluid Level Switch is not sensing a low level...the path essentially bypasses the Level Switch and goes to the Park Brake Switch. If level IS low that switch provides the ground required to get the light to lite. If the Parking Brake switch is closed (parking brakes applied) then you get the light. Point being that in each case a ground is being applied to the circuit so there is essentially no "power" to be feed back into other parallel circuits. Thus my reasoning that what you observed is just coincidence. The Pressure Switch decided to work when you messed with the Parking Brake Handle.
 
So I should replace the pressure switch ?
What book do you have and where do I get one ?
 
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That would be my suggestion based on the symptoms you are relating.

I get my info from the Ford Shop Manuals as well as the Electrical and Vac. Troubleshooting Manual (EVTM) as well as the electrical schematics in some cases. All can be bought via ebay on ocassion at least and depending on what year SC you have can be bought from Helm Inc. who publishes the books and such for Ford.

(Moderator Edit: Link is: www.helminc.com)
 
Well i'm off to the parts store for the pressure switch and I called Helm and ordered the EVTM and shop manual (Thats all they have in stock) thanks for your help!! I'll post after I replace the switch. 1 question, I assume I should pump the breaks to drop the sustem pressure before I remove the switch; but will I loose fluid and need to blead the system afterwards? Thanks in advance!!
 
My ABS failing also

My ABS and brake lights are staying on, can barely stop car. Problem is intermittent. If you find out what wrong with yours please email me and let me know. Ford is asking for $3560 in parts plus labor to try to fix it. Will sell car before paying that price.

lac6@pge.com
 
Well...most likely we can help you Lee figure out the problem. First thing to try is replace the ABS Pump Relay on the passenger side firewall in the engine bay. This is (if an original part) a brown based relay mounted into a tray just below the plastic cowl next to the BAP sensor. I assume you have a 89 to 92 SC right?
 
It's a 1990, all original, 240,000 miles! (bought it new) I have to "nurse" it home from the Ford Dealer tonight after getting their diagnosis and not wanting them to touch it. I'll look for those parts when I get it home.
 
The absolete worse case would be a Prior Reman unit which is only 400 bucks or so plus the R & R so don't get too upset yet.

The reason you have no power brakes is the hydraulic pump is not running. That can be because of 1 or more of 4 causes listed in order of cost to repair. (These are the most common things I have seen.

1) Blown fuse (check them all now before you dive in.
2) Bad relay (about 15 bucks at Advance or AutoZone. Sorenson SP120 is the part number if memory serves.
3) Bad Pressure switch. Ford cost under 200 bucks installed.
4) Bad pump motor (looking at remanned unit 400 bucks)
 
I'm reserecting this thread because I have just got the car running (Blown motor) and I still have the same symptoms as before. The pump runs and cycles normally if I hold the key at a point after "on" but before "start" (the AC and radio quit with the key in that position).....The system also acts normal if I set the parking break to the first click just enough to turn on the brake light. By normal I mean after sitting overnight the pump runs about 30 sec (charges the actuator) then stops, when I pump the breaks I get a 1.5 sec pump run after each 2nd or 3rd break pedal pump. I think this proves the relay, motor and pressure switch are all good. Which only leaves wireing. is my logic correct ?
 
Well..sounds like your ignition switch is bad IMHO. If things work sometimes and then don't work at others and given you can get the to run normally by messing with the key seems pretty logical to me.
 
Which part did you replace?

There are two components for the ignition switch. One is the actual switch mechanism (the rectangular box with the wiring harness connection), and the other is the Key tumbler. I have the exact same issue that you are experiencing with my ABS. I have replaced both the switch (box) and the key tumbler in recent years, but I am leaning towards the key as being the culprit. I have noticed that it is sometimes difficult to remove the key when I turn off the engine and think there may be a connection (pardon the pun) between the power and key removal issues...
 
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