Fuel Trim Bank 2
What it means
P0173 means the ECM's fuel-trim adjustments for bank 2 have reached their limit — it can no longer keep the air/fuel mixture correct on that bank. It can be caused by either a lean condition (like a vacuum leak) or a rich one (like a leaking injector), so the first step is reading fuel trims to see which way the mixture is off. The engine generally still runs, but expect rough idle, poor economy, and reduced power until the underlying cause is fixed.
Can I keep driving? Usually drivable, but the engine may idle roughly, hesitate, or lose power; a large trim error can foul plugs or the catalyst over time, so fix it soon.
Common symptoms
What you'll notice
- Check-engine light on
- Rough idle or hesitation
- Poor fuel economy
- Reduced power or surging
Common causes
Most likely first
- Vacuum or intake air leak (drives the mix lean)Likely
- Leaking or restricted fuel injector, or fuel-pressure problem (drives it rich)Common
- Faulty or contaminated mass airflow (MAF) sensorCommon
- Faulty upstream O2 sensor on bank 2Less often
- Skewed engine coolant temp sensor affecting fuelingLess often
How to diagnose & fix
Work through it in order
- Read short- and long-term fuel trims on bank 2 to see whether the ECM is compensating for a lean or rich condition.
- If lean: check for vacuum/intake leaks and unmetered air, and inspect the MAF.
- If rich: test fuel pressure and check injectors for leaking or sticking.
- Review the bank 2 O2 sensor and coolant temp sensor data for plausibility.
- Repair the root cause, then clear and re-test to confirm trims return to normal.
FAQ
Quick answers
Is it safe to drive with P0173?+
Can I just clear P0173?+
Related codes
Often seen with P0173
Read & clear P0173 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.