P0173 Code: Fuel Trim Malfunction (Bank 2)
🟠 Moderate severity · drivable
Usually drivable, but the engine may run rough, idle poorly, or waste fuel until the cause is fixed.
What P0173 means
Fuel trim is the computer's adjustment that keeps the air-fuel mixture at the right ratio. This code means the computer has had to correct the mixture too much on bank 2, which points to a problem like a vacuum leak, a bad sensor, or low fuel pressure. It only applies to engines with two cylinder banks, like V6 and V8 engines.
Symptoms
- Check engine light is on
- Rough idle
- Poor fuel economy
- Hesitation or stumbling under load
- Failed emissions test
Common causes
- most common: Vacuum leak letting in unmetered air on bank 2
- common: Dirty or failing mass air flow (MAF) sensor
- common: Low fuel pressure from a weak pump or clogged filter
- less common: Clogged or leaking fuel injector on bank 2
- less common: Exhaust leak before the oxygen sensor on bank 2
How to fix it
| Fix | DIY? | Typical cost |
|---|---|---|
| Find and fix vacuum leaks (hoses, gaskets, intake) | Yes | $5–50 |
| Clean or replace the mass air flow sensor | Yes | $15–150 |
| Check fuel pressure and replace the fuel filter | Mechanic | $100–400 |
| Diagnose and fix injector or exhaust leak problems | Mechanic | $100–500 |
Frequently asked questions
Can I drive with a P0173 code?
Yes, in most cases. The car will still run, but you may notice rough idle, poor fuel economy, or hesitation until it's fixed.
What does "bank 2" mean?
Bank 2 is the cylinder bank that does not contain cylinder number one. This code only applies to V6, V8, and other multi-bank engines.
What is the most common cause of P0173?
A vacuum leak on bank 2, with MAF sensor and fuel pressure problems close behind.
Related codes
P0170
P0170 Code: Fuel Trim Malfunction (Bank 1)
P0174P0174 Code: System Too Lean (Bank 2)
P0175P0175 Code: System Too Rich (Bank 2)
Updated 2026-08. This page is informational and not a substitute for professional diagnosis.