DTC P0173: Fuel Trim Malfunction (Bank 2)

In the intricate world of automotive diagnostics, diagnostic trouble codes (DTCs) act as guiding lights, illuminating potential issues within a vehicle’s systems. Among these, DTC P0173 takes center stage as a significant indicator of problems related to a fuel trim malfunction in Bank 2. This comprehensive article delves into the causes, symptoms, inspection procedures, and effective solutions for addressing and resolving DTC P0173.

1. Causes of DTC P0173:

DTC P0173 emerges when the Engine Control Module (ECM) detects that the fuel trim in Bank 2 is not operating within the expected range. The underlying causes can encompass:

– Faulty Mass Airflow Sensor (MAF): Incorrect MAF readings can lead to incorrect fuel trim adjustments.

– Malfunctioning oxygen sensor: A malfunctioning oxygen sensor may provide inaccurate feedback to the ECM.

– Vacuum leaks: Unmetered air entering the engine due to vacuum leaks can disrupt proper fuel trim.

– Fuel injector issues: Stuck-open or leaking fuel injectors can affect the fuel mixture.

– Exhaust leaks: Leaks in the exhaust system can lead to incorrect oxygen sensor readings.

2. Symptoms of DTC P0173:

Recognizing the symptoms associated with DTC P0173 aids mechanics in accurately diagnosing the issue:

– Decreased fuel efficiency: Incorrect fuel trim can lead to imbalanced air-fuel mixture and increased fuel consumption.

– Rough engine operation: The engine may exhibit rough idling or hesitations during acceleration.

– Illuminated Check Engine Light (CEL): DTC P0173 triggers the CEL to alert the driver of a potential problem.

3. Inspection of DTC P0173:

Thorough inspection techniques are crucial for accurate diagnosis:

– OBD-II scan: Utilize an OBD-II scanner to retrieve the DTC and accompanying freeze frame data, providing insight into the conditions that activated the code.

– Visual examination: Inspect components such as the MAF sensor, oxygen sensor, and vacuum hoses for proper function.

– MAF sensor testing: Test the MAF sensor’s readings using appropriate diagnostic tools.

– Oxygen sensor testing: Verify the oxygen sensor’s readings and functionality.

4. Resolving Causes of DTC P0173:

Addressing DTC P0173 involves specific steps tailored to the underlying issue:

– MAF sensor replacement: Replace a faulty MAF sensor with a new, high-quality unit.

– Oxygen sensor replacement: If the oxygen sensor is suspected, replace it to ensure accurate feedback to the ECM.

– Vacuum leak repair: Locate and repair vacuum leaks to prevent unmetered air from entering the engine.

– Fuel injector maintenance: Repair or replace faulty fuel injectors to ensure proper fuel delivery.

5. Clearing DTC P0173:

After successfully addressing the root cause, clear the DTC from the ECM’s memory using an OBD-II scanner. This step confirms the issue’s resolution and prevents the recurrence of the CEL.


DTC P0173, indicative of a fuel trim malfunction in Bank 2, emphasizes the intricate balance required for optimal engine performance. Through a comprehensive understanding of its causes, recognition of its symptoms, meticulous inspection techniques, and effective solutions, mechanics can accurately diagnose and rectify this issue. Achieving proper fuel trim remains pivotal for achieving optimal fuel efficiency, engine performance, and overall vehicle functionality.