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!
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:
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.
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!
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:
