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Very odd ABS fault

Weso

Very odd ABS fault

Postby Weso » Wed Aug 17, 2011 8:51 pm

Hi guys,
Wasn't sure where to put this, so apologies if it's in the wrong place.
My '93 3.2S has a very strange ABS fault.
When starting her up the dash light goes out fine, however, when I turn hard right (mini roundabout or similar) it comes on, and will then go off when I straighten up the wheel again.
Occasionally the light decides to stay on continually after a right turn, but if I switch the ignition off then back on again it goes out immediately.
Any ideas where to start?
Regards
Wes

covkid

Re: Very odd ABS fault

Postby covkid » Wed Aug 17, 2011 10:30 pm

Weso wrote:Hi guys,
Wasn't sure where to put this, so apologies if it's in the wrong place.
My '93 3.2S has a very strange ABS fault.
When starting her up the dash light goes out fine, however, when I turn hard right (mini roundabout or similar) it comes on, and will then go off when I straighten up the wheel again.
Occasionally the light decides to stay on continually after a right turn, but if I switch the ignition off then back on again it goes out immediately.
Any ideas where to start?
Regards
Wes


Clearly your car has a 'dynamic' ABS fault.

I suggest you start with the Teves on-board 'blink test' to flag up any fault codes (cribbed from the J-L forum)

ANTI-LOCK BRAKING SYSTEM

On-board intermittent diagnosis (warning lamp blink display)

Ensure the ignition is ‘OFF’
Locate the PM4 diagnostic connector in the boot over the rear wheel arch close to the ABS ECU.
Insert a jumper lead between the black (ground) lead and the brown/pink lead
Turn the ignition key to position ‘II’ and observe the warning lamp
After six seconds, the blink sequence of the first code begins
Count the blink pulses and write down the resulting two-digit number
After a 6.5 second pause, the next code begins and so on until all the codes are read out and the warning light remains off.
Remove the jump lead and turn the ignition off

The fault codes are grouped in batches of nine (although all are not used)
– i.e. 11 to 19, 21 to 29, 31 to 39, … etc up to 71 to 79.
[The system will only identify one code from each batch on one ‘scan’ – the lowest numbered code in that batch. That fault must be cleared and the ECU re-set (by driving the car at a speed in excess of 19 mph) before the next fault code in a batch can be read by repeating the above procedure]

So the first number of flashes (blinks) you see will represent the ‘tens’, then a brief pause and then the second number of flashes (blinks) represent the ‘units’.
e.g. ‘blink blink pause blink’ = code 21
followed 6.5 seconds later by
e.g. ‘blink blink blink pause blink blink blink blink’ = code 34

Post the resultant fault codes to the Jag-lovers XJ40 Forum and a bloke on that will translate the codes for you.

richard moss

Re: Very odd ABS fault

Postby richard moss » Thu Aug 18, 2011 7:33 am

My guess is a break in one of the front ABS sensor wires. Whhen you turn the wheel it stretches/straightens the cable, breaks the connection and lights up a fault. Then as you straighten, the break remakes and normal service is resumed.

covkid

Re: Very odd ABS fault

Postby covkid » Thu Aug 18, 2011 8:11 am

richard moss wrote:My guess is a break in one of the front ABS sensor wires. Whhen you turn the wheel it stretches/straightens the cable, breaks the connection and lights up a fault. Then as you straighten, the break remakes and normal service is resumed.


Could be that - but the Teves test will tell him which one, so why guess?

richard moss

Re: Very odd ABS fault

Postby richard moss » Thu Aug 18, 2011 8:49 am

Indeed - but a bit of deduction (in addition to the test) will help - especially as the test will only display one fault per go.

nlcrane
Spain Rep
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Re: Very odd ABS fault

Postby nlcrane » Thu Aug 18, 2011 9:15 am

My guess would be that, for some reason, on a right hand bend / corner the gap between the ABS proximity sensor and the disc is increasing, the sensor’s magnetic flux lessens and this flags a failure in the ECU. When the wheels straighten up again the gap is again inside the tolerances, the flux increases and the fault is cleared by the ECU.
ImageImageImage
1994 Sovereign Gold 4.0

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old del boy
Posts: 6876
Joined: Thu Jul 10, 2008 9:29 am
Location: Kent

Re: Very odd ABS fault

Postby old del boy » Thu Aug 18, 2011 11:04 am

nlcrane wrote:My guess would be that, for some reason, on a right hand bend / corner the gap between the ABS proximity sensor and the disc is increasing, the sensor’s magnetic flux lessens and this flags a failure in the ECU. When the wheels straighten up again the gap is again inside the tolerances, the flux increases and the fault is cleared by the ECU.


Very good point Norman , similarly a badly adjusted or knackered bearing can set up vibration which will also cause interference to the signal , a loose fitting sensor which causes the air gap to fluctuate or a broken wire as Richard has suggested will all cause a fault to be flagged , in fact from what i've seen of the fault codes most are related to sensors , as this only occurs when turning corners would i feel it narrows it down to the front wheels ,

Derek..
'93 4.0L Daimler, solent blue,
'93 4.0L Daimler, Westminster,
'85 2600 Rover sd1 vdp oporto.

sovereign-dave
Posts: 590
Joined: Fri May 15, 2009 6:28 pm
Location: Selsey, West Sussex, PO20

Re: Very odd ABS fault

Postby sovereign-dave » Thu Aug 18, 2011 9:23 pm

I had the exact self same fault on my 1994 Majestic. I thought it was a wheel bearing / air gap fault on one of the abs sensors. The abs light would only come on going round tight right hand bends. I stripped all hubs and found no fault
I traced the fault to a faulty abs ecu in the boot, I swapped it for another one and the problem was cured for good.
Strange but true.
I hope this helps.
Dave.
Image

'94 3.2 XJ6 Gold, Sapphire Blue. 708694 !!

naki_k
Super Moderator
Posts: 28912
Joined: Sun Feb 21, 2010 9:25 pm
Location: Kirton, nr Boston, Lincolnshire

Re: Very odd ABS fault

Postby naki_k » Thu Aug 18, 2011 10:10 pm

sovereign-dave wrote:I had the exact self same fault on my 1994 Majestic. I thought it was a wheel bearing / air gap fault on one of the abs sensors. The abs light would only come on going round tight right hand bends. I stripped all hubs and found no fault
I traced the fault to a faulty abs ecu in the boot, I swapped it for another one and the problem was cured for good.
Strange but true.
I hope this helps.
Dave.


interesting. must be worth a shot, as its such a simple swap over. take 2 minutes.
they dont fail that often do they? not heard them discussed that much before?
88 3.6 XJ6 PDH/CEM
90 Range Rover Vogue SE 3.9 V8 LPG
91 4.0 XJ6 Manual
92 4.0 XJR Manual
92 4.0 XJR
93 3.2s - 4.0 Manual conv
93 4.0 Sovereign
93 6.0 XJ81 DD6 x2
93 6.0 XJ81 XJ12
94 4.0 XJR
94 4.0 Daimler
96 4.0 X306 XJR
96 4.0 X300 D6
97 4.0 X300 Sport Manual
2000 LR Discovery ES TD5 A
Breaking 40/ 300


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