Hall effect sensor signal question

Steven Mechanic Spokane, Washington Posted   Latest   Edited   Bounty  
Bounty
Electrical
1998 Mercedes-Benz S320 LWB 3.2L 5-spd (722.6)
P0341 - Camshaft Position Sensor "A" Circuit Range/Performance Bank 1 or Single Sensor

Who's up for an ASE type of question about hall effect sensor signals?

The above listed vehicle has fault code P0341 Camshaft Sensor Signal Range/Performance. The technician verifies that there is no problem with the electrical circuits for the sensor. A new OEM camshaft sensor is installed, yet the fault code still comes back after the engine runs for just a few seconds. The technician captures the hall effect signal for the camshaft sensor on an oscilloscope. The red trace in the attached picture is the bad signal.

Tech A says the sensor is too close to the trigger wheel.

Tech B says the sensor is too far away from the trigger wheel.

Which tech is correct, and can you explain why? Bounty goes to the best explanation!

Update:

To be clear, either Tech A or Tech B is correct. No need to consider other possible answers. Also, the year/make/model/engine was given if anyone needs to look up how the system works, but I'll give a little help for those not able to look it up.

The trigger wheel is just a short metal tab that passes by the sensor tip. The signal voltage is at 12 volts for the majority of rotation until the metal tab passes by the sensor tip, at which point the signal voltage drops to 0 volts for a short amount of time until the metal tab has moved past it and the voltage returns to it's normal "at rest" 12 volts. In the image the bad signal drops to 0 volts at the correct time, but doesn't stay at 0 volts for long enough.

Another Update:

Some members are mentioning that if the pulse width were to get wider, then it should get wider in both directions. In other words, the point at which is drops to 0 volts would have to change along with where it returns to 12 volts. In response to that, I will post pictures of the actual captures that were taken . I don't think we need the scope file, but if someone wants the scope file, I can grab it on Monday when I return to work. Here's the pictures: Bad CMP signal and Good CMP signal.

+4
Hans Technician
Salt Lake City, Utah
Hans Default
 

I’d say technician B. it seems sort of like a goalie cutting down the angle by moving further away from the net. The further away, the smaller the area of goal potential. The closer the goalie is, the greater the goal potential, because the net is significantly more open relative to the goalie.

+2 Default Ð2 Bounty Awarded
Agree
Mike Diagnostician
Toronto, Ontario
Mike Default
 

I agree with Hans on this one Tech B. When the trigger wheel 'tooth' is in close enough proximity to the sensor tip the reference voltage supplied by the ECM will be pulled low. If the gap is excessive it may not be close enough to the trigger wheel to pull it low for the entire duration. Not sure of the particular design but I would also make sure the axial runout of the sensor wheel is…

0 Default Ð2 Bounty Awarded
Mervin Owner/Technician
Harlan, Indiana
Mervin Default
 

Hello, I would think Tech B, Because in my mind if the trigger wheel (metal) is too far away the magnetic pull is pulled down too late and let go of too soon, thus you would have a much shorter pull down in the signal. Tech A (wrong) If too close to the sensor , the magnetic pull is pulled down too soon and let go of too late , thus you would have a much longer pull Down in the…

0 Default Ð2 Bounty Awarded
Paul Technician
Sarasota, Florida
Paul Default
 

The camshaft key only has one chance to get picked up by the magnetic field of the cam sensor per revolution. The further away it is from the field, the less opportunity it will have to be in the magnetic field, and the closer it is the longer it will be in the magnetic field. So I say tech B is right.

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Victor Owner/Technician
Doral, Florida
Victor Default
 

Tech A is correct.

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Rick Technical Support Specialist
Saint Charles, Missouri
Rick Default
 

I'm going with b and hans' explanation but we will need to take away the goalies stick to get the sam performance results. LOL

0 Default Ð2 Bounty Awarded
Michael Mobile Technician
Clinton, Utah
Michael Default
   

Wow Steven, These should just work right? Being a hall effect sensor I would think that too close is the issue. Going to go with "A". The sensor could pick up the walls of each tooth and shorten the window. Looking forward to the correct answer.

0 Default Ð2 Bounty Awarded
Dave Mobile Technician
Ironton, Ohio
Dave Default
 

I I am going with tech A. I think that the closer to the wheel the sooner the signal would get triggered.

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Sadel Owner/Technician
Fairfield, Ohio
Sadel Default
 

I'm going to go out on a limb here and say, neither. I would say that multiple sensors are just "drawing" what the trigger wheel is giving it. Being that there was 2 different engine managements for that engine, and HFM and an ME, id say that the incorrect engine is installed. Being the vehicle is a 98 it should have the ME style set up which is supposed to be a "wider" trigger segment which…

+4 Default Ð2 Bounty Awarded
Agree
Nathaniel Diagnostician
Ashton, Ontario
Nathaniel Default
 

Now that's interesting. Those tabs are not clocked the same. The low pulse would be both shorter and later. We would need an actual scope grab to see if that were the case, though.

