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Volvo All Engines (2004 Emissions) Fault Code: PID 172 FMI 4 Intake Air and Humidity Sensor

Fault Condition: The Electronic Malfunction Lamp (EML) will turn on and PID 172 will set when the Engine Management System (EMS) Module senses that the Intake Air Temperature Sensor signal voltage is less than 0.5 volts or greater than 4.9 volts for 1 second. If the Intake Air Temperature Sensor voltage returns to between 0.5 volts and 4.9 volts for more than 1 second, the fault will become inactive.

Possible repairs:

Turn the ignition key OFF first.

1) Disconnect the Intake Air Temperature and Humidity (IATH) Sensor connector. Measure the resistance between pins 3 and 4 of the Intake Air Temperature and Humidity (IATH) Sensor with the ambient air temperature between 32° and 104°F (0° and 40°C) If the measured resistance is NOT between 30029 and 5575 ohms, replace the sensor.
2) Disconnect the Intake Air Temperature and Humidity (IATH) Sensor connector. If continuity exists on any pin, replace the Intake Air Temperature and Humidity (IATH) Sensor.
3) Disconnect the Intake Air Temperature and Humidity (IATH) Sensor harness connector. Measure the resistance between pins 3 and 4 of the Intake Air Temperature and Humidity (IATH) Sensor with the ambient air temperature between 32° and 104°F (0° and 40°C). If the measured resistance is NOT between 30029 and 5575 ohms, replace the Intake Air Temperature and Humidity (IATH) Sensor.
4) Connect the Intake Air Temperature and Humidity (IATH) Sensor harness connector. Connect connectors to the Engine Management System (EMS) Module. Turn the ignition key ON. If PID 172 is still active, check the Engine
Management System (EMS) Module and connector A for dirt, loose or shorted pins, or any other repairable damage. If no problems are evident or are not repairable, replace the Engine Management System (EMS) Module
and retest the system. If PID 172 is NOT active, the diagnostic procedures have corrected the problem. Check all connectors to ensure proper connections.
5) Disconnect the Intake Air Temperature and Humidity (IATH) Sensor harness connector. Disconnect Engine Management System (EMS) Module harness connectors A and B. Check for continuity between Engine
Management System (EMS) Module harness connector A pin 43 and all other pins on Engine Management System (EMS) Module connectors A and B. If continuity exists, the signal line is shorted to one of the other Engine Management System (EMS) Module circuits. Locate and repair the short circuit to voltage, then replace the sensor. If there is NO continuity, the signal line is shorted to voltage somewhere else in the harness. Locate and repair the short circuit to voltage, then replace the sensor.
6) Connect the Intake Air Temperature and Humidity (IATH) Sensor harness connector. Connect connector A to the Engine Management System (EMS) Module. Turn the ignition key ON. If PID 172 is still active, check the Engine
Management System (EMS) Module and connectors A, and B for dirt, loose or shorted pins, or any other repairable damage. If no problems are evident or are not repairable, replace the Engine Management System (EMS) Module and retest the system. If PID 172 is NOT active, the diagnostic procedures have corrected the problem. Check all connectors to ensure proper connections.