03 December, 2025PACCAR MX (2004 Emissions) Fault Code: P109C Common Rail Pressure Release Valve – Current Too Low or Open Circuit on ECU (D420) Pin (C4) PACCAR MX (2004 Emissions) Fault Code: P109C Common Rail Pressure Release Valve – Current Too Low or Open Circuit on ECU (D420) Pin (C4) POSSIBLE CAUSES:No repairs are necessary. ADDITIONAL INFORMATION:Do not troubleshoot this DTC. Share on Facebook Opens in a new window. Tweet on Twitter Opens in a new window. Pin on Pinterest Opens in a new window. Back to blog