Mud-club
Vehicle & Technical => Discovery => Topic started by: trec 2 on August 10, 2006, 18:49:22
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Im sure this has proberbly been done before, but is there any way of 'testing' the ABS system to eliminate faults at the hubs without the need to plug it into a computer (at a cost of £70 a time).
The initial diagnosis indicated an ecu fault (that has been replaced with a 2nd hand one) and open circuits on three wheels.
Suggestions to date have included some sort of shorting out and counting the flashes, or a method using a test meter. Neither of these have been anything more than 'I'm sure you can' types without the explaination of the finer details.
Many thanks
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To test the wheel speed sensors at the hubs:
Dis-connect the sensor and measure the resistance of the sensor with a multi-meter.
Now, I'm not sure of the exact resistance for the sensors, but checking all 4 should give you a rough idea (around 8-10ohms I think). Obviously if the sensor is open circuit (has no resistance) then it's dead!
If the sensors all read roughly the same, then you need to reconnect the sensors and test the resistance of the sensor wiring/circuit. Unplug the ABS module multi-plug and put the meter across each of these pairs of wire connector pins, noting the resistance figure:
LFront=15&32, RFront=17&34, LRear=18&35, RRear=16&33
(Assuming a 96/97 Tdi)
An alternative way to test each of the wheel sensors is, jack up the wheel, chock the other 3 and let the handbrake off, set the test meter to AC volts and whilst you're holding the wires in the connector get an assistant to spin the wheel, you should get a voltage that rises as you spin the wheel faster.
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I don't know much about Discovery ABS, but the article on ABS Fault Diagnostics and Codes (http://members.mud-club.com/library/?articleid=19) in the Workshop section of Mud Club may well be appropriate for your car. Have a look at it and if the components pictured are the same as those on your car it's probably the answer you're looking for.
Regards
Wolfie
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The proceedure in the workshop does work, but it needs updating really. On mine the ABS diagnostic plug has been integrated into the OBD2 plug at the top of the footwell. You need to find the right wires to join together, cant remember off the top of my head what they are though.
Also, you need to clear all the codes stored, then drive the car, then read the codes again. I had 4 on mine, I was trying to sort out the first fault reported by replacing an ABS sensor but it had already been sorted by a previous owner. After I cleared the codes and then re-read them, I only had one fault come up, 5 minutes later it was sorted.
Peter