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ABS Computer saga

Discussion in 'How-To' started by bkaul, Nov 23, 2009.

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  1. bkaul

    bkaul Member Established Member

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    Posting this in case it helps anyone who runs into similar issues:

    A while back, I started seeing my ABS light come on intermittently on my '01 Cobra (daily driver, 205,xxx miles). Not a huge deal around town in late summer, but not something I wanted to leave broken either. Bought an ABS code reader to troubleshoot the problem. Well, when the ABS light was on, it wouldn't communicate with the computer at all; while the ABS light was off, it would communicate and said there were no problems. My OBD-II scanner never had difficulty connecting to the PCM throughout this ordeal, so I was sure this wasn't a problem with the connector/wiring under the dash.

    I have a set of factory service manuals for the car, so after checking all the relevant fuses (there are several), I started going through all the troubleshooting steps they have, checking the wiring between the ABS controller and the diagnostic connector, etc. After a few minutes, I got to where the next step in any of the troubleshooting procedures was to R&R the ABS Electronic Control Unit (ECU) and try again.

    So, I run over to the local Ford dealer and inquire with their parts department about getting a new one ... they really think highly of that part, it seems: wanted over $1000 for it. That seemed a bit steep, so I bought one on eBay for about $150 (actually, included both the Hydraulic Control Unit (HCU) and ECU, rather than just the latter).

    Looking at how this is all mounted up, the ECU is mounted to the end of the HCU/pump assembly, and there's a bracket holding it to the passenger side fender under the air filter. I determined that if I took the bracket off and left everything hanging by the brake lines, I could remove the ECU from the HCU without breaking into the brake system and having to bleed the brakes. This was a good plan. Unfortunately, in the course of my exploration, I damaged the wiring on the hydraulic pump and ended up having to replace the entire ABS control assembly.

    Here's where I should've stuck with my original plan and done it in parts: In the process of installing the new (used) ABS control module, some brake fluid leaks out of the brake lines and runs all over the place, including down into the ABS ECU. So far as I can tell, this is unavoidable if there's any brake fluid in the system (which there will be). It turns out that brake fluid does a nice job of eating the insides of the ECU over time ... so after putting everything back together and bleeding the brakes, I was good for a couple of days, but then started getting an ABS light again. :cuss:

    This time, the code reader would communicate just fine with the ABS controller: it was reporting a circuit fault on one of the wheel sensors (front right IIRC). After a few more days, when I checked it, it was reporting a circuit fault on two of the wheel sensors (front right and rear left). I'm pretty confident at this point that there's no way I could've damaged two opposite wheel sensors or the associated wiring without knowing it, so the recently replaced computer must be at fault. But, ABS not being an urgent drivability concern, I figure I'll get around to fixing it again later and just keep driving it. I figure I know how to drive safely without ABS (do it all the time in the '84), and I don't have to bother turning off the TC this way (when the ABS is on the fritz, it gets disabled automatically) ... most annoying thing is really the yellow light on the dashboard being on; I'll get around to it later.

    Well, the brake fluid wasn't satisfied with eating those parts of the computer. It moved on and shorted out more of the internals, so that fuses blew and my brake lights went away! :eek: OK, now it's urgent.

    The fuse under the dash that the manual indicates is for the brake lamps was fine. I found that one of the under-hood fuses for the ABS was blown (one of the little 20-amp minis); replaced it, and it instantly blew again, with a puff of smoke coming up from the ABS controller. Unplugged the ABS computer electrical connector and replaced the fuse again; didn't blow, but still no brake lights. I was assuming at this point that the signal for the brake lights was routed through that computer such that the connector had to be in place for them to work. (I would later find that there was another blown fuse that I hadn't discovered yet.)

    So I turn the '84 into my daily driver for about a week until I can get this problem really fixed: I'm willing to drive without ABS, but having no brake lights is extremely unsafe. The Cobra gets to nap in the garage until this is sorted out. I found another ABS controller on eBay (even better deal this time - $80 shipped), and replaced just the ECU, leaving the HCU in place according to my original plan (didn't break into the brake lines). Replaced the underhood fuse again, plugged everything back in, and no more ABS light, but still no brake lights ... crap.

