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Old 23rd April 2017, 21:22   #1
-Joe
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Rover 75 Classic SE 1.8T

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Default Fixed my ABS problem

ABS light came on after slow hard left turn whilst parking.

Investigated Front left wheel. ABS wire had rubbed against metal wire protecting the brake hose and both red and yellow wires had been grounded to the car body earth.

I tried a replacement good sensor for front left. ABS light still stayed on.

I guessed ABS ECU was partially broken.

To fix it I

Went to a scrapyard found a diesel R75 checked it had no traction control and unscrewed the black front part of the donar cars ABS unit. 6x torx screws very difficult to get at.

Paid £2o for the ECU bit of an ABS.

Removing the ECU from my cars ABS was no fun at all. But it was possible without disconnecting any brake pipes. It just the position it's mounted in the car and how all the brackets that hold it obscure the torx screw heads. 2 man job one person needs to manourver the ABS unit about whist the other unscrews the six torx screws. I needed to remove the plenum side panel to get access.

Screwed new ECU in place, reassembled and everything works. ABS light gone and a wet grass test proved ABS is working.


Technical conclusion...

The ABS unit has 2 fuses. A large one 60 ampand a small 20 amp. The wires inside the ABS ECU are very thin. I havn't taken my old one apart but I bet one of those wires has melted through. The small fuse did not save the ABS ECU from short circiut damage. Maybe Rover wrongly specified the fuse value (20amp) for Rover 75 ABS. Anyone tried using a lower amp fuse for the ABS ECU and then testing the ABS still dynamically works and then shorting red and yellow wires to ground and seing if the fuse blows or it kills the ECU. An expensive and iritating series of tests that would prove if the Rover engineers overspecified the fuse that kills ABS ECUs. Or it could be a Bosche design fault in that ABS ECUs always die when you short any two of the speed sensor wires to ground regardless of the ECU fuse rating.
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