2017 FCCC XCA Unknown Or Other Problems

The after treatment emission system DEF sensors failed. The failed part may be available from Freightliner, but it was under warranty and I they retained the failed part. (Freightliner part # 04-31353-003.) Note: the DEF after treatment system was functioning properly, but sensors monitoring tank level, temperature, and quality failed, sending false info to the ECM that the DEF level was low/empty and quality was out of range/poor. This results in an engine derate that leaves the vehicle unable to go above 5 mph. The safety issue is from a mandatory engine derate that leaves the driver only able to reach 5 mph. On an interstate highway with nowhere to pull off, this puts the occupants of the vehicle and other vehicles on the road in danger. This problem has been reproduced by the manufacturer, Freightliner. The "DEF head(er)" unit has proven to have a high failure rate and replacement...