Fault code information
2 trip MIL
3 drive cycle recovery
Readiness group – None
Freeze frame type – Comprehensive
Description of component(s)
The humidity sensor is a smart sensor that communicates with the PCI ECU via E-CAN.
The sensor measures the following three properties of the drawn in precompressor (VTG turbo charger) air in the inlet air pipe:
* Relative humidity
* Pressure
* Temperature
Relative humidity
The relative humidity refers to the moisture content percentage of the air compared
with the saturated moisture level at the same temperature and pressure.
Effect on the system:
* Determines NOx emissions
Higher measured relative humidity results in a lower calculated NOx emission.
Precompressor temperature
Effect on the system:
* Determines soot emissions
Higher measured precompressor temperature results in lower calculated soot formation in the engine.
* Calculates exhaust gas pressure before the turbine;
Higher measured precompressor temperature results in lower calculated exhaust gas pressure before the turbine.
* Limits the maximum engine torque; for example, to limit the cylinder pressures during cold ambient conditions or driving at high altitudes.
* Determines turbocharger compressor flow and thus the detection of VTG surge
Surge can typically occur at high compressor pressure ratios and low compressor mass flows.
* Calculates the temperature after the turbocharger compressor
Higher measured precompressor temperature results in higher calculated temperature after the turbocharger compressor.
Precompressor pressure
Effect on the system:
* Corrects pressure before turbine
Higher measured precompressor pressure results in higher calculated exhaust gas pressure before the turbine.
* Determines soot emissions
Higher measured precompressor pressure results in lower calculated soot formation in the engine.
* Calculates the temperature after the turbocharger compressor
Lower measured precompressor pressure results in higher calculated temperature after the turbocharger compressor.
* Limits the maximum engine torque when driving at high altitudes (low air density)
Lower measured precompressor pressure results in higher engine torque reduction.
* Detects VTG surge, the sensor is used to determine the compressor pressure ratio; surge can typically occur at high compressor pressure ratios and low compressor mass flows.
Location of component(s)
Diagnostic condition
This diagnostic runs:
* 300 seconds after an engine start, and;
* when the engine is running at a steady load, and;
* vehicle speed is above 35 km/h [22 mph], and;
Set condition of fault code
The PCI ECU (D420) detects that the measured ambient temperature differs too much from the calculated ambient temperature for more than 300 seconds.
Reset condition of fault code
This DTC changes to inactive when the fault is no longer detected. To validate the repair, drive the vehicle until the coolant temperature is at least 70°C [158°F]. Once the minimum target temperature has been reached, proceed at a minimum speed of 80 km/h [50 mph] in the highest gear possible with the engine speed between 1100 and 1500 rpm and set the cruise control. This test is best performed with a loaded vehicle/trailer, but if load is unavailable, turn as many engine power consumers on to produce engine load. Perform this test for roughly 5 to 8 km [3 to 5 miles] or in 3 separate 1.5 km [1 mile] increments if a steady 5 to 8 km [3 to 5 miles] is unachievable. Use a flat road, if possible.
Electrical diagram(s)
Technical data
Possible causes
* Ambient temperature sensor deviation
* Humidity sensor deviation
Additional information
* The measured ambient temperature is compared with the calculated ambient temperature.
* The ambient temperature is calculated by the PCI ECU. Other involved sensors and input signals used to calculate the ambient temperature are the precompressor temperature (humidity sensor (F852)), engine cooling fan state (on or off), vehicle speed, and fuel injection quantity.
