Xantia ABS light staying on

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den
Posts: 20
Joined: 04 Feb 2001, 20:19
Location: United Kingdom
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Xantia ABS light staying on

Postby den » 28 Aug 2002, 16:09

The ABS light on my 1995 TD SX is staying on.Looking back through previous postings I found very useful info posted by Dave Goddard (thanks Dave)Using the info given by Dave I tested the wheel sensors with a meter at the multipin plug end.The results are:-
F.N.S. pins 15 & 30 =1089ohms
F.O.S. pins 1 & 6 = 0 (no reading)
R.N.S. pins 28 & 19 =1092ohms
R.O.S. pins 29 & 31 =1097ohms
Dave indicated that the readings should be about 1500ohms.Having no reading on F.O.S. seems to indicate that this is where the problem may be.The fact that all the others are giving similarly close readings, I would appreciate any comments regarding if these readings are too low or satisfactory.If all else appears satisfactory would replacing the F.O.S. sensor be likely to cure the fault.What would the part number be for this at Andyspares.
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alan s
RIP 2010
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Postby alan s » 28 Aug 2002, 18:22

I would say FOS is the culprit. Regards the readings, I wouldn't lose too much sleep over them as my personal thoughts rightly or wrongly would be that if the balance are pretty even, then it is fair to assume they are all OK.
When you replace the sensor, I suggest that you clean the serrated wheel on the one being replaced and the other three as well as they do have a tendency to get covered in grime & muck which does tend to throw the readings a bit. This 'may' bring the readings within the figures quoted by Dave (if he reads this he probably will confirm.)
I don't profess to be any authority on these but I have proven with my car that a good cleaning as part of a general service does make one big difference. Possible cause of failure as per the ones I've experienced so far seems to be an internal break in the wire.
Alan S
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NiSk
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Joined: 24 Jan 2002, 21:11
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Postby NiSk » 28 Aug 2002, 18:30

Before going to the expense of buying a new ABS sensor, try checking out the wiring. Follow the lead from the sensor (on the hub) until you come to a joint (connector) pull the connector apart (If a previous owner/garage hasn't already soldered it up) and check the resistance across the lead to the sensor. Very often, there's no fault in the actual sensor, just a dodgy connector. I've even had wires worn through (i.e. open circuit) due to someone moving the cable to get at something else and then fogetting to put it back!
By the way, around 1kohm is O.K.
//NiSk
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David Goddard
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Postby David Goddard » 31 Aug 2002, 13:50

No worries - I must have transposed some digits. I have just re checked a spare sensor it measures 1,090 ohms. A very much higher reading could indicate a dirty connection. No reading (infinity) is open circuit fault.
The sensor wires are very fine so are likely to go open circuit. The cables to the sensor are extremely tough and routed to avoid damage so I would gamble on sensor failure.
My spare sensor? Well it's not exactly spare - the coil is OK but the magnetic core got bent. Possibly due to a stone becoming wedged between the it and the toothed wheel. The consequence is that the output voltage is 50% down compared with the other wheel.
How do I know this? I have recently been suffering with the ABS warning light going on intermitantly. So I checked the sensor resistance - all OK, then thought I would check the voltage with a scope. Turning a wheel at 1/4 rev per second gives about 160mV (peak to peak) - what a sad life!
Anyway dispite replacing the bent sensor, I still have an occasional warning light problem. I found that this can be switched off by turning the ingition off and removing the multi pin connector on the ABS ECU for 10 seconds. The after driving for a 100m or so, the self diagnostics routine is happy and the light goes out.
It's going to my local dealer for a diagnostic check next week so I will see what they can find.
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den
Posts: 20
Joined: 04 Feb 2001, 20:19
Location: United Kingdom
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Postby den » 31 Aug 2002, 19:44

Many thanks for the info David.This has really helped me a lot.I haven't yet checked to see if this is a wiring or sensor fault yet.Will post an update asap.Looking forward to your next thrilling installment !
DEN
No worries - I must have transposed some digits. I have just re checked a spare sensor it measures 1,090 ohms. A very much higher reading could indicate a dirty connection. No reading (infinity) is open circuit fault.
The sensor wires are very fine so are likely to go open circuit. The cables to the sensor are extremely tough and routed to avoid damage so I would gamble on sensor failure.
My spare sensor? Well it's not exactly spare - the coil is OK but the magnetic core got bent. Possibly due to a stone becoming wedged between the it and the toothed wheel. The consequence is that the output voltage is 50% down compared with the other wheel.
How do I know this? I have recently been suffering with the ABS warning light going on intermitantly. So I checked the sensor resistance - all OK, then thought I would check the voltage with a scope. Turning a wheel at 1/4 rev per second gives about 160mV (peak to peak) - what a sad life!
Anyway dispite replacing the bent sensor, I still have an occasional warning light problem. I found that this can be switched off by turning the ingition off and removing the multi pin connector on the ABS ECU for 10 seconds. The after driving for a 100m or so, the self diagnostics routine is happy and the light goes out.
It's going to my local dealer for a diagnostic check next week so I will see what they can find.

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