P0170 Code: Fuel Trim Malfunction (B1) — Causes & Fix
P0170 means the fuel trim on bank 1 has drifted beyond its correction limits — the ECM can no longer keep the mixture correct.
- Applies to
- All OBD-II vehicles (any make or model)
- Est. repair cost
- $40 – $600
- Time to fix
- 30 minutes – 2 hours
What it means
Causes include vacuum/air leaks, a dirty MAF, fuel-pressure problems, injector issues, or an exhaust leak. P0170 is a generic OBD-II powertrain code defined in the SAE J2012 standard, so it applies to virtually any 1996-or-newer petrol car or light truck regardless of make. Fix the underlying fault, then clear the code with an OBD-II scan tool — it will return if the problem isn't resolved.
Symptoms
- Check engine light on
- Rough idle, hesitation, or stalling
- Poor economy or power
How to fix it
- 1
Check for air and vacuum leaks
1. Inspect intake boots and vacuum lines. 2. Clean the MAF sensor.
- 2
Check fuel delivery
1. Test fuel pressure and injector operation. 2. Repair the root cause, then clear the code.
Frequently asked questions
Is P0170 lean or rich?
It means trim is out of range in either direction. Read live fuel-trim data to see whether the engine is running lean or rich, then chase that cause.
Last updated July 19, 2026
Guidance only — always consult a qualified professional or the official service manual before carrying out repairs.