Cylinder 8 Fuel Trim at Min Limit
The P02B7 code indicates that the engine control module (ECM) has detected the fuel trim for cylinder 8 is at its minimum limit, meaning the ECM is unable to further reduce fuel delivery to that cylinder. This typically occurs when the air-fuel mixture is too rich, and the ECM has already subtracted as much fuel as possible. Common causes include a faulty fuel injector that is stuck open or leaking, a misfire causing unburned fuel, low fuel pressure, or a vacuum leak. If left unresolved, it can lead to catalytic converter damage, reduced fuel economy, and engine performance issues.
1. Most Common Causes
- Fuel injector on cylinder 8 stuck open or leaking internally
- Faulty fuel pressure regulator causing excessive fuel pressure
- Fuel pump delivering pressure above specification
- Fuel rail pressure (FRP) sensor reading incorrectly or damaged
- Restricted airflow to cylinder 8 (e.g., intake valve, valve seat, stem seal issues)
- Oxygen sensor (O2) or lambda sensor on the relevant bank providing inaccurate readings
- Injector wiring for cylinder 8 shorted to ground (keeping injector open)
- Mechanical engine problem in cylinder 8 (low compression, burnt valve)
- Fuel contamination in engine oil diluting the air-fuel mixture in the cylinder
2. Symptoms You Will Notice
- Check Engine Light illuminated
- Rough idle or engine misfire
- Poor fuel economy
- Failed emissions test
3. Step-by-Step Diagnosis
Step 1: Scan for additional codes and check freeze frame data.
Step 2: Inspect cylinder 8 spark plug and ignition coil for misfire.
Step 3: Perform a fuel injector balance test to check injector flow.
Step 4: Check fuel pressure and compare to specifications.
Step 5: Inspect for vacuum leaks using a smoke machine or propane enrichment.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances as the rich condition can damage the catalytic converter and oxygen sensors. Short trips to a repair shop are acceptable.
How much does it cost to fix?▼
The cost varies depending on the cause. Replacing a fuel injector can cost $150-$400 including labor. If the issue is a spark plug or coil, it may be $100-$250.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.