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Topic: Any ideas? ABS sensorloom picks up unwanted DC (Read 508 times) |
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Cosray
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8th Scorpio, 2nd Cosworth: currently '95
 
Posts: 569
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Any ideas? ABS sensorloom picks up unwanted DC
« on: Dec 5th, 2008, 1:40pm » |
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Scorpio 24v Cosworth 95
Recently had persistent ABS error after error.
OBD indicated RH rear sensor fault.
Replaced both RH front & rear sensors; everything dry and clean and around 1050 Ohms measured at sensor as well as at disconnected multiplug contacts.
Reset errorcodes; kept popping up; ABS/TCS light on.
Each sensor connects to the ABS module in front through a floating symmetrical wirepair in the loom, thus eliminating stray spikes and interference for a clean pickup-coil signal.
Disconnected multiplug under ABS pump as well as sensor connectors.
Then astonishingly measured 13V against ground on the brn/grn wire of the supposedly floating wirepair for sensor RH rear!
The other 3 sensor linepairs are floating and DC-free!
Apparently coming from some highresistance source from the loom as a 100 Ohms resistor against ground leaves .1 V. Max. current drawn against ground is around 5 mA.
Reconnected multiplug and sensorconnectors, leaving 100 Ohms resistor on the brn/grn wire to ground.
The sensorcoil resistance now allows the voltage to be on both wires of the - supposedly - floating wirepair.
ABS light will extinguish after drivespeed over 15 km/h but comes on again while braking at low speed, actuators to be felt and heard.
When the grounding resistor is removed the linevoltage against ground is a constant (!) 2.32 V! This may be due to the input properties of the connected ABS module, drawing current from the linepair.
Has anyone come across similar strange behaviour, where from the loom a voltage is leaked onto the floating linepair (pins 9 & 10 on the open multiplug) for the RH rear sensor?
Where does this highly unwanted voltage originate?
Any clues are wellcome as with this stray DC-component on the linepair ABS cannot ever function properly.
Curious,
Ray
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