P0170 Code: Fuel Trim Malfunction (Bank 1)
🟠 Moderate severity · drivable
Usually drivable, but the engine may run rough, idle poorly, or waste fuel until the cause is fixed.
What P0170 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 1, which points to a problem like a vacuum leak, a bad sensor, or low fuel pressure. The code is set when the correction goes outside the expected range.
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
- 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
- less common: Exhaust leak before the oxygen sensor
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 P0170 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 is fuel trim?
It's the computer's adjustment to the air-fuel mixture to keep it at the ideal ratio. This code means it has to correct too much.
What is the most common cause of P0170?
A vacuum leak that lets unmetered air into the engine, with MAF sensor and fuel pressure problems close behind.
Related codes
P0171
P0171 Code: System Too Lean (Bank 1)
P0172P0172 Code: System Too Rich (Bank 1)
P0174P0174 Code: System Too Lean (Bank 2)
Updated 2026-08. This page is informational and not a substitute for professional diagnosis.