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TD5 ABS sensor replacement


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#1 petrolhead63

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Posted 07 September 2008 - 08:55 PM

Hi, my 3 amigos idiot lights come on periodically, and a mate resets them on his pooter being told it is rear drivers side sensor. says intemittent sensor, and when lights stuck on no sensor!

So, now they are on and wont stay off so a new sensor is needed. Some people telling me put a whole hub in at best part of 200...ouch. There seems to be no bearing play so do these sensors come out reasonably or not?

Any tip please much appreciate.

#2 BogMonster

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Posted 08 September 2008 - 12:21 AM

You can buy cheap aftermarket sensors for a fraction of the cost of the genuine ones so I would take that route!
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#3 teabag

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Posted 08 September 2008 - 06:25 AM

Disco 2 ABS sensors are built into the hub so it's a replacement hub, where as the good old D1 sensors are external and only a tight push fit in their mountings and 'easy' to replace.
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#4 petrolhead63

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Posted 08 September 2008 - 07:50 AM

Disco 2 ABS sensors are built into the hub so it's a replacement hub, where as the good old D1 sensors are external and only a tight push fit in their mountings and 'easy' to replace.


after market sensors are available at about 35-45 each and according to the book they are held in by and allen bolt. That said I have with other cars learned they often corrode in tight and are a real git to remove.

Has anybody out there replaced a rear sensor only without renewing the hub?

#5 BogMonster

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Posted 08 September 2008 - 10:16 AM

I think they have done it at work but couldn't be 100% about that :unsure:
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#6 Ally V8

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Posted 08 September 2008 - 12:38 PM

Done lots,but my tip is to throw away the o ring and use a small smear of silicone instead - the o ring is tight and causes the bracket to bend very slightly,opening up the air gap.

#7 cipx2

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Posted 08 September 2008 - 02:53 PM

Here's my 2 (euro)cents ...

The "replace the entire hub if the ABS sensor needs changing" issue was introduced by LR much later than the D2 introduction on the market to address the potential problem of cleanliness when doing the job.

Here's the quote:

"Wheel bearing life and ABS sensor operation are significantly affected by dirt ingress into the bearing following replacement of the ABS sensor as part of a routine repair. Since the sensor is magnetic, normal cleanliness procedures will not prevent dirt ingress into the hub assembly and the effects will not be evident immediately following repair.

To prevent contamination, the ABS sensors will no longer be serviced as separate parts, instead being replaced as a complete hub and bearing assembly, refer to PARTS INFORMATION for specific details.
For the same reason, do not remove the ABS sensor at any time."


In other words, the ABS sensor can be replaced without the need of buying the entire hub assembly but LR no longer encourages this (since 2001).




Now, coming back to the ABS error, if the ABS computer shows an ABS sensor fault, it doesn't necessarily mean the ABS sensor is at fault and it needs to be replaced (specially when it's an intermittent fault, like the case here).
What the (SL)ABS computer 'sees' is a circuit which consists of connectors + wires + sensor and it sees it as a block (doesn't see the components of the block separately). There are 4 separate circuits, one for each wheel . The ABS computer declares a fault when the current through a specific wheel circuit isn't within some given limits (in fact, the current is 'translated' into a voltage measured accros a resistor inside the computer).

So, before blaming the ABS sensor, you should start with the rest of circuit which can be at fault from more common causes (which are also cheaper to fix): check/clean the connectors and test the wires (which can get broken in the jacket, for example). That is to avoid buying a new sensor and still have the ABS fault after replacing it.
The sensor itself is very simple inside: a coil over a magnet. It's very unlikely for the coil to get damaged, more likely the wires between the sensor body and the connector get broken. This can be tested with a multimeter (make sure to wiggle/bend/tension the wire while you do that) and can be repaired in most cases (if not all cases).

IIRC, the ABS sensor should have 1150 (-50 ... +100) ohms when measured across the terminals (anyway, it can be checked against the other sensors). Also, you should test that both wires are not shorted to ground (sensor's metal jacket).

There's also the chance that the sensor might be electrically good but not performing as supposed to (but it doesn't seem to be the case here). The causes might be the tooth ring too corroded/dirty, the air gap too big etc. You can get an indication of these causes by measuring the current 'produced' by the sensor on a test drive in a straight line (on the ground, not with the vehicle on axle stands - unless there's a locker on that axle which should be locked for this test) and comparing it with the one on the other (good) sensor on the same axle. A bit like these guys tried to do here but they should have used two multimeters (identical, if possible) for simultaneous reading on both sensors on that respective axle and the multimeter(s) should have been analog.

#8 Ally V8

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Posted 08 September 2008 - 06:31 PM

Here's my 2 (euro)cents ...

