P0173 moderate

Fuel Trim Malfunction (Bank 2)

The P0173 code means the vehicle's onboard diagnostic system has detected: Fuel Trim Malfunction (Bank 2). This is a moderate severity code.

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Keep driving?: Short distances only
DIY difficulty: moderate
Estimated cost: $50 - $500 (parts and labor)

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Common Symptoms

Check Engine Light on
Rough idle
Poor fuel economy
Hesitation during acceleration

Probable Causes (Ranked by Likelihood)

Large vacuum leak on Bank 2 side Very High
Faulty mass airflow sensor High
Clogged fuel injectors on Bank 2 Moderate
Failing fuel pressure regulator Moderate

Step-by-Step Diagnostic Procedure

Check long-term fuel trim (LTFT) values for Bank 2; values beyond plus or minus 25% confirm a fuel trim malfunction
Inspect intake manifold gaskets and vacuum hoses on the Bank 2 side for leaks using a smoke machine
Clean or test the MAF sensor; compare readings to manufacturer specifications
Test fuel pressure at the rail and check for pressure drop under load

Frequently Asked Questions

What does fuel trim malfunction mean?

Fuel trim is the ECM adjustment to the air-fuel mixture. P0173 means the Bank 2 fuel trim correction has exceeded the ECM threshold, indicating the engine cannot properly maintain the correct air-fuel ratio on that bank.

How is P0173 different from P0174?

P0173 is a general fuel trim malfunction code for Bank 2 that indicates the fuel trim is outside normal operating limits. P0174 specifically indicates a lean condition on Bank 2. P0173 can be triggered by either rich or lean fuel trim deviations.

Can a bad catalytic converter cause P0173?

A clogged catalytic converter can cause back-pressure that affects fuel trims, but it is not a common cause. A failed converter is more likely to set catalyst efficiency codes like P0430.