Fuel and air

P0170 — Fuel Trim Malfunction (Bank 1)

Severity: medium Drive with care, to a shop

What P0170 means

The engine control module constantly adjusts fuel delivery based on oxygen sensor feedback, using short-term and long-term fuel trims. P0170 sets when Bank 1 trim moves outside its allowed limits and the ECM can no longer hold the correct air-fuel ratio. It tells you the mixture is too lean or too rich, not which part is at fault.

Symptoms

  • Check Engine Light on
  • Poor fuel economy
  • Rough idle or occasional stalling
  • Hesitation when accelerating
  • Black smoke from the tailpipe when running rich
  • Possible misfires
  • May later set P0171 or P0172

Possible causes

  1. Dirty or faulty mass air flow (MAF) sensor
  2. Unmetered air leaks after the MAF: hoses, intake boot, intake manifold gasket
  3. Inaccurate or worn oxygen sensor
  4. Low or unstable fuel pressure: filter, regulator, pump
  5. Leaking or clogged fuel injectors
  6. Exhaust leak ahead of the oxygen sensor
  7. PCV system or EGR valve problems

How to diagnose

  1. Read freeze frame data and any other codes, especially P0171, P0172, MAF or misfire codes
  2. Watch short-term and long-term fuel trims on a scan tool at idle and around 2,500 rpm
  3. Inspect intake hoses, air duct and vacuum lines for cracks and loose connections
  4. Check MAF readings and sensor condition, and clean it with MAF cleaner if needed
  5. Test fuel pressure and how well it holds after shutoff
  6. Check oxygen sensor response on the scan tool graph
  7. Look for exhaust leaks upstream of the sensor
  8. Test injectors and compare cylinder balance

Common fixes

  • Clean or replace the MAF sensor
  • Repair intake and vacuum leaks: hoses, boots, gaskets
  • Replace a faulty oxygen sensor
  • Fix fuel delivery: filter, regulator or pump
  • Clean or replace fuel injectors
  • Repair exhaust leaks and clean or fix the PCV or EGR system

Questions and answers

What does code P0170 mean?

The ECM can't correct fuel delivery enough on Bank 1, so the air-fuel mixture is out of range. Common causes are a MAF sensor problem, an air leak or low fuel pressure.

Can I drive with P0170?

For a short time, yes, but get it diagnosed soon. Driving for a long period can cause unstable running and damage the catalytic converter.

What should I check first for P0170?

Start by reading fuel trim values on a scan tool and inspecting the intake for air leaks. Then check and clean the MAF sensor and test fuel pressure.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.