1606 Def Quality Sensor issues
Greetings everyone. I have another case study to share. And yes I have posted a case study before about a similar issue but on this particular case study I have stumbled upon something that I think will be beneficial for everyone that uses scopes in diagnostics and I hope that the other HD Techs on here will take notice and share this with other Techs who think they don't need a scope. This case study is on a 2016 New Flyer Transit Bus with a Cummins 6.7. It has codes 4868, 4677, 4572, 1669,6613,4739, 1715. All of these codes point towards the Def Quality Level and Temp Sensor. This Sensor has a Power, Ground, and Can Hi and Lo connections. So all information about Quality, Level, and Temp are transmitted across the J1939 Network. So for these codes the first thing I do is look at freeze frame for when the codes set. As you can see by the freeze frame pics below for each code the only real indicator of an issue is the tank level. If you look at the codes and freeze frame at the bottom from left to right you will see this. The temperature does change but nothing that would raise an eyebrow. So after seeing this data the only way to confirm if this is a bad Def Quality and Level Temperature Sensor is to test the Sensor with a scope. To check this sensor I am going to hook up to Power and Ground of the Sensor and then look at Can Hi and Lo of the sensor. I will also hook up a current clamp so I can synch the Can messages to the Def Quality level and Temp Sensor. After making my hookups I test the sensor by doing a key on engine off test. I have found from experience that these Computer Controls from Cummins put more current into the system on a self check during key on than during a regular automated test for different components. So what I pay attention to is the current of the sensor on key on and then the can messages. On the first capture I have with the Escope Elite I see a sudden drop in Battery Voltage and then a rise in the Def Quality Level and Temp Sensor Current. Current is the yellow trace. Red is Voltage and Green and Blue is Can Hi and Can Lo. As you can see right away the drop in Voltage makes the current of the sensor go up momentarily. And you can also see by the next scope capture that the rise in Current is effecting the Can Hi and Lo signals for the sensor. Then if you look at the key on current it is actually low. A known good one will pull 2.5 amps on key on. Plus another thing to note from the first capture is all the drops in voltage at the end as well. All the Voltage Drops line up with the Def Sensor Current. So after seeing this info I have condemned the Def Sensor for being faulty. To prove my point I plugged in a brand new one and did another capture and I got 2.5 Amps on key on engine off. Plus I saw no more interference in the can. The momentary drop in Voltage that is on the new Sensor capture is because of other Aftertreatment components drawing current on that system. I did not have a current clamp on the other components to confirm what this drop was but normally during engine warmup these drops in Voltage are because of the Nox Sensor Heaters. A new sensor fixed this issue. The Bus has run for a month with no issues. The scope really helped confirm the problem was the sensor. Without the scope you would not be able to see the koeo current of the sensor or the changes in current over time. Without a scope you can not be 100 percent sure if a new sensor will fix your issue. I hope everyone enjoyed that. Have a good evening.
Good-stuff, Mike. It’s great to see the approach on the HD side of the industry. Youse guys have as much electronic control now as we do. The other tech had better get on-board. If not, both you and Brent Delfel are going to have your hands full 😎
Excellent case study Mike. Thanks for your input on items such as this. Very interesting to see the correlation between the drop in system voltage and the can network.
Thanks. The newer Cummins Can Systems are different as in backbone resistance with all the modules plugged in. So you will not see 60 ohms, it will be lower and Cummins puts a range in it which makes it time consuming to troubleshoot because to really verify backbone integrity you have to unplug all the modules. Chacking Can with a Scope on these systems is much faster.
Very nice write up, good to see guys in the heavy duty market using scopes.