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, this code is set. Common causes include vacuum leaks, faulty mass airflow (MAF) sensor, clogged fuel injectors, low fuel pressure, or exhaust leaks before the oxygen sensor. This code often appears alongside P0171 or P0174.
1. Most Common Causes
- Faulty or slow-responding oxygen sensor on Bank 2
- Contaminated or miscalibrated mass airflow (MAF) sensor
- Air intake leaks on Bank 2
- Clogged or mechanically faulty fuel injectors on Bank 2
- Faulty manifold absolute pressure (MAP) sensor
- EVAP canister purge valve stuck open
- Wiring or connector issues with the Bank 2 oxygen sensor
- Internal engine control module (ECM/PCM) failure
2. Symptoms You Will Notice
- Check Engine Light on
- Rough idle or hesitation
- Poor fuel economy
- Failed emissions test
- Possible misfire
3. Step-by-Step Diagnosis
Step 1: Scan for additional codes and freeze frame data.
Step 2: Inspect for vacuum leaks using a smoke machine or propane enrichment.
Step 3: Check fuel pressure and volume; test fuel injectors for balance.
Step 4: Clean or test MAF sensor; inspect air intake for leaks.
Step 5: Monitor oxygen sensor readings and fuel trim values with a scan tool.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
You can drive short distances, but it may cause poor performance, reduced fuel economy, and potential damage to the catalytic converter if ignored. It's best to diagnose and repair promptly.
How much does it cost to fix?▼
Diagnosis typically costs $50-$150. Repairs vary: cleaning MAF sensor ($10-$50), replacing a vacuum hose ($20-$100), or replacing a fuel injector ($150-$400). Total cost depends on the root cause.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.