    The interior fuse for the brake lamps wasn't blown. After a few minutes of confusion, I noticed that the stop lamp switch (on the brake pedal) has a separate fuse from the brake lamps themselves ... weird. Turns out this fuse had blown when the ABS controller shorted out. Replace that, and all's good again. I have brake lights, no warning lights, and the ABS/TC work in test drives. Haven't had any problems recur yet in the half-week since I got that sorted out.

    So, lessons learned:

    • If the ABS ECU fails, you should get the mounting bracket out of the way and replace it without removing the HCU.
    • If you must replace the HCU, remove the ECU from it until the brake lines are attached and everything's cleaned up, then install the ECU as above.
    • Ford wants way too much for that part: eBay came in most helpful.

    Note: the ABS module for the Cobra (with T/C) is not the same as the one for lesser Mustangs (no T/C). The Mach 1 and other special products appear to mostly have the Cobra unit; it's easy to tell from pictures in any case: the one you want says "COBRA" in big letters on the label on the ECU. AFAIK, '99-'02 modules are identical; not sure about earlier or later years.
     
    Last edited: Nov 24, 2009
  2. Janstang

    Janstang New Member Established Member

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    Good info.. Thanks for the post.
     
  3. birdman941

    birdman941 Illiterate Proofreader Established Member

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    Interesting thread.
    If the OP could post pics and show where and/or how the HCU and ECU
    are separated, maybe specific locations for the fuses,
    it would be perfect, and definite sticky material.
    As Cobras and Mach 1's age, this would be excellent info to have
    at one's fingertips.
    Bravo.
     
  4. bkaul

    bkaul Member Established Member

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    More details, with pics ... didn't take time out for photography during the job, but snapped a few of the old parts after the fact.

    It's not even necessary to jack the car up to do this one (unless you change the HCU and have to bleed the brakes).

    First, release the electrical connector by pulling the handle in the direction indicated, then disconnect and move the harness out of the way:

    [​IMG]

    There are two 13 mm nuts holding the HCU to the bracket, two 13 mm nuts holding the bracket to the fender, and one 10 mm bolt on the bottom of the bracket. Loosen the nuts holding the HCU to the bracket (it's not necessary to remove them entirely: the bracket is slotted)

    [​IMG]

    Remove the two 13 mm nuts holding the bracket to the fender. The one towards the front of the car is most easily removed with a socket, u-joint, and a couple of 8" extensions (or maybe more easily accessible with a wrench if the air box/filter is removed first). The back one is a straight shot.

    [​IMG]

    From underneath the car, remove the 10 mm bolt holding the bracket from the bottom. The mounting bracket should now slide off the studs in the fender and down off the ABS controller, which will remain hanging from the brake lines.

    Unplug the electrical connector between the ECU and the hydraulic pump. Do not mess with the end that's held to the pump motor with Torx screws; unplug the end at the ECU.

    [​IMG]

    Six T-20 Torx screws hold the ECU to the HCU. It's symmetrical, with screws located where shown here (screws already removed):

    [​IMG]

    The top and bottom pairs of screws can be removed with a socket/ratchet if desired; the middle pair don't have sufficient clearance for a socket: a screwdriver-style Torx tool is required to get to them. The screws are accessible from under the car, where you removed the mounting bracket.

    Remove the 6 Torx screws, and the ECU will easily pull off the end of the HCU.

    [​IMG]

    Installation is the reverse of removal.

    If it's necessary for you to R&R the HCU, do so without the new ECU in place: the brake fluid that will certainly drip from the lines will damage it otherwise. After you've got the new unit connected and cleaned up, install the new ECU, etc. It will be necessary to bleed all the brake lines after replacing the HCU.

    The plausibly related fuses according to the manual include #s 8 & 17 under the hood and #s 29 and 35 inside for the ABS module, and #s 33 and 41 inside for the stop light switch / brake lamps. In my case, # 17 under the hood and # 33 inside blew when the second computer shorted out. The first time around, all the fuses were fine.
     
