Smart Sensors

Ask for and share advice on using the PicoScope kit to fix Heavy Duty and Off Highway machinery here
krabkakes
Newbie
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Joined: Wed Feb 03, 2021 12:22 am

Re: Smart Sensors

Post by krabkakes »

This may be a bit late but here is my $0.02.

The most common failure mode on these "smart sensors" are in-range failures. It's not very common that the CAN circuits fail, it's typically the measuring circuits. As was stated earlier, the only thing we can really measure on these is CAN - which doesn't help much.

The best diagnostics come from reviewing the data using a scan tool during real-world use. The problem with this is that it relies on a technician to have a general understanding of what a "good" range would be at any given time. The other problem with this is that we can look at a sensor and say "that data doesn't meet what I would expect" but we have no exact way to determine if the sensor is reading incorrectly or if the system is not working properly.

A perfect example of this is NH3. When DEF is injected into the exhaust stream, it bonds with the wash coat on the SCR (think of a sponge absorbing water). If the SCR was coat is damaged in any way then more NH3 will pass through to the sensor and cause high NH3 measurements. Many of these NH3 sensors are then replaced when, in all reality, it was a worn or damaged SCR wash coat.

While Ben did show a way to graph PicoScope data, you're better off using a scan tool to do the same thing (assuming you have access to one).

muttnjeff
OneWave
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Joined: Tue Jul 21, 2020 7:19 pm

Re: Smart Sensors

Post by muttnjeff »

Thanks for the post, agree with your thoughts, I find it useful to use scan data for smart sensors and if possible export the data into a spreadsheet for review.

ben.martins
Pico Staff Member
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Joined: Tue May 16, 2017 1:02 pm

Re: Smart Sensors

Post by ben.martins »

Hi krabkakes,

Never to late to add comments as it all promotes discussion which we can hopefully contribute and learn from.

I don't disagree that scan tool data is vast and when it comes to spotting the odd one out in a short space of time. Knowing what to look for is obviously key as you say, and many OEM's can now provide you a list of the expected values in their technical information. Scan tools give you lots of data very quickly and as such will always be a part of the diagnosis - where you have a scan tool available to you.

An example of where the scan tool isn't always clear to a technician is when Gateway ECU's are used. I was assisting a customer a few months ago where the scan tool was reporting the After Treatment ECU was off line as was all the NH3 sensors. With no data available to report the sensor readings the technician did the next thing which was to check powers, grounds, CAN bus resistance at the after treatment ECU and at the NH3 sensors and everything was checking out as OK. Everything at that moment was pointing towards to the After treatment ECU as the scan tool had said but, as we all get a little twitchy about replacing an ECU, they got in touch and we walked through the issues. We then got a capture of the CAN network at the After treatment ECU and using the techniques mentioned in this post, could determine that the after treatment ECU was online and sending out data and we could also see that data relating to the NH3 sensors.

The issue wasn't with the After treatment ECU but on this machine the Engine ECU acted as a gateway. As the DLC was on another branch where the only access to the After treatment ECU was through the Engine ECU, we concluded that actually the Engine ECU was at fault. It was replaced and the scan tool could now see the missing after treatment ECU again.

Every tool has it's place in the diagnostic challenges we face. What makes a good technician isn't the amount of tools they have but knowing when to use the right tool for the right job.

krabkakes
Newbie
Posts: 2
Joined: Wed Feb 03, 2021 12:22 am

Re: Smart Sensors

Post by krabkakes »

ben.martins wrote:
Wed Feb 17, 2021 4:06 pm
An example of where the scan tool isn't always clear to a technician is when Gateway ECU's are used.
Absolutely! That is a great use of a PicoScope for CAN decoding! In the trucking industry we're seeing more and more gateway modules as the industry continues to focus on reliability (isolating critical networks from customer-installed devices, or non-critical devices like the radio) and data security.

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