Cummins ISB Fault code 5868, 5655, and 3151

[DNGDIESEL]

I’m working on a freightliner m2 with an Isb 6.7. I was experiencing a fault 5655 so I had the SCR sent out to be cleaned and inspected. It passed so I reinstalled it and few days later check engine light came back on with codes 5868, 5655, and 3151. When I ran the SCR system test originally it had said the SCR catalyst test was “out of range” which is why I sent it to be cleaned. While performing the SCR test after the cleaning I noticed that the Outlet NOx reading was going from 290ppm to -200 to -800 and upwards of 3000ppm. I am suspecting a faulty outlet NOx sensor. What do you think? 7 months ago I replaced the DPF filter, turbocharger, EGR cooler and valve, and had to clean the intake horn because it was clogged with soot. Also maybe 2 months ago it had the issue where the DEF tank read full but the low level light was on causing the truck to go into limp mode. A Ecm recalibration solved that issue.

 

[Deleted member 40551]

@DieselDriver

Hey there! Sounds like you've been having some trouble with your Freightliner M2. You're definitely right to suspect a faulty outlet NOx sensor based on the fluctuations you're seeing during the SCR system test. It's always a good idea to check the sensors first when dealing with emissions-related issues.

Regarding your previous repairs, it's good to know that you've recently replaced the DPF filter, turbocharger, and EGR components. These are all parts that can be prone to failure and require regular maintenance, so keeping up with them is important. Clogged intake horns can also cause major problems, so it's great that you addressed that issue before it got worse.

As for new drivers, it's important to stay on top of regular maintenance and inspection to avoid expensive repairs down the line. Oil changes, tire rotations, and regular inspections can save you a lot of money and time in the long run. It's also important to take care of yourself on long trips, staying hydrated and taking breaks as needed to avoid fatigue. Do you have any other maintenance or driving tips to share?