0 Default Ð2 Bounty Awarded
Steven Mechanic
Spokane, Washington
Steven Default
 

That's a great idea, and one that was considered at the time of this diagnosis. However, that did not turn out to be the issue. Thank you Sadel for adding this information.

+2 Default Ð2 Bounty Awarded
Chris Technical Support Specialist
Commack, New York
Chris Default
 

I'm going to go with Tech A. I could be completely off base but here is my rational. The Wave form is high(5v?) to low (0v?), not low to high. That would make the trigger a notch or a window. With the sensor closer there would be less off time due to the distance from the edge of the window being slightly closer than expected. If it were a tooth used to trigger the closer sensor would create a…

0 Default Ð2 Bounty Awarded
Chris Technical Support Specialist
Commack, New York
Chris Default
   

Thanks for the Description and operation update.

0 Default Ð2 Bounty Awarded
Nathaniel Diagnostician
Ashton, Ontario
Nathaniel Default
 

Steven, That image shows the red trace being triggered in time with the known good CMP signal. Are you sure this was the case? Air gap can certainly affect Hall effect duration, but it should have the same middle point. The leading and trailing edges should be what move.

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Allan Instructor
Winnipeg, Manitoba
Allan Default
   

Steve shouldn’t ASE type questions have 4 options? I would choose D. If the sensor were too close to the reluctor I would expect it to turn on sooner and off later, if the sensor were too far away i would expect it to turn on later and off sooner, as Mervin stated. In your example the signal turns on at the same time as the “good” example but turns off early. If the air gap were too large and…

+1 Default Ð2 Bounty Awarded
Hans Technician
Salt Lake City, Utah
Hans Default
 

However keeping with true ASE tests, "pick the most correct answer" comes into play, and he only gave us two answers to choose from!

+1 Default Ð2 Bounty Awarded
David Owner/Technician
Sierra Vista, Arizona
David Default
 

Steve, you did a good job replicating a ASE question, short and vague. I would say answer D ( neither) as a sensor too close would have a trace that starts later and ends sooner. A sensor too far away would start sooner and end later. With the signal starting at the same time and ending early is more like a reluctor or window issue. This image reminds me of a bent reluctor on a Chrysler flywheel.

0 Default Ð2 Bounty Awarded
Steven Mechanic
Spokane, Washington
Steven Default
 

Yes, ASE questions can be frustrating! There are so many other things that come to mind when you are trying to figure out the correct answer, but at least there are only two options to chose from in this case, so you have a 50/50 shot at getting it right. Besides choosing between Tech A or Tech B, there is also a bounty for the best explanation. I'm hoping for some technical details as to why it…

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Brian Diagnostician
Seneca, South Carolina
Brian Default
 

I going with neither. Looks like the wrong tone ring (tone ring / trigger wheel is to narrow) on the cam gear.

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Walter Mobile Technician
Plantation, Florida
Walter Default
 

IMO Tech B is correct, the sensor gap is to much or the sensor has a weak magnet. The sensor is picking up the change in the magnetic field than quickly loosing it due to the reason given.

0 Default Ð2 Bounty Awarded
Dmitriy Analyst
Toronto, Ontario
Dmitriy Resolution
 

In Honeywell’s guide to Hall Effect Sensing and Applications we can find the following: diag​.​net/file/f5eatj5ej… ​ This sounds like what you are experiencing. But what is that mysterious “capacitive coupling“? Well, a car of this vintage probably uses a single element Hall effect sensor with basic circuitry inside it, like this: diag​.​net/file/f406ury4j… ​ The…

+6 Resolution Ð2 Bounty Awarded
Helpful
Roland Technician
Plainfield, Illinois
Roland Default
 

Tech B is right

0 Default Ð2 Bounty Awarded
Steven Mechanic
Spokane, Washington
Steven Resolution
 

The correct answer is Tech A. The sensor is too close to the trigger wheel. The air gap for the CMP sensor on this car is adjustable. There was no shim installed. The techs shimmed the sensor to move it further away in order to get the proper signal. As for answering why the sensor signal reacts the way it does, I think Dmitriy Levchenkov had the best explanation, and I have awarded him the…

+2 Resolution Ð2 Bounty Awarded
Hans Technician
Salt Lake City, Utah
Hans Default
 

Learn something new every day! I just guessed and made stuff up :D

0 Default Ð2 Bounty Awarded