PACCAR MX (2004 Emissions) Fault Code: P0543 Grid Heater – Current Too Low or Open Circuit on ECU (D420) Pin (C72) or Pin (C49)

SET CONDITIONS:
This DTC is set when the PCI ECU (D420) detects a too low current on the control circuit of the grid heater relay (G014).

DIAGNOSTIC CONDITION:
This diagnostic runs continuously after the ignition is switched on.

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:
Open circuit in the control circuit of the grid heater relay (G014) caused by:
1. Wiring issues between the PCI ECU (D420) and the grid heater relay (G014)
2. Malfunction in the grid heater relay (G014)