    Last edited: Jan 5, 2010
  5. 3B99SVT

    3B99SVT Top down makes me smile Established Member

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    How did you bleed the brakes to make sure all the air was out of the HCU? I've tried the traditional method and can't seem to get it all out. I took it to Ford a while ago and they said I need a new $1100 ABS brain since mine wasn't communicating w/their machine to cycle the ABS to purge the HCU.

    I'm thinking of getting one of those bleeders that force brake fluid from the caliper up to the master cylinder. The manufacturer claims it helps remove air bubbles even out of ABS systems with the reverse flow. Has anyone used one of these?
     
  6. bkaul

    bkaul Member Established Member

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    I have a vacuum brake bleeder - hooks up to an air compressor and draws a vacuum; attach it to the bleed screws and it will suck fluid through. A bottle that works kind of like an automatic pet watering bowl sits on the brake fluid reservoir to keep it filled to the proper level as the brake fluid is flushed/bled.

    I bled the system from all four wheels, and also from the two MC bleed screws. Not sure whether the latter was necessary, but figured it couldn't hurt. Getting a good seal on the bleed screws is tougher on the front calipers than the rear; after applying a bit of silicone vacuum grease, though, it'll seal up and not pull in air at the screw (which would cause deceptive bubbles in the hose that didn't actually come from the brake system, making you think you're not done even if you are).

    It took a lot longer on each wheel than bleeding a new caliper or even flushing old brake fluid, but it eventually seemed to get all the air out (fluid running clear & continuous in the hose, w/o all the bubbles), and on my test drive afterward, the pedal felt firm and the brakes responded as if properly bled, so it seems there's no more hiding in there. I probably flushed the system about 3x over in the process as measured by quantity of brake fluid, but it eventually bled out.
     
    Last edited: Nov 24, 2009
  7. birdman941

    birdman941 Illiterate Proofreader Established Member

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    Awesome writeup.
    Sticky material.
     
  8. 3B99SVT

    3B99SVT Top down makes me smile Established Member

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    Wow! That brake bleeder looks nice. The cheapest one I saw on eBay was over $300. I like the idea that there are no pulses that give an air bubble time to return to a high point. How much would you charge to bleed my brakes if I drove up sometime? I've always wanted to run the Tail of the Dragon on the west side of the Smokeys. And I did forget to mention -- nice info and write-up!
     
  9. luiSVT99

    luiSVT99 CoyoteFTW Established Member

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    Definetly a STICKY! :beer:
     
  10. tangelaccio

    tangelaccio New Member Established Member

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    Bkaul, question for you. I have the same problem with my 01 Cobra, ECU is not working, no error codes, just intermitent ABS light coming on. I need to remove only the ECU but couldnt get to the screws to do so. If I remove the HCU bolts and lift up the HCU will I be able to rotate it enough to remove the ECU? Will the brake lines give enough without damaging anything?
    Great write up and pics by the way.

    Tony
     
  11. bkaul

    bkaul Member Established Member

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    Tony,

    You can't really bend the HCU around very far without kinking the brake lines, but if you remove the mounting bracket and leave the whole assembly just hanging from the lines, you should be able to get to the screws that hold the ECU onto the HCU from under the car/through the passenger side wheel well. (Lying in the same position you need to be in to remove that bottom bolt on the bracket and pull it out). There's enough flex in the lines to push the bracket off the studs, etc. but I wouldn't want to try to force anything as far as actually twisting the control unit around into a different orientation.

    You won't be able to reach the screws that hold the ECU on from the the top past all the brake lines, except for maybe the top two. I took all of 'em out while lying underneath the car after removing the bracket. For the top pair of screws, I had to use a Torx socket on a 1/4" drive ratchet; for the middle pair, I had to use a screwdriver-style Torx driver since the socket wouldn't fit down in the gap between the computer housing and the wiring connector; the bottom pair is accessible with either style tool. I had to hold the flexible plastic splash guard in the wheel well out of the way with my other hand to make space for the screwdriver-style tool to clear, but didn't have to actually remove it.

