PACCAR MX (2004 Emissions) Fault Code: P1874 Temperature Before Turbocharger Compressor (Humidity Sensor) – Data Valid but Too High

PACCAR MX (2004 Emissions) Fault Code: P1874 Temperature Before Turbocharger Compressor (Humidity Sensor) – Data Valid but Too High

SET CONDITIONS:
The PCI detects that the temperature before compressor measured by the humidity sensor is higher than expected.

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

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? (Can be pending, inactive or active)
– No, repair successful
– Yes, repair unsuccessful

POSSIBLE CAUSES:
1. An engine starts shortly after a hot engine shut-down
2. Malfunction of the humidity sensor

ADDITIONAL INFORMATION:
1. The humidity sensor (F852) is a smart sensor that communicates with the PCI ECU via E-CAN.
2. The sensor measures the following three properties of the air in the inlet air pipe (before the turbocharger compressor):
– Air temperature
– Air pressure
– Relative humidity

IMPORTANT: The temperature in the inlet pipe can rise significantly when a hot engine is shut-down at high ambient temperatures. When the engine is restarted shortly after the hot engine shut-down, the temperature in the inlet pipe can briefly exceed the threshold, resulting in this DTC. Check DTC freeze frame data parameter ‘Engine running time since ignition on’. If the DTC was activated shortly after a hot shutdown, no repair is needed.