What Does P0173 Mean?
The ECM has detected a fuel trim malfunction on bank 2. The adaptive fuel trim values have exceeded the ECM's ability to compensate, or the fuel trim correction is behaving erratically. This is a general fuel trim fault code indicating that the air-fuel mixture on bank 2 cannot be properly controlled. The driver may notice rough running, poor fuel economy, or driveability issues on the bank 2 side of the engine.
Common Causes
30%
Vacuum leak on the bank 2 side of the intake manifold or associated hoses
25%
Dirty or failing MAF sensor providing inaccurate airflow measurement
20%
Faulty bank 2 upstream O2 sensor causing incorrect fuel trim correction
15%
Fuel delivery issue — weak pump, clogged filter, or leaking bank 2 injectors
10%
Exhaust leak at the bank 2 exhaust manifold affecting O2 sensor readings
Diagnostic Steps
1
Monitor STFT and LTFT for both banks simultaneously. If bank 2 trims are significantly different from bank 1, the problem is bank-2-specific. If both banks are off similarly, the problem is shared (MAF, fuel pressure, etc.).
2
Perform a smoke test focused on the bank 2 intake runners, intake manifold gasket area, and any vacuum hoses on the bank 2 side of the engine.
3
Swap the bank 1 and bank 2 upstream O2 sensors (if accessible). Clear codes and drive. If the fuel trim problem follows the sensor, replace the faulty sensor.
4
Clean the MAF sensor with MAF-specific cleaner and retest. Compare readings to manufacturer specs at idle and 2500 RPM.
5
Check fuel pressure at the rail under all conditions — key on/engine off, idle, and under snap acceleration. Low or erratic pressure affects both banks.
Estimated Repair Cost
$100 - $700
Parts + labor, varies by vehicle and location
The ECM has detected a fuel trim malfunction on bank 2. The adaptive fuel trim values have exceeded the ECM's ability to compensate, or the fuel trim correction is behaving erratically. This is a general fuel trim fault code indicating that the air-fuel mixture on bank 2 cannot be properly controlle...
The most common cause of P0173 (Fuel Trim Malfunction (Bank 2)) is: Vacuum leak on the bank 2 side of the intake manifold or associated hoses
Typical repair costs for P0173 range from $100 to $700, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Drive with caution. Depending on the direction of the fuel trim malfunction (lean or rich), there may be misfire risk, catalytic converter damage, or reduced power. Avoid sustained high-load driving until the root cause is identified.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0173 to identify the root cause.
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Quick Info
Category
Powertrain
System
Fuel System
Difficulty
Type
Generic (SAE)
Recommended Tools
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