2013 PACCAR MX-13 – P006C Pressure before turbo (humidity sensor) – Data erratic, intermittent, or incorrect at ignition on

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:
* when the ignition is keyed on (NO engine start), and
* ambient temperature is more than -20°C [-4°F]

Set condition of fault code

The PCI ECU (D420) detects that the measured pressure reading of the humidity sensor differs by more than 0.06 bar [0.9 psi] from the average of other pressure sensor readings on the engine for more than 5 seconds.

Reset condition of fault code

To validate the repair, key on the ignition (NO engine start) and wait for 10 seconds to allow the system to power up and the diagnostics to run.

Electrical diagram(s)

Technical data

Component & wiring check, humidity sensor (F852)
Preparation
• Key off the ignition.
• Disconnect connector F852
• Measure on the front side of wiring harness connector F852

Possible causes

Humidity sensor deviation

Additional information

* 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
* For this diagnostic, the pressure reading of the humidity sensor (F852) is compared with an average         of other engine pressure sensor readings.

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