    Brian
     
  12. Brutal Metal

    Brutal Metal Well-Known Member Established Member

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    Is there a way to easily just disconnect the ABS??
     
  13. tangelaccio

    tangelaccio New Member Established Member

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    I'll give that a try....jack up the car and not remove the wheel well cover and reach from the under side to remove the HCU bracket and then the ECU.
    My ABS light has been on steady for 6 months now. When I disconnected the battery and ECU connector to try and remove then re attached them the ABS light is back to staying on for 15 minutes then off again, strange.

    I found some places on line that I can ship my ECU to that will repair it and send it back so I'm going to give that a try. CheapABS.com is the one I'm going to try first. $99 plus shipping to repair and they work on Bosch 5.3 and 5.4 so should be able to repair the Cobra ABS.

    You have alot of miles on your 01, any other issues with that many miles?
    I just hit 115k and hoping to keep her for as long as possible.

    Thanks Brian
     
  14. brkntrxn

    brkntrxn Inappropriate Motorsports Established Member

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    Great information. Excellent post.


    This needs to be moved to the "How To" section for certain. I'll PM Barry.


    -Kevin
     
  15. bkaul

    bkaul Member Established Member

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    Disconnect electrically: just unplug it ... your indicator light will always be on though, since the ECM or IP or whatever controls that indicator can't communicate with the ABS controller.

    Disconnect hydraulically too: you'd have to run new brake lines from the MC to the wheels ... not sure why you'd want to eliminate the ABS, but it's not impossible.
    If your car's not lowered you may not even need to jack it up; I was able to get in there with the car sitting on the ground.
    Ah, good resource to know about. I'll have to remember that in case mine goes out again in the future.
    Nothing major, really ... I've had to replace the rack (inner tie rod end started leaking), a sway bar link, a ball joint, a couple wheel bearings, etc. but nothing unusual. Obviously brakes/tires/filters/belt/etc. have been changed repeatedly (I'm just about to turn over 209,000). Factory battery hasn't even given out yet, though it's got to be getting close. There's a thread here where people are discussing how many miles they've got on 'em. If you take care of these cars, they'll last a very long time.
     
    Last edited: Jan 5, 2010
  16. bkaul

    bkaul Member Established Member

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    Thanks!
     
  17. Black*Death

    Black*Death Sleeping Established Member

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    I'm interested in possible rebuild also..let me know how they do for you.
     
  18. tangelaccio

    tangelaccio New Member Established Member

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    I'll let everyone know how it goes when I get to taking the ECU out and get it repaired.

    I found 3 places that repair them: +shipping

    1. CheapABS.com ($99)
    2. modulemaster.com ($160)
    3. bba-reman.com ($179)


    All were cheapier then buying used and I read you didn't have to re program the module once you re-installed it, something about having to do that if you got a new or used one.
     
  19. bkaul

    bkaul Member Established Member

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    If you get a used one from the correct vehicle (or a new one from the dealer that's been programmed by Ford), it's just a matter of installing it. If you got the same Bosch hardware from a different car, it would need to be reprogrammed.

    I found a used module on eBay for less than they're charging, but it's hit and miss ... definitely looks like a worthwhile resource! Looking forward to hearing how it works out for you.
     
  20. Bnasty

    Bnasty New Member Established Member

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    Hey guys,
    I have the same system failure, taking it to a garage and scanned for free turned up a "cannot communicate with ABS module". I have diagnosed it per the cobra shop manual, and I get "less than 5 ohms resistance" from the designated pins on "harness side" (This procedure is outlined in Pinpoint test A, page 7 of the PDF, if you get a chance, please skim over the troubleshooting and let me know what you think).

    Now, why on earth would you test the "harness side"? Wouldnt you need to test the module itself? It makes no sense to me, but it definitely confirms the previous OBD scan saying that it wasnt communicating. Where does the harness side run? Does it go to the main ECU for the entire car? What gives??
     
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