Fuel trim is the action the PCMtakes to achieve the correct air/fuel mixture which allows the engine to operate normally. When the engine load increases, the O2 Sensor number 2 constantly prompts the PCM to make adjustments to the mixture for maximum engine efficiency.
The diagnostic code P0173 OBDII is set when the PCM (Powertrain Control Module) cannot maintain the stoichiometric air/fuel mixture. You may receive a fuel leveling request from the post-catalytic Oxygen (O2) Sensor, and that request exceeds the ability of the PCM to configure the fuel setting to meet the required setting level for a while.
Once the engine is on, it can be unexpectedly turned off.
Causes of OBD2 P0173 Generic
The reasons for setting the error code P0173 OBD2 are
Vacuum leakage is likely.
There may be engine oil in the fuel.
Oxygen Sensor #2 may be defective.
There may be oil in the MAF sensor
MAF sensor is defective.
Damaged fuel pressure regulator.
Possible solutions of the DTC code P0173 Generic
When solving the problems caused by the DTC code P0173 OBDII, you should take into account the following:
With a scanning tool, look at the MAF Sensor reading in grams/sec. Check with the manufacturer's data for recommended values. Change it if they are not within those parameters.
Disconnect the Mass Airflow (MAF) Sensor and check for oil. If not, check the fuel pressure and note that the regulator should not leak. Make sure none of the hoses are damaged or disconnected. Repair if necessary.
Check the intake manifold connections for vacuum leaks or defective air supply hose.
Inspect O2 Sensor connectors for oil intrusion. Repair oil leaks and replace contaminated Oxygen Sensor.