Fuel Trim Malfunction (Bank 1)
P0170 indicates that the engine control module (ECM) has detected a fuel trim malfunction on bank 1, meaning the air-fuel mixture is too lean or too rich. The ECM adjusts fuel delivery based on oxygen sensor readings; when the adjustment exceeds a calibrated limit, this code sets. Common causes include vacuum leaks, faulty mass airflow (MAF) sensor, clogged fuel injectors, low fuel pressure, or exhaust leaks before the oxygen sensor.
01. Most Common Causes
- Vacuum leak (intake manifold, hoses)
- Faulty mass airflow (MAF) sensor
- Clogged fuel injectors
- Low fuel pressure (fuel pump, filter, regulator)
- Exhaust leak before oxygen sensor
02. Symptoms You Will Notice
- Check Engine Light on
- Rough idle or hesitation
- Poor fuel economy
- Failed emissions test
03. Step-by-Step Diagnosis
Step 1: Scan for additional codes and freeze frame data.
Step 2: Inspect for vacuum leaks using smoke machine or propane.
Step 3: Check MAF sensor readings and clean or replace if dirty.
Step 4: Test fuel pressure and volume; replace pump/filter if low.
Step 5: Inspect oxygen sensor operation and exhaust for leaks.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
You can drive short distances, but prolonged driving may cause poor performance, reduced fuel economy, and potential damage to the catalytic converter. It's best to diagnose and repair promptly.
How much does it cost to fix?▼
Cost varies by cause: a vacuum leak repair may be $50-$150, MAF sensor replacement $100-$300, fuel pump $200-$500. Diagnostic fees are typically $50-$100.