PACCAR MX (2004 Emissions) Fault Code: P0640 Grid Heater Relay – Voltage Too High or Short Circuit to Supply on ECU (D420) Pin (C55)

PACCAR MX (2004 Emissions) Fault Code: P0640 Grid Heater Relay – Voltage Too High or Short Circuit to Supply on ECU (D420) Pin (C55)

SET CONDITIONS:
This DTC is set when the ECU detects a higher voltage than expected on pin C55.

DIAGNOSTIC CONDITION:
The diagnostic runs continuously when the ignition is keyed 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:
1. The sensor or actuator signal wiring has a short circuit to supply.
2. A malfunction of the sensor or actuator

ADDITIONAL INFORMATION:
Through pin C55, the PCI ECU determines the status of the grid heater relay.