Abs light

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Steve Smith
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Re: Abs light

Post by Steve Smith »

Hello and thank you for the feedback

“I’m not sure that it refers to speed sensors, looking on the internet you can find only that error description.”

This concerns me as we must understand the description of the code or we are diagnosing parts of the ABS system that may not be relevant to the fault.

If we prove the DTC relates to wheel speed:
Could we confirm wheel and tyre are the specified diameter, tyre configuration/circumference are the same and check for any recent wheel bearing replacements. (Aftermarket ABS sensors spring to mind too)

I have checked the waveforms sent and have questions about the captures:
Image 1
Image 1
Maths has been applied to the above capture but heavy filtering was required. It also looks as though we may not have a minimal wheel rotation (at very low speed) and so I would not like to rely upon the above capture


The capture below would appear to show differing signals from sawtooth to square waveform.

Channel B is also at 5.99 V whereas the others settle around 12 V!?
Could you confirm if this is a measurement error as we did not see this effect in the capture above?

Could you confirm if you are measuring across the ABS sensors?
If so, ideally, we need to measure with reference to ground

Each waveform below demonstrates a “disturbance”; however, Channel D seems to be affected more than the others
Image 2
Image 2
If we can confirm ABS speed signals are the reason for our fault code, we are going to have to pursue this using current in order to obtain the best possible display of our signal.

The output from these sensors is very small (5 to 15 mA) and so using a milli-amps clamp or coil multiplier is going to be required with repeated, identical road tests (If one current clamp is available)

This Case Study describes the technique

I hope this helps take care……Steve

Emanuele.Vag
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Re: Abs light

Post by Emanuele.Vag »

Hello everyone. I checked the sensors at a higher speed about 25 km / h.
the frequencies were the same in all four sensors.
we decided to replace the abs module.
the error disappeared, although with a bit of disappointment because I was unable to understand what was the origin of the problem.

Steve Smith
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Joined: Sun Aug 25, 2013 7:22 am

Re: Abs light

Post by Steve Smith »

Hello and thank you for the feedback, it is much appreciated and will serve to assist others

Regrading the original fault code, was the supporting information acquired from the manufacturer portal or from a 3rd party supplying technical information

It would be great to link the detection condition of the fault code to the replacement component and perhaps understand why this is now cured

Thank you once again for taking time to feedback, take care......Steve

Steve Smith
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Re: Abs light

Post by Steve Smith »

Following on from the discussion above surrounding ABS pump operation and the internal “Self-Test” procedure, thanks to Kevin at Ives Garage I had the opportunity to visit a vehicle with one such fault.

The vehicle in question is a 2002 Honda Jazz with an ABS fault code “51” with the description “Pump Motor in Hydraulic Modulator” (Test not successful)

The component had already been diagnosed (ABS pump/Modulator assembly) however, prior to fix, here is an opportunity to understand how and when the ABS pump motor test is carried out by the ABS system

Below we have the PicoScope 4823 monitoring multiple ABS inputs/ outputs capturing the moment the ABS warning light is activated
Pre fix
Pre fix
Prior to driving the vehicle, the ABS code had been erased, the ignition cycled and upon restarting, the ABS light extinguishes as normal. At this stage the ABS system is happy with all relevant inputs.

As you can see in the above capture, driving vehicle from rest results in the near immediate illumination of the ABS warning light (Channel G)

Note, that during this very short and low speed journey Channel A has not seen a momentary increase in current in order to operate the ABS pump (Self-test)

Once again, the ABS code 51 is stored and this pattern is repeated for every drive cycle

Below we have the post fix capture where the ABS Pump/Modulator assembly has been replaced and the Self-test of the ABS pump motor completed
Post fix
Post fix
So, what are the conditions for the Self-test to activate?

Digging a little deeper into the exact road speed required to initiate the ABS pump motor self-test, we can refer to our “ABS signal to road speed” math channel here

The creation of the math channel requires the total number of teeth or pole count at the ABS pick up ring and the tyre diameter.

