Fuel Trim Malfunction Bank 2
P0173 indicates that the engine control module (ECM) has detected a fuel trim malfunction on Bank 2 (the side of the engine opposite cylinder #1). Fuel trim refers to the ECM's adjustment of fuel delivery to maintain the ideal air-fuel ratio. When the long-term fuel trim exceeds a calibrated threshold (typically ±25%), the code is set. This can be caused by vacuum leaks, faulty oxygen sensors, fuel pressure issues, or MAF sensor problems. Bank 2 is usually the passenger side on V6/V8 engines.
01. Most Common Causes
- Vacuum leak on Bank 2
- Faulty oxygen sensor (Bank 2, Sensor 1)
- Fuel pressure regulator issue
- Clogged fuel injector on Bank 2
- Mass airflow (MAF) sensor contamination or failure
- Exhaust leak before oxygen sensor
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Rough idle or hesitation
- Poor fuel economy
- Failed emissions test
- Engine misfire or surging
03. Step-by-Step Diagnosis
Step 1: Scan for additional codes and freeze frame data to identify conditions when code set.
Step 2: Inspect for vacuum leaks on Bank 2 using smoke machine or propane enrichment.
Step 3: Monitor oxygen sensor readings with a scan tool; compare Bank 1 and Bank 2 sensor 1 voltages.
Step 4: Check fuel pressure and fuel trim values at idle and under load.
Step 5: Inspect MAF sensor for contamination; clean or replace if necessary.
Step 6: Test fuel injectors on Bank 2 for proper spray pattern and flow.
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 catalytic converter damage or poor performance. 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, oxygen sensor replacement $100-$200, MAF sensor $150-$400. Diagnostic fees are typically $100-$150.