03 December, 2025PACCAR MX (2004 Emissions) Fault Code: P1677 PCI ECU – Software Error PACCAR MX (2004 Emissions) Fault Code: P1677 PCI ECU – Software Error SET CONDITIONS:Programmed data in the ECU not correct. DIAGNOSTIC CONDITION:This diagnostic runs during start-up of the PCI ECU. RESET CONDITION:This DTC changes to inactive when the fault is no longer detected. POSSIBLE CAUSES:Software fault ADDITIONAL INFORMATION:1. The PCI ECU does not start up.2. Engine cannot be started. 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