The following was written by Michael Eilbracht on Diagnostic Network.
Here is a case study I have using scan data and some basic circuit checks with a Dvom. It has Active Fault Codes 3868, 4677, 4572. These codes state basically that it has issues with the diesel exhaust fluid quality, temperature, and level. All of these codes say it has an abnormal update rate.
So what does the Cummins ECM mean by abnormal update rate? A computer has to able to take in information and be able to understand the information it’s getting. What Abnormal Update Rate means in this scenario, is the computer is seeing information that is not making any sense, so the computer logs the codes. The computer is not seeing the proper information from the DEF Tank Level/ Temperature/Quality Sensor. All of these sensors are one unit that are installed inside the DEF Tank. So we have the codes, where should we start? First thing I always do is check freeze frame.
So for the quality code nothing looks to bad here so far, temperature and level looked ok at first glance. Here is the rest of the freeze frame for this code.
So for the Freeze Frame on the 3868 code their is really nothing that is showing anything useful for diagnosing this code. Here is the Freeze Frame for the 4677 Code.
So for the last code it turned up short as well. Freeze frame showed nothing conclusive. I have seen this happen before where freeze frame will not help you at all. Also pay attention to the PIDs that are in freeze frame. Sometimes Cummins will leave out important PIDs in the freeze frame. So after seeing nothing in freeze frame I decided to see if I saw anything in regular numerical data. In the first one I see nothing useful.
After scrolling down, I finally find some useful information. I find that my Diesel Exhaust Fluid Quality Temperature says it is 32 degrees fahrenheit, the quality percent is zero, the tank level is 8 percent, and I can see that in the tank it is full of DEF. The tank temperature says it’s at 68 degrees fahrenheit. My tank temperature sensor voltage is also at zero volts. Interesting, my tank temp says 68 degrees fahrenheit but my tank temperature sensor voltage says zero volts. What has happened is Cummins has put in a substituted value during this default. From my experience Cummins will not default the voltage values, so pay attention to the voltage values on your PIDs. As everyone has seen before in a prior case study, I have been using the Texa unit and I am very impressed with the capabilities of this tool. Here I will show all the screen shots I have for the Texa. The Texa gave me the same codes as Insite and gave me the same data.
Hooking up to the Texa
On the Texa 4 link I was looking at the coolant temperature PID to see if it matched close to the DEF tank temperature. However, after I saw the signal voltage for tank temperature was not correct, I now knew to ignore the DEF tank temperature PID. This is also shown in the next Texa capture. Also, as you can see, the Texa is showing the same amount of tank level for DEF fluid.
So now that I have shown all this, what should you check to find the issue? Since everything that is effected is inside the DEF tank, you need to check powers, grounds, and communication lines. First thing I did was check power and ground to the unit, and it held voltage when I loaded the circuit.
Ok so after I saw this reading, I ruled out a open circuit or short to ground. The next step was to load the circuit and see if I had any connection issues.
As you can see, the voltage dropped a little bit, but that is expected. This indicates the circuit can carry a load. After that, I checked Can Hi and Can Lo. Can Hi and Lo checked out ok. So after that, I decided to do some harness shakes and pulls to just make sure. I used the data logger on Texa to log the data while I shook the harness, that way if I did miss something on the screen while I was shaking the harness it would catch it.
I saw nothing obvious on the data logger. I have now finished the diagnosis, it needs a new DEF tank level sensor and quality sensor assembly. Replacing this sensor is no easy task on this bus. So to prove I fixed the issue I just plugged in a good sensor assy and it gave me these codes on the Texa.
As you can see the tank level code, quality sensor code, and the tank temperature code went yellow on Texa which means the codes are now inactive and the sensor assembly is communicating with the Cummins ECM. Diesel exhaust fluid quality abnormal rate of change is active because their is no DEF in the tank.
Well that is it, hope everyone enjoyed it. Sorry I didn’t go hi tech this time with the Pico, due to the nature of the symptoms I didn’t think the Pico was needed. That’s pretty shocking coming from me right? Lol. Hope everyone has a good evening. Stay tuned, I have more to share.
About the Author
Michael Eilbracht is a full time transit bus tech, with 21 years experience in electrical and driveability diagnostics. He also runs a training and mobile diagnostics business MJE diagnostics. He also specializes in ocsilliscope training for heavy duty applications, and he is the distributor for the Midwest for Autonerdz.com. Micheal and Autonerdz sell pico scopes for the automotive, HD, and marine industries. He is also a ASE certified master transit bus tech with a L2 advanced level certification. His website is mjediagnostics.com.