Folks,
Any idea what the ABS sensor resistance (in Ohms) should be on my Vx Monterey?
On the vehicle it is reading 1007.
On the bench it is reading 1017 (and 1025 when the cable is moved).
(Not that au-fait with a meter, I wonder if I have the setting correct.)
Does this point to a duff sensor? The other side reads 1064 on the car. I have not taken it off yet and tweaked the cable.
Of course, interrogation of the ABS control unit would tell me straight away, but I don't want to pay dealer prices, and do not have one nearby. And I needed to assess the DIY potential of replacing the sensor anyway.
There has been a persistent problem with the ABS going off-line, usually following a right turn or suspension impact on the nearside. It was the nearside sensor that I took off the car today.
The fault went away for a couple of months after liberal spraying of corroded bolts (on the cable holder - not sensor!) with "duck oil" during disc replacement.
Any insights welcome!
Cheers
rg
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rg:
Don't know what the reading should be, but I'd suggest checking the resistance of ALL the others & if they are all the same, but different to the one you've checked then try to get a replacement sensor.
Don't go to Vauxhall. In my experience, they are pretty hopeless & would probably suggest a new abs unit & want to charge you a small fortune...
Good luck.
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Most abs sensors on cars have a resistance of approx 1000 -1500 ohms .the reading that you have is correct ,but when fitted to the car the cable twists & flexes and can possibly give you an open circuit condition which is enough for the abs Ecu to detect as a fault.
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Thanks,
No sign of open circuit on the one I took off the car.
Does the system detect a change in resistance, or a change in "pulses"? Can the pulse signal be masked by a high resistance?
rg
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r,
Resistance is the initial "crude" way of testing. When you start the car and the ABS light first goes out it is because the ECU checks by resistance that it can "see" all four wheel sensors.
Once you get rolling then the important signal is an ac sinusoidal waveform. Frequency determines speed but a poor quality waveform can cause the ECU to go to fault.
You need a proper diagnostic for a good waveform test but the voltage output can be roughly checked by rotating the wheel at one rev per second and looking for a specified voltage (usually between 0.25 and 2.0 volts).
To be honest the resistance test does show most faulty sensors but as you can see not absolutely prove it.
Ideally test the resistance from the ECU plug terminal that goes to the specific wheel sensor, that way you test all the wiring as well.
Front wheel sensors are the most likely problem.
Do you know the make/model of the system on your vehicle (eg. Bosch/Teves/Bendix). If so I may well have loads more info.
M.M
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hi mm
do you hvae any more of that info mine is a cav bosch system i think
could you send to pho@ntlworld.com
thanks in advance
phill
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A small current is induced in the sensor circuit by the 'teeth' on the wheel. This is compared with the other wheels and the ecu does the biz.
I have successfully tested a sensor on the car with a test meter capable of measuring microamps, or you can just about get away with milliamps. Jack up the car and pull apart the plug where the sensor joins the loom. Push in the meter probes into the sensor cable plug and spin the wheel. You should see the voltage pulses.
In your case I would suggest that there is bad continuity somewhere as I would not expect the resistance to vary whatever you do to the cable. This may cause the ecu to call foul and switch off the system.
If you have a decent scrappy near you I'd try replacement. You can test the scrappy one on the car using the above method. This worked for me with a Rover 820 and saved a good few pounds.
Please let us know how you get on.
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The ABS sensor acts as a small AC generator. The sensor consists of a small permanent magnet with a lot of turns of fine copper wire around it. As the 'teeth' of the ABS reluctor ring pass by, they cut the lines of magnetic flux from the sensor magnet. This in turn causes an AC voltage to be generated in the sensor wire.
Ideally borrow a 'scope to look at the AC output from each sensor as you spin each wheel. The waveform will be approximately sinusiodal. AC voltage is proportional to rate-of-change of flux variation and therefore will *increase* as wheel speed increases - the frequency of the AC will also increase of course (this is what the ECU is looking at).
Air gap between sensor and teeth is critical (mustn't be too large otherwise no signal detected at low RPM). Similarly, check for debris around sensor.
Wriggle wires to check for intermittent open circuit.
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To find out how to read your own ecu for free go to www.topbuzz.co.uk
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Thanks everyone,
Just for information, I throroughly cleaned the sensor heads and ring when changing the discs recently.
In view of possibile repalcement, I sprayed the sensor assembly bolts with "Duck Oil" (only stuff to hand at the time as I was away from base), and the problem seemed to disapper for a couple of months.
I suspect that this is pointing towards a breakdown of insulation on the leads to the sensor which the oil may have plugged. I will get the other sensor off this week and take a look for any damage.
All this "faffing" may result in me having to take it to a dealer for diagnosis anyway. ££££
M.M. - Manufacturer is Nippon ABS Ltd (??)
Thanks, all, once again.
rg
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If you've "cleaned up" the sensing surfaces I'd suggest to check the air gap again and adjust if necessary.
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r,
Pretty sure Nippon and Bosch are tied up somehow, a couple of their systems look identical. I've no specific data for you system, sorry.
All the above posted info is good but you are so likely to have a duff n/s sensor, from your "evidence", why not just take a chance and get one...or are they monster money for one of these?
M.M
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I had an intermittent problem with my Citreon Xantia (TEVES ABS) which,luckily, became a hard fault shortly after passing its MOT. The light would come on for a day or few days then clear itself. After the MOT it stayed on so, 5 months later, I decided to do something about it. Reading other threads in Honest John I decided to take it to a garage and have them wipe the memory and run a diagnostic. £53 later I was told that 3 of the 4 sensors were out of tolerance. I decided to replace all four sensors (preventative maintenance) but they only had one in stock. The resistance of the new one was 1105 Ohms. I replaced the front left and cleaned up the removed sensor. It looked OK and the resistance was 1097 Ohms. Fitted it to the front right. Checked the removed sensor and it was an open circuit - I think their comment of being 'out of tolerance' was somewhat economical with the truth! Started the car and the fault cleared and has remained clear for the last two months. Saved myself about £220 just by checking the sensor resistances. Would have done it before but, prior to the diagnostic, the information I had read pointed to a Computer fault (light on all the time). Hope my experience is of help.
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I could be a bit late on this topic...........
1997 Volvo V70.
My ABS light does not go out after the 2 seconds required by the UK MOT testing certificate. It does go out at 14-15 mph.
I have removed the main harness plug on the ABS unit and from the Haynes manual I've found the pins that go to each ABS wheel sensor. I did a resistance check on each sensor and my reading ranged from 1010-1050 Ohms on the four sensors. This would seem to be within a 10% of the mid point. I must now check the actual signal waveform from each sensor when the respective wheel is rotated.
Chris.
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The volvo has a notorious fault with the abs unit - can be fixed by resoldering the joints where the cable goes into the abs unit. otherwise talk to bba-reman for a replacement unit. try googling Im sure something will come up. I would say check the voc forums but they are titsup at the moment.
the fact that the light comes on when you are not moving says fault with unit not the sensor to my mind.
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The light is on when you are not moving is due most probably to the fact the fault codes are stored. If you clear these then the light will go out until the fault re-occurs when you are moving. Not sure on clearing codes on a V70 probably a 16 pin connector between the front seats in the storage box. This is a dealer code clear or needs to be done via a laptop.
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