PACCAR MX (2004 Emissions) Fault Code: U1879 CAN Communication – Message (A1SCREGT) Out of Range, Exhaust Gas Temperature before SCR Catalyst from Aftertreatment System

PACCAR MX (2004 Emissions) Fault Code: U1879 CAN Communication – Message (A1SCREGT) Out of Range, Exhaust Gas Temperature before SCR Catalyst from Aftertreatment System

SET CONDITIONS:
This DTC is set when a CAN message is received correctly, but the content (signal value or status) is out of the expected range.

DIAGNOSTIC CONDITION:
The diagnostic runs continuously when the ignition is keyed on or when the engine is running.

CORRESPONDING OBD READINESS MONITOR:
None

RESET CONDITION:
The DTC changes to inactive after the diagnostic runs and passes.

REPAIR VERIFICATION:
1. Clear all DTCs.
2. Test drive or operate the vehicle to meet the diagnostic conditions and set conditions.
3. Did the DTC come back?
– No, repair successful
– Yes, repair unsuccessful

POSSIBLE CAUSES:
1. A corrupt or empty CAN message
2. A malfunction in the system from which the message originates

ADDITIONAL INFORMATION:
1. A ‘message out of range’ DTC is activated by the receiving ECU but indicates a malfunction within another system which communicates with this ECU.
2. The cause of the DTC must be sought in the system from which it originates.

Example:
1. [ECU 1] detects an incorrect or missing signal from [sensor A].
2. [ECU 1] sets [DTC 1] (In this specific case, an open circuit DTC).
3. [ECU 1] constantly informs [ECU 2] about the status of [sensor A] via CAN messages.
4. Since the data received from the sensor is not available or not plausible, an ’empty’ CAN message is sent from [ECU 1] to [ECU 2].
5. [ECU 2] interprets the empty message as being out of the expected range and sets the ‘out of range DTC’ [DTC 2].