03 December, 2025PACCAR MX (2004 Emissions) Fault Code: P1518 Aftertreatment System – Engine Torque Derate Active PACCAR MX (2004 Emissions) Fault Code: P1518 Aftertreatment System – Engine Torque Derate Active SET CONDITIONS:This DTC becomes active if the DTC from which it originates activates an engine torque derate. RESET CONDITION:This DTC becomes inactive as soon as the DTC from which it originates has become inactive. ADDITIONAL INFORMATION:IMPORTANT: Do not troubleshoot this DTC since it originates from another active DTC. This DTC only indicates that an engine torque derate is active. 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