Vacuum leak on the bank 2 intake manifold, such as a cracked hose or failed gasket; Faulty bank 2 oxygen sensor or its wiring, causing inaccurate feedback; Leaking or sticking fuel injector on bank 2, delivering too much or too little fuel; Exhaust leak before the bank 2 oxygen sensor, allowing outside air to skew readings; Low fuel pressure or a weak fuel pump affecting the entire engine but most noticeable on one bank; Dirty or failing mass airflow sensor (MAF) reporting incorrect air volume; Mechanical issue such as low compression or a worn camshaft on bank 2

DTC codes / P01xx · Fuel and air metering / P0173

P0173Fuel Trim Malfunction (Bank 2)

Q: What does code P0173 mean?

Fuel Trim Malfunction (Bank 2). P0173 means the engine computer detected that the fuel mixture on bank 2 is outside the range it can correct using the long-term fuel trim strategy. Bank 2 is the side of the engine that does not contain cylinder number one, and the computer has reached the limit of its ability to add or subtract fuel to bring the air-fuel ratio back to stoichiometric.

P0173 means the engine computer detected that the fuel mixture on bank 2 is outside the range it can correct using the long-term fuel trim strategy. Bank 2 is the side of the engine that does not contain cylinder number one, and the computer has reached the limit of its ability to add or subtract fuel to bring the air-fuel ratio back to stoichiometric.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering

Symptoms you may notice

Illuminated check engine light, often with no other noticeable symptoms
Rough idle or engine misfire, especially when cold or under load
Reduced fuel economy and a richer exhaust smell
Hesitation or stumble during acceleration
Black sooty exhaust smoke or fouled spark plugs over time
In some cases, the engine may enter limp mode and limit power

Common causes, most likely first

Vacuum leak on the bank 2 intake manifold, such as a cracked hose or failed gasket
Faulty bank 2 oxygen sensor or its wiring, causing inaccurate feedback
Leaking or sticking fuel injector on bank 2, delivering too much or too little fuel
Exhaust leak before the bank 2 oxygen sensor, allowing outside air to skew readings
Low fuel pressure or a weak fuel pump affecting the entire engine but most noticeable on one bank
Dirty or failing mass airflow sensor (MAF) reporting incorrect air volume
Mechanical issue such as low compression or a worn camshaft on bank 2

How to diagnose and fix it

Scan all stored codes and freeze-frame data to confirm P0173 is the primary fault and not a consequence of another code
Inspect the bank 2 intake tract and vacuum lines for leaks using a smoke machine or carburetor cleaner
Check fuel pressure and volume against the manufacturer's specification
Examine bank 2 oxygen sensor live data for switching activity and compare with bank 1
Perform a propane enrichment test or injector balance test to isolate a sticking or leaking injector
Inspect the exhaust system for leaks upstream of the bank 2 oxygen sensor
Verify compression and valve timing on bank 2 if all other checks pass

What P0173 really tells you about bank 2

A P0173 can be set by a lazy oxygen sensor that still switches but responds too slowly, so comparing bank 1 and bank 2 sensor waveforms is more revealing than a simple pass/fail test.
Many technicians replace the bank 2 oxygen sensor first, but a vacuum leak at the intake manifold gasket is a more common cause on V6 and V8 engines with age-related gasket shrinkage.
The code does not always mean the engine is running rich; it can also set when the computer has maxed out adding fuel because of a lean condition, so reading long-term fuel trim values is essential.
A failing mass airflow sensor can skew fuel trim on both banks, but bank 2 may hit the limit first due to slight differences in airflow distribution, leading to a misleading single-bank code.
Exhaust leaks upstream of the oxygen sensor draw in outside air and cause the sensor to report a false lean condition, driving fuel trim rich and eventually setting P0173.

Can I keep driving with P0173?

You can usually drive the vehicle with P0173, but avoid heavy acceleration and towing until it is diagnosed, because prolonged driving with incorrect fuel trim can damage the catalytic converter and spark plugs. If the check engine light starts flashing, stop driving and seek service immediately.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.