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Service bulletins for the 2023 Ram 4500

A bulletin is a manufacturer's communication to its dealers, as NHTSA indexes it. The summary is NHTSA's. The document is the manufacturer's: read it at NHTSA. A bulletin is not a recall, and listing a model year does not mean every vehicle of it is concerned.

294 on file from NHTSA, as of 2026-10-19.

About P21C4 on the 2023 Ram 4500: what the code means, and the bulletins and recalls about the same components.

By type

By component

By trouble code

Only bulletins with trouble code: P21C4 are shown. Show all

Bulletins, newest first
91005982025-05-29. Service bulletin. ENGINE; UNKNOWN OR OTHER. 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.
91005082025-03-28. Service bulletin. UNKNOWN OR OTHER. "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."
S1625000002 REV.B2025-03-13. Service bulletin. UNKNOWN OR OTHER. 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
25-008-242024-11-18. Service bulletin. UNKNOWN OR OTHER. "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."

The summaries are NHTSA's. Each bulletin's page links NHTSA's copy of the manufacturer's document.