Ford Fiesta ABS Testing

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Ford Fiesta ABS Testing

Postby paul5082 » Tue Aug 01, 2017 4:50 am

Hi guys a bit new to the Pico, can anyone help? I'm trying to test the front abs sensor with the Pico and i'm struggling to find a pattern. I select ABS sensors under the Automotive sensor menu and select digital no reading, I have also selected Hall effect and still no reading. The sensor is a two wire sensor with a 12v supply (like the old inductive pulse). I have done some research and it looks like it should produce a square wave but as I have already mentioned I can't find any pattern. I was wondering if I have a setting wrong on the scope?
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Re: Ford Fiesta ABS Testing

Postby STC » Tue Aug 01, 2017 2:01 pm

That may be a GMT (Magneto Resistive)

It will have a very discreet square wave that rides on the 12v Supply Line, Easier if you use Vertical Zoom.
Alternatively look at it AC Coupled or with an Amp Clamp.

Of course if the sensor is faulty you wont see a thing so better start scoping a Known Good then revert to the suspect.
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Re: Ford Fiesta ABS Testing

Postby paul5082 » Wed Aug 02, 2017 5:39 am

Thanks for that STC.
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Re: Ford Fiesta ABS Testing

Postby STC » Thu Aug 03, 2017 8:58 am

paul5082 wrote:Thanks for that STC.


My pleasure. Did you find anything ?

Those position sensors are Sneaky little 8astards, they claim that the signal rides on the supply line, I would say they went to the trouble of "hiding" the signal on that line to mess with technician heads.
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Re: Ford Fiesta ABS Testing

Postby Martyn » Thu Aug 03, 2017 10:52 am

AC couple the scope to block out the 12V and you can see the signal in all it's glory.
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Re: Ford Fiesta ABS Testing

Postby STC » Fri Aug 04, 2017 8:52 pm

AC couple the scope to block out the 12V and you can see the signal in all it's glory.


Indeed Martyn, that was the only method available in the past, since "Vertical Zoom" has been a feature on the Pico I would say that now is a more conclusive method, for instance it will show a Voltage drop on the power line (if there is one) and the Signal "in all its glory" as you say.

Add an Amp Clamp to channel B and it really does paint a pretty picture of that sensor output.
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Re: Ford Fiesta ABS Testing

Postby Dave Hill » Fri Aug 11, 2017 11:21 pm

STC wrote:

Add an Amp Clamp to channel B and it really does paint a pretty picture of that sensor output.


That would have to be a very expensive micro amps clamp wouldn't it STC?

These magnretoresitive sensors produce a very subtle & rather messy / noisy signal in my experience (on these Fords in any case).
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Re: Ford Fiesta ABS Testing

Postby Technician » Sat Aug 12, 2017 12:23 am

Dave Hill wrote:
STC wrote:

Add an Amp Clamp to channel B and it really does paint a pretty picture of that sensor output.


That would have to be a very expensive micro amps clamp wouldn't it STC?

These magnretoresitive sensors produce a very subtle & rather messy / noisy signal in my experience (on these Fords in any case).


STC has just spent a pretty penny or two on a K110 :mrgreen: he's not finished yet :wink: wait till he gets the import duties from the main post office :shock:
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Re: Ford Fiesta ABS Testing

Postby STC » Sat Aug 12, 2017 7:42 am

Dave, Hi Stranger :)

That would have to be a very expensive micro amps clamp wouldn't it STC?


A misdiagnosis does not come cheap either !!! I work in full view of garage owners and technicians, No reception to hide behind. They lurk around !!

Indeed, it would have to be one that is suitable for the job, either that or loop a wire 10 or 20 times. We are in a precision industry, that makes sure that most instruments we purchase will draw cold blood and cause some short term pain. It is what it is.
I work on a No Find - No Fee basis, that clamp will pay for itself before it needs its batteries replaced :wink: :wink: It will provide graphical evidence of failure to my customer. I can be paid and long gone. I have no interest in waiting for a replacement Wheel Speed Sensor to arrive, let alone replacing it. I have a magnetic wheel made up to spin in front of it which will prove or disprove the magnetic ring it is looking at. Job done, belt and braces !!! Next !!!

I don't offer a fix, only a guaranteed accurate diagnosis.

My take on it is simple, either you are in it whole heartedly or you're not. Indeed I have spent fortunes on tooling and continue to do so.
On a brighter note I have not had to pay for premises, rent, rates .... ..... other than a £75 gazebo from Halfords.

These magneto resistive sensors produce a very subtle & rather messy / noisy signal in my experience (on these Fords in any case).

Horrible little 8astards is what they are! Regardless of the car they are fitted to. I see a fair amount on Maserati's and Ferrari's where they come complete with the hub at circa £700 a pop and they fail for fun.


STC has just spent a pretty penny or two on a K110 :mrgreen: he's not finished yet :wink: wait till he gets the import duties from the main post office :shock:

The odd item will slip through the net, however I will not be surprised if they stick a £50 bill up my shirt. I am prepared for that. Still not a bad deal I guess ??
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