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Help diagnosing ABS issue

wylde8
Posts: 4
Joined: Sun Nov 22, 2015 7:59 pm

Help diagnosing ABS issue

Postby wylde8 » Sat Apr 01, 2017 6:17 pm

I've been lurking here for a while, but an issue I'm dealing with is prompting me to make my first post. I have an 89 XJ40 with a 3.6 and the Bosch ABS system. I'm having an issue where I cannot bleed my rear brakes. I'm getting no fluid at all out of the bleeders. I traced the brake lines forward and found I have fluid going to the ABS pump / motor, but nothing coming out. Additionally, I have replaced the ABS pump / motor with a NOS unit, replaced the over voltage relay in the boot with a spare I had, replaced the ABS pump / motor relay, and replaced the ABS computer in the boot with another used unit. I pulled the cap off the connector to the ABS pump and found I have 12V going to both of the larger gauge brown wires, which it is my understanding are the power leads for the unit.

Can anyone offer me any advice or recommendations? I recently did a full mechanical restoration/refresh on this car front to back, and never would have guessed that the most difficult part would be the brakes.
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nlcrane
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Re: Help diagnosing ABS issue

Postby nlcrane » Sat Apr 01, 2017 7:55 pm

Not sure about this one, but check the inputs and outputs from the ABS unit. There seems to be only one relay for both back brakes, so this points to a common fault there. A fuse is shown in the overvoltage relay as well as a zener diode, both could be at fault, only you did state that you had installed another unit. Also check central fuse box, fuse number 6, although I am sure you will have already done this. Anyway, take a poke about using the signal levels shown in the schematics and get back to us. Lots of luck.

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ChrisW
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Re: Help diagnosing ABS issue

Postby ChrisW » Sat Apr 01, 2017 9:22 pm

There is one abs valve controlling the fluid to both rear brakes. It is possible that some contaminant has gotten into the valve block and stops that particular valve operating properly. This can happen if someone changes the pads and forces the pistons back into the caliper without bleeding off the excess fluid. Thus any dirt gets forced back up the line into the abs valve block. It is possible to disassemble the block and replace the faulty valve on the later teves system but I've not done it on the bosch system.
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wylde8
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Joined: Sun Nov 22, 2015 7:59 pm

Re: Help diagnosing ABS issue

Postby wylde8 » Sun Apr 02, 2017 12:01 am

Thanks nlcrane and ChrisW. I'm looking into the suggestions you gave me. As for a blockage, I can eliminate that as a possibility. The lines have all been flushed within the past six months, the brake hoses have been replaced, and all four calipers rebuilt.
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1989 XJ40

wylde8
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Joined: Sun Nov 22, 2015 7:59 pm

Re: Help diagnosing ABS issue

Postby wylde8 » Sun Apr 02, 2017 7:45 pm

nlcrane, where are you getting those spec sheets and diagrams? I have a Haynes manual, owner's service manual, and factory service manual, and I haven't found those in any of them. If its not from one of the manuals I have, would it be possible to email them to me? I'd like to make them larger so they're easier to see. Thanks for your help thus far!
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1989 XJ40

nlcrane
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Re: Help diagnosing ABS issue

Postby nlcrane » Sun Apr 02, 2017 8:35 pm

The schematics come from the Jaguar Classic parts DVD number JHM 1130, Supplementary Information 1987 – 1994. I don’t whether these are still available, but they can often be found second hand on ebay.

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SovverBovver
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Re: Help diagnosing ABS issue

Postby SovverBovver » Wed Apr 05, 2017 9:44 pm

Have you tried opening a bleed nipple on the rear caliper, turning on the ignition (with a good battery connected), then pressing the brake pedal?

Did any brake fluid come out?
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naki_k
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Re: Help diagnosing ABS issue

Postby naki_k » Thu Apr 06, 2017 12:50 pm

Replacing the over voltage relay and ABS ECU with an tier used parts will not necessarily cure a fault. Since most of these units all have the same issues.
Over voltage relay potentially can have a blown internal fuse. Also the standard dry joints/ cracked solder issue.
Likewise the ABS ECU will likely require resolderimg.
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wylde8
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Joined: Sun Nov 22, 2015 7:59 pm

Re: Help diagnosing ABS issue

Postby wylde8 » Thu Apr 06, 2017 6:46 pm

I'm hoping to do some more work on the car this coming weekend. There are a few more things I want to try.

SovverBovver, I have tried opening the bleeder and bleeding with the ignition on and the brake pressed, but no success. I've also tried using a hand pump, an air compressor driven bleeding kit, and the old fashioned up-down method with a helper in the driver's seat. No luck yet.

Even though a spare over voltage relay was installed, I'm planning testing it anyway. I doubt it will be at fault since the one currently in the car is a sealed relay, but I want to verify. As for the ECU, I haven't figured out a way to bench test it yet, but am hoping that since they very rarely go bad, at least one of the two I have will function correctly.
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1989 XJ40


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