P0173

Universal

Fuel Trim Malfunction (Bank 2)

Definition source: General OBD-II reference catalog
Definition verification: Not independently verified for display.
Time: Varies by diagnosis and vehicle | Diagnostic difficulty: Medium
Medium Severity

The engine computer adjusts fuel delivery using feedback from the air-fuel control system. This code means it detected an abnormal fuel-trim condition on Bank 2, the side of the engine identified as Bank 2 for that vehicle. The code does not identify a failed part. Depending on the cause, the engine may run poorly, use more fuel, or produce higher emissions, though it may also seem to run normally.

Report an error with this code

⚠️ Before You Begin (Safety First)

If the engine runs roughly, stalls, loses power, or the check-engine light flashes, avoid continued driving and arrange prompt diagnosis; a severe misfire can cause further damage. If the vehicle runs normally, have the fault checked soon and follow the owner's manual for any warning-light guidance.

Common Symptoms

  • No noticeable symptoms; the code may be detected before the driver notices a change.
  • Rough idle or hesitation if the abnormal fuel correction affects engine operation.
  • Reduced power or stalling may occur if the underlying fault significantly disrupts the air-fuel mixture.
  • Increased fuel consumption or emissions may result when fuel delivery is not being corrected as expected.
  • The check-engine light may be on.

Common Causes

  • An intake or vacuum leak can allow unmetered air into the engine and affect fuel correction.
  • A fuel-delivery problem, such as restricted flow or inadequate pressure, can prevent the engine from receiving the fuel it needs.
  • An exhaust leak or a faulty air-fuel feedback sensor can cause the computer to receive misleading information.
  • A problem with air measurement, such as a contaminated or inaccurate airflow sensor, can lead to incorrect fuel calculations.
  • An injector or its electrical connection may not deliver fuel consistently.
  • Wiring, connector, or control-system faults can interfere with fuel-trim monitoring or adjustment.

Diagnostic Steps

  1. Confirm the code with a suitable scan tool and note any other stored codes; related codes can help guide diagnosis.
  2. With the engine off and cool, visually inspect accessible intake hoses and vacuum lines for disconnections, cracks, or obvious damage.
  3. Check accessible electrical connectors and wiring for looseness, corrosion, or visible damage; do not unplug components while the engine is running.
  4. If the scan tool provides fuel-trim data, record the readings and whether the condition appears at idle or during other operating conditions; use vehicle-specific service information to interpret them.
  5. If the fault remains, or the engine runs poorly, arrange testing for intake leaks, fuel delivery, exhaust leaks, and sensor signals before replacing parts.

When to Call a Professional

Use a scan tool to review Bank 2 fuel-trim data and compare it with the other bank under appropriate operating conditions. Check for intake or vacuum leaks, exhaust leaks that could affect feedback, fuel-delivery problems, and implausible sensor readings before replacing parts. Exact test conditions and procedures depend on the model, year, and engine.

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Commonly Asked Questions

Does P0173 prove that a sensor or injector has failed?

No. It reports a fuel-trim malfunction on Bank 2, not a confirmed failed part. Diagnosis should check air leaks, fuel delivery, sensor feedback, wiring, and related codes.

What does Bank 2 mean?

It identifies one side of the engine as designated by the vehicle manufacturer. Its location depends on the engine, so consult model-specific service information rather than assuming a side.

Can the vehicle feel normal with this code?

Yes. Some vehicles show no obvious symptoms, while others may have rough running, hesitation, reduced power, or increased fuel use.

Should parts be replaced as soon as the code appears?

No. Compare scan data and test likely causes first. A code alone does not establish which component, if any, needs replacement.

Browse Available Code Guides

Previous and next available guides in database record order, across makes. Adjacent entries may share a code number and do not necessarily describe related faults.