Tyre diameter can be physically measured, or, using a tyre size calculator on the web such as Tyre size calculator where the tyre diameter for this vehicle (175/65R14) is given as 0.584 meters. Alternately, if your scope is licensed for NVH, you can enter the tyre size into the “Vehicle Information” tab to reveal the tyre diameter
NVH
NVH
As for calculating the number of teeth or poles at the ABS pick up ring, using the technique described here we obtain 48-teeth. This value appears to be used often used for ABS pick-up rings!

For a really alternative use of our Keyless Entry Detector with ABS could you take a look here

The math channel therefore is written as follows:
60/48*freq(D)*(3.14 * 0.583)*60/1000*0.621371 for MPH
60/48*freq(D)*(3.14 * 0.583)*60/1000 for KMH

Below we can see the exact road speed at which the ABS self-test will be actioned (Approx. 5 KMH / 3 MPH)
Note the normal disruption to the ABS speed signal voltage during pump operation
MPH/KPH
MPH/KPH
For the ABS pump self- test to commence, from the above captures we can conclude:
1. The ABS light must be extinguished (no codes present)
2. The relevant +30, +15 and 31 terminal values to be correct (power and ground)
3. The vehicle speed to achieve 5 KMH (3 MPH)
4. No brake pedal input is required
i.e. whether the brake pedal is pressed or not, the ABS pump self-test is activated
5. ABS pump motor is run for approx. 550 ms (0.550 seconds)

I hope this information is of some help given numerous vehicles of all brands utilise this ABS self-test procedure and no doubt will adhere to a similar criterion which I am going to assume is legislated

As for the failed component with the ABS Pump/Modulator assembly, the weakest link is of course the mechanical component of the system and here we can clearly see brush wear and evidence of arcing.
Motor & Brush
Motor & Brush
Brush
Brush
With that said, the ABS pump would run seamlessly during a bench test and so the internal control of the pump motor may have failed as a direct consequence of poor brush to commutator contact. N.B. There were no visible signs of damage on the PCB assembly or attached components

Take care……Steve

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leonardorj
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Re: Abs light

Post by leonardorj »

Olá a todos, eu costumo fazer um teste mais simples. Ligo o scanner e coloco em valores reais os 4 sensorese em linha reta dentro da oficina ando com o carro e estes sensores tem que se mover juntos sem diferenças alguma e isto em linha reta.
Ele acende somente a luz do abs ou outras como Controle de Tração e ESP ?
Aqui no Brasil temos Recall feito pela VW onde estes módulos deram muito defeito. Recente a vw deu garantia num carro 2008.

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PicoKev
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Re: Abs light

Post by PicoKev »

Thanks to Google Translate!

From leonardorj:
"Hello everyone, I usually do a simpler test. I turn on the scanner and put the 4 sensors in real values in a straight line inside the workshop, I walk with the car and these sensors have to move together without any differences and this in a straight line. Does it only turn on the abs light or others like Traction Control and ESP? Here in Brazil we have Recall done by VW, where these modules were very defective. Recent vw gave warranty on a 2008 car."

Olá
My understanding is that graphing all 4 wheel speed sensors on the scan tool showed all speeds equal.
And the fault code was very specific. Fault code “51” with the description “Pump Motor in Hydraulic Modulator” (Test not successful).
I believe there were no other warning lights illuminated.

Olá
Meu entendimento é que a representação gráfica de todos os sensores de velocidade nas 4 rodas na ferramenta de varredura mostrou todas as velocidades iguais. E o código de falha era muito específico código de falha "51" com a descrição "Motor da bomba no modulador hidráulico" (teste sem êxito). Eu acredito que não havia outras luzes de aviso acesas.

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leonardorj
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Re: Luz abs

Post by leonardorj »

Ok hoje vi a foto da escova dentro do motor do ABS. Valeu ai pessoal !

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PicoKev
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Re: Abs light

Post by PicoKev »

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