PACCAR MX (2004 Emissions) Fault Code: P0493 Fan Speed Control – Incorrect

PACCAR MX (2004 Emissions) Fault Code: P0493 Fan Speed Control – Incorrect

SET CONDITIONS:
The PCI ECU (D420) detects that the actual fan speed is higher than expected.

DIAGNOSTIC CONDITION:
This diagnostic runs every 300 seconds:
1. When the engine has been running for more than 300 seconds
2. When the engine speed is greater than 1000 rpm
3. When the coolant temperature is above 70°C [158°F]

CORRESPONDING OBD READINESS MONITOR:
None

RESET CONDITION:
This DTC changes to inactive when the fault is no longer detected.

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:
Faulty electronically controlled fan clutch

ADDITIONAL INFORMATION:
1. The negative side coil of the electronically controlled fan clutch (B335) is controlled with the duty cycle by the PCI ECU. When the duty cycle is:
– High, the fan speed is low or decreasing
– Low, the fan speed is high or increasing
2. The fan speed is monitored by the fan clutch internal speed sensor.