# P21C4 on the 2023 Ram 3500

The bulletins listed name this code in NHTSA's summary, or are about the same components. A bulletin or a recall listed here may apply to the model year. None of it is a diagnosis.

Nobody has written a description of this code yet.

## Bulletins for this model year that name P21C4

- [11018649](https://open.wenmarpro.com/bulletins/11018649), 2025-05-29: Module, Urea Pump/Level: HD 6.7L \(ETL/ETN/ETM\) with Mil On P21C4\-00 \(Reductant Line Heater Relay Control Circuit High / U11C1\-00 \(Reductant Control Module Received Implausible Data From ECM/PCM\), do not replace the DEF Pump. Follow TSB's released and appropriate Service Diagnostics.
- [11016060](https://open.wenmarpro.com/bulletins/11016060), 2025-03-28: "6 CONTROL UNIT, Diesel Exhaust Customer complaints with malfunction light illuminated on 2019 thru 2024 MY DJ / D2 / DD / DP vehicles with 6.7L \(ETL / ETM / ETN\) built on or before October 15,2024 and exhibiting DTCs P21C4\-00 \(Reductant Line Heater Relay Control Circuit High\) and / or U11C1\-00 \(Reductant Control Module received implausible Data from ECM / PCM\). These DTCs will occur after installation of service DCU 68458603AB. Do not replace parts until after the TSB 25\-008\-24 is performed. If the DTC\(s\) continue to set, then follow the Service Diagnostics for the applicable DTC."
- [11015599](https://open.wenmarpro.com/bulletins/11015599), 2025-03-13: Malfunction Indicator Lamp \(MIL\) Illumination, Diagnostic Trouble Codes \(DTCs\) P21C4 – \(Diesel Exhaust Fluid\) Reductant Line Heater Control Circuit High, and U11C1 – Reductant Control Module Received Implausible Data From ECM/PCM, Set
- [11010636](https://open.wenmarpro.com/bulletins/11010636), 2024-11-18: "Flash: Diesel Exhaust Fluid \(DEF\) Dosing Control Unit \(DCU\) Update Customers must experience a Malfunction Indicator Lamp \(MIL\) illumination and the vehicle must exhibit/set the following Diagnostic Trouble Code \(DTC\): ● P21C4\-00 \- Reductant Line Heater Relay Control Circuit High. ● U11C1\-00 \- Reductant Control Module Received Implausible Data From ECM/PCM. These DTCs will occur after installation of service DCU 68458603AB. This bulletin involves reprogramming the DCU with the latest available software."