The "replace the entire hub if the ABS sensor needs changing" issue was introduced by LR much later than the D2 introduction on the market to address the potential problem of cleanliness when doing the job.

Here's the quote:

"Wheel bearing life and ABS sensor operation are significantly affected by dirt ingress into the bearing following replacement of the ABS sensor as part of a routine repair. Since the sensor is magnetic, normal cleanliness procedures will not prevent dirt ingress into the hub assembly and the effects will not be evident immediately following repair.

To prevent contamination, the ABS sensors will no longer be serviced as separate parts, instead being replaced as a complete hub and bearing assembly, refer to PARTS INFORMATION for specific details.
For the same reason, do not remove the ABS sensor at any time."


In other words, the ABS sensor can be replaced without the need of buying the entire hub assembly but LR no longer encourages this (since 2001).




Now, coming back to the ABS error, if the ABS computer shows an ABS sensor fault, it doesn't necessarily mean the ABS sensor is at fault and it needs to be replaced (specially when it's an intermittent fault, like the case here).
What the (SL)ABS computer 'sees' is a circuit which consists of connectors + wires + sensor and it sees it as a block (doesn't see the components of the block separately). There are 4 separate circuits, one for each wheel . The ABS computer declares a fault when the current through a specific wheel circuit isn't within some given limits (in fact, the current is 'translated' into a voltage measured accros a resistor inside the computer).

So, before blaming the ABS sensor, you should start with the rest of circuit which can be at fault from more common causes (which are also cheaper to fix): check/clean the connectors and test the wires (which can get broken in the jacket, for example). That is to avoid buying a new sensor and still have the ABS fault after replacing it.
The sensor itself is very simple inside: a coil over a magnet. It's very unlikely for the coil to get damaged, more likely the wires between the sensor body and the connector get broken. This can be tested with a multimeter (make sure to wiggle/bend/tension the wire while you do that) and can be repaired in most cases (if not all cases).

IIRC, the ABS sensor should have 1150 (-50 ... +100) ohms when measured across the terminals (anyway, it can be checked against the other sensors). Also, you should test that both wires are not shorted to ground (sensor's metal jacket).

There's also the chance that the sensor might be electrically good but not performing as supposed to (but it doesn't seem to be the case here). The causes might be the tooth ring too corroded/dirty, the air gap too big etc. You can get an indication of these causes by measuring the current 'produced' by the sensor on a test drive in a straight line (on the ground, not with the vehicle on axle stands - unless there's a locker on that axle which should be locked for this test) and comparing it with the one on the other (good) sensor on the same axle. A bit like these guys tried to do here but they should have used two multimeters (identical, if possible) for simultaneous reading on both sensors on that respective axle and the multimeter(s) should have been analog.

Yhis is all good advice,and very well put.A couple of months ago I was asked to look at a DII with all the lights on,RHF sensor erratic signal was the code that SLABS had stored.OK, have the hub apart after checking for bearing play,the toothed ring was clean / undamaged and all the conections were good.Fired up the scope and looked at both front sensor outputs,there was nothing to chose between them.We fitted a new sensor,still did not work.We cured it with a new hub.I guess main dealers were pointed in this direction after similar issues because of the very strict time allowance for each job.When the sensor wires snap inside the insulation the code is logged as "Sensor electrical failure" not low output or erratic output.

#9 Wingnut

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Posted 08 September 2008 - 07:21 PM

The rear near side hub was leaking on my D11, I thought it was the O ring leaking at first, so bought four second hand hubs through this web site.

All had had the ABS sensor wires cut on removal so I simply took out my ABS sensor from the leaking hub and put it back into the replacement hub. No problems since and no warning lights on the dash. Cleanliness is very important and a little grease on the sensor O ring aids refitting. It is very unwise to fit without the O ring because water ingress will start throwing codes in all directions and could eventually lead to bearing failure.

Don't mean to try and teach anybodys grandmother to suck eggs but a tip to the wise, if the rear of your brake disc is getting coated in oil, take out the sensor and see if it is coated in gear oil. If it is then the hub is leaking and not the O ring.

Peter

#10 petrolhead63

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Posted 08 September 2008 - 10:27 PM

[quote name='cipx2' date='Sep 8 2008, 03:53 PM' post='306383']
Here's my 2 (euro)cents ...

great advice thanks. I am prepared to remove he sensor if needs be and will clean the area and blow dry with an airline before removing it as some defense against dirt.

A couple of questions.

1) My mate is not on my doorstep with the diagnostics, which by the way are not land rover but are a serious bit of kit. If I correct the fault are the three lights likely to go out by self diagnosis it is all working without using the compuer, and the fault code of previous or intermittent fault can then be erased later?

2) to test the final part of wiring from last connector to the actual sensor for continuity, should I just prod the meter probe into the wire core through the insulation close to the sensor and check it back to the terminal on the plug?

many thanks.

