P0173
Fuel Trim (Bank 2)
- Severity
- Medium
- Driving
- Drivable — book it in
The fuel trim on bank 2 is outside its normal working range, without the module committing to whether the mixture is too lean or too rich. Fuel trim is the correction the module applies to its base fuel calculation; when that correction has to become large, something upstream is wrong.
Possible causes
- CommonVacuum leak in the intake system
- CommonFaulty mass airflow sensor
- PossibleFuel delivery problem - pump, filter or regulator
- PossibleFailing oxygen sensor
- PossibleExhaust leak ahead of the oxygen sensor
What you might notice
- Rough idle
- Hesitation under load
- Check engine light on
- Fuel economy worse than usual
What to check, in order
- Read the actual fuel trim values on the live data screen. The direction and size of the correction tells you far more than the code alone.
- Positive trim means the module is adding fuel - look for vacuum leaks or weak fuel delivery.
- Negative trim means the module is cutting fuel - look for high fuel pressure or a leaking injector.
- Check whether trim changes between idle and higher engine speed. A leak that matters only at idle points at a vacuum leak.
- Check for other stored codes. A MAF or oxygen sensor code alongside this one usually names the real cause.
Read this code from your own car
Plug an ELM327 adapter into the OBD-II port under the dashboard. Pin16 reads every stored, pending and permanent code, explains each one like this page does — offline, with no account — and shows what the car recorded when the fault was set.
Where this code sits
P00xxP01xxP02xxP03xxP04xxP05xxP06xxP07xxP08xxP09xxP0AxxP0BxxP0CxxP0DxxP0ExxP0FxxP10xxP11xxP12xxP13xxP14xxP15xxP16xxP17xxP18xxP19xxP1AxxP1BxxP1CxxP1DxxP1ExxP1FxxP20xxP21xxP22xxP23xxP24xxP25xxP26xxP27xxP28xxP29xxP2AxxP2BxxP2CxxP2DxxP2ExxP2FxxP30xxP31xxP32xxP33xxP34xxP35xxP36xxP37xxP38xxP39xxP3AxxP3BxxP3CxxP3DxxP3ExxP3Fxx
Fuel and air metering
P0100P0101P0102P0103P0104P0105P0106P0107P0108P0109P0110P0111P0112P0113P0114P0115P0116P0117P0118P0119P0120P0121P0122P0123P0124P0125P0126P0127P0128P0129P0130P0131P0132P0133P0134P0135P0136P0137P0138P0139P0140P0141P0142P0143P0144P0145P0146P0147P0148P0149P0150P0151P0152P0153P0154P0155P0156P0157P0158P0159P0160P0161P0162P0163P0164P0165P0166P0167P0168P0169P0170P0171P0172P0173P0174P0175P0176P0177P0178P0179P0180P0181P0182P0183P0184P0185P0186P0187P0188P0189P0190P0191P0192P0193P0194P0195P0196P0197P0198P0199