P CODES (POWERTRAIN) P0100 - P0199 P0173

    Comprehensive Guide to Diagnose and Repair P0173 Code: Fuel Trim Malfunction (Bank 2) Explained

    Definition of P0173 - Fuel Trim Malfunction (Bank 2)

    The trouble code P0173 is triggered when the Engine Control Module (ECM) detects an issue with the fuel trim on Bank 2 of the engine. Fuel trim is the process by which the ECM adjusts the fuel mixture to maintain an optimal air-fuel ratio. A malfunction may lead to reduced fuel efficiency, poor engine performance, and increased emissions. Bank 2 refers to the side of the engine with the second set of cylinders, typically in V-type and horizontally opposed engines.

    How to Diagnose P0173

    Before starting the diagnostic process, gather the necessary tools such as a diagnostic scanner, multimeter, and fuel pressure gauge. Follow the steps below to diagnose the P0173 code:

    Step 1: Check for related codes. Use the diagnostic scanner to read any other trouble codes stored in the ECM. If other codes are present, diagnose and repair those issues first, as they may be causing the P0173 code.

    Step 2: Inspect for vacuum leaks. A vacuum leak can cause a lean condition and trigger the P0173 code. Carefully inspect all vacuum lines, hoses, and intake gaskets for any signs of damage, cracks, or loose connections.

    Step 3: Test the Mass Air Flow (MAF) sensor. The MAF sensor measures the amount of air entering the engine, which helps the ECM calculate the appropriate fuel mixture. Use a multimeter to test the MAF sensor's voltage and resistance to ensure it's functioning correctly. If it's faulty, replace the sensor.

    Step 4: Check the Oxygen (O2) sensors. Oxygen sensors are essential for the ECM to determine the air-fuel mixture in the exhaust. Test the voltage and resistance of both the pre-catalytic converter (upstream) and post-catalytic converter (downstream) O2 sensors on Bank 2 to make sure they are functioning properly. If any sensor is faulty, replace it.

    Step 5: Inspect the fuel system. Check the fuel pressure using a fuel pressure gauge to make sure it's within the manufacturer's specified range. If the fuel pressure is too low, it may cause a lean condition, leading to the P0173 code. Inspect the fuel pump, fuel pressure regulator, and fuel injectors for any signs of malfunction.

    How to Repair P0173

    After diagnosing the root cause of the P0173 code, follow these steps to repair the issue:

    Step 1: Repair vacuum leaks. If vacuum leaks were detected during diagnosis, replace damaged hoses, gaskets, or seals, and make sure all connections are properly secured.

    Step 2: Replace the MAF sensor. If the MAF sensor was found to be faulty, install a new one and reset the ECM.

    Step 3: Replace faulty O2 sensors. If any O2 sensors were determined to be malfunctioning, replace them with new ones.

    Step 4: Repair the fuel system. If the fuel pressure was found to be too low, replace or repair the fuel pump, fuel pressure regulator, or fuel injectors as needed.


    The P0173 code can adversely affect your engine's performance and fuel efficiency. By following the step-by-step guide above, you can diagnose and repair the issues causing the Fuel Trim Malfunction (Bank 2) code. Always remember to reset the ECM after completing the repairs and perform a test drive to ensure the issue has been resolved. It's important to address this code as soon as possible to prevent further damage to the engine or emission components, and to maintain optimal fuel efficiency and engine performance.

    Found 7 results
    Is it Safe to Drive Check Engine Light?
    How to Read Trouble Codes
    Ask a new Topics question
    Sponsored links