#11 cipx2

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Posted 08 September 2008 - 10:52 PM

Don't remove the sensor before you test it for continuity (1150 ohms), no short to ground and test the wires starting from the SLABS computer if sensor appears to be ok (you need to disconnect the battery and the SLABS corresponding connector).

1) Most likely the warning light will extinguish after self test and 7 km/h, but the error will remain stored until it will be erased from memory (when you'll have the opportunity).

2) Yes, but only if there's no continuity with the probes at the sensor's connector and you want to try to repair it. Don't use the meter's probes but the thinnest needle you can find.

Good luck!

#12 JimAttrill

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Posted 09 September 2008 - 02:10 PM

We regularly remove the o-ring and give the sensor a 'technical tap'. Works in many cases. If it doesn't, we change the sensor.

About water ingress without the o-ring - well I guess it doesn't rain that much here as we have not had a problem with this.
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#13 Ally V8

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Posted 09 September 2008 - 02:29 PM

We regularly remove the o-ring and give the sensor a 'technical tap'. Works in many cases. If it doesn't, we change the sensor.

About water ingress without the o-ring - well I guess it doesn't rain that much here as we have not had a problem with this.

Would you like some rain Jim ? I reckon the UK population would happily vote to send you some,we are all fed up with it.The smear of silicone replaces the o ring,stopping any chance of water ingress,but does not bend the bracket.

#14 JimAttrill

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Posted 09 September 2008 - 06:21 PM

We wouldn't mind some rain now as it hasn't rained since about April. It's getting mighty dusty now and there are lots of veld fires which kill many animals. But one can't have everything in this world :)
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#15 petrolhead63

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Posted 09 September 2008 - 09:19 PM

We wouldn't mind some rain now as it hasn't rained since about April. It's getting mighty dusty now and there are lots of veld fires which kill many animals. But one can't have everything in this world :)

I like the sound of the technical tap.....that is right up my street!

#16 petrolhead63

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Posted 09 September 2008 - 09:40 PM

Don't remove the sensor before you test it for continuity (1150 ohms), no short to ground and test the wires starting from the SLABS computer if sensor appears to be ok (you need to disconnect the battery and the SLABS corresponding connector).

1) Most likely the warning light will extinguish after self test and 7 km/h, but the error will remain stored until it will be erased from memory (when you'll have the opportunity).

2) Yes, but only if there's no continuity with the probes at the sensor's connector and you want to try to repair it. Don't use the meter's probes but the thinnest needle you can find.

Good luck!


thanks again, if I test the resistance does the length of wire make much difference? for example if I test the whole harness from the slabs computer plug (unplugged!) am I still looking for circa 1150 ohms? If there is a broken wire I assume an open circuit is likely to appear. If it has a dodgy/dirty plug a high resistance.

If an open circuit or high resistance are found I can then work down the loom in sections/plugs untill the offending section is found.

Now a nice dry drive to lie on would be nice..haha

#17 cipx2

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Posted 10 September 2008 - 08:35 AM

No, no difference in resistance to worry about. 1150 plus or minus 100...150 ohms will still be ok.
The rest is ok.

#18 petrolhead63

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Posted 10 September 2008 - 05:33 PM

No, no difference in resistance to worry about. 1150 plus or minus 100...150 ohms will still be ok.
The rest is ok.

thanks again,l now I need to make the time and go to fiddle :rolleyes:

#19 petrolhead63

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Posted 16 September 2008 - 09:02 PM

No, no difference in resistance to worry about. 1150 plus or minus 100...150 ohms will still be ok.
The rest is ok.


well I've tried looking into it, but I am too thick to work out the wires on the computer end of things. (no wiring diagram yet!) The sensor tested 987ohms which is only just out of your tollerance. The plug is perfect and clean, and I can't find breaks in the wires so far but really need to find the computer end of the 2 wires so I can check continuity the whole way.

I took out the sensor and looked at it, it had a blob of grease on its end and grease can be seen on the ring looking in the hole......I assume this is normal. It also has marks on the end of the sensor but more odd is that it is not original, it has a cable too long coiled with a cable tie although it is correct in all other respects to look at.

The o ring stayed in the hole so I left it in place.

I would still be interested to have a definite answer if anybody knows.......if I try a known good sensor off another car will it need a reset to put lights out or will it self test and extinguish them. (the 3 amigos :lol: )

#20 cipx2

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Posted 17 September 2008 - 10:42 AM

987 ohms is ok. In LR schematics there's a 1k value so no worries here.

Here's the relevant schematic that you need:

Attached File  ABS_sensor_schem.JPG   87.14KB   252 downloads

Attached File  SLABS_connector.JPG   123.47KB   224 downloads




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