System Too Lean at Higher Load Bank 1
P2191 indicates that the engine control module (ECM) has detected a lean air-fuel mixture (too much air, not enough fuel) specifically under high load conditions on Bank 1 (the side of the engine containing cylinder #1). This can be caused by vacuum leaks, faulty fuel injectors, a weak fuel pump, a clogged fuel filter, or a malfunctioning mass airflow (MAF) sensor. The condition can lead to reduced power, hesitation, and potential engine damage if not addressed.
01. Most Common Causes
- Vacuum leak (intake manifold, hoses, gaskets)
- Faulty or clogged fuel injector(s)
- Weak fuel pump or clogged fuel filter
- Malfunctioning mass airflow (MAF) sensor
- Exhaust leak before oxygen sensor
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Engine hesitation or stumble under acceleration
- Reduced power or poor performance at highway speeds
- Rough idle or misfire
03. Step-by-Step Diagnosis
Step 1: Scan for codes and record freeze frame data to confirm conditions.
Step 2: Inspect for vacuum leaks using a smoke machine or propane enrichment.
Step 3: Check fuel pressure and volume at the rail; test fuel pump and filter.
Step 4: Clean or test the MAF sensor; compare readings to specifications.
Step 5: Inspect fuel injectors for clogging or leakage; perform balance test if possible.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive for extended periods, as a lean condition can cause engine overheating, detonation, and damage to catalytic converters. Short trips to a repair shop are acceptable.
How much does it cost to fix?▼
The cost varies by cause: a vacuum leak repair may cost $50-$150, while replacing a fuel pump or injectors can range from $200-$800. Diagnostic fees are typically $100-$150.