Fix P2191: Mechanic’s solutions that WORKED

The OBD2 code P2191 signifies a situation where the engine runs too lean (i.e., not enough fuel in the mixture) when operating under higher loads. Running lean can cause a range of engine performance issues, from minor hesitations to significant power loss. The diagnosis and repair processes for this code often involve detailed inspection and correction of the fuel delivery system, as well as ensuring the air intake system is functioning correctly.

P2191 quick overview

Meaning	P2191: System too lean at higher loads
Is it serious?	Yes, because it can lead to poor engine performance, increased wear, and potential engine damage over time.
Possible causes	– Vacuum leaks – Faulty fuel injectors – Inadequate fuel pressure – Contaminated Mass Air Flow (MAF) sensor – Exhaust leaks – PCV valve issues
How to diagnose?	Perform a smoke test to identify any vacuum leaks. Inspect the fuel injectors for proper operation and cleanliness. Measure fuel pressure to ensure it meets specifications across all engine loads. Clean or replace the MAF sensor if it’s dirty or faulty. Check the PCV valve for proper operation. Update the ECM software if applicable, to ensure optimal engine management.

How to fix P2191 – learn from mechanics

I looked into P2191 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.

Case #1: Hyundai

Vehicle information 2012 Hyundai Veloster 1.6L

Issue + repair history

• Persistent P2191 lean under load fault.
• Quality fuel always used.
• Checked for intake system leaks, none found.
• Monitored O2 sensors and freeze frame data, no abnormalities except for LTFT at 26%.
• Flushed injectors twice with top engine cleaner.
• Used Chevron Techron in recent fuel tanks.
• Replaced OEM Denso O2 sensor and MAP sensor.
• Replaced PCV.
• Monitored fuel pressure, ranging from 550psi at idle to 2300psi at wide open throttle.
• Replaced spark plugs due to mileage (95k).
• Occasional slight miss when cold.
• ECM updated at the dealer.
• Experienced one instance of low fuel pressure (65psi) at idle, resolved after cycling the key.
• No extended crank during low fuel pressure incidents.

Other OBD2 Codes + Test Results

• P2191: Bank 1 lean under load

Mechanic suggestions

• Check exhaust back pressure.
• Consider a leak down test to check for valve sealing issues.
• Verify proper operation of the variable intake system.
• Ensure fuel pressures match desired levels on both sides of the high-pressure fuel pump.
• Investigate the possibility of injector issues, as they may have caused carbon buildup on intake valves.
• Consider E85 fuel contamination if available in the area.

Final fix

• Replaced injectors and walnut blasted intake valves due to severe carbon buildup.
• Vehicle now runs smoothly with long-term fuel trim hovering around 0%.

Case #2: Hyundai

Vehicle information 2014 Hyundai Accent GS 1.6L

Issue + repair history

• Occasional SES light with P2191 code.
• Idle is fine, good power at all loads.
• Replaced O2 sensor and intake manifold gaskets previously.
• Fuel system service, PCV valve, spark plugs, lambda O2 sensor, intake gaskets, fuel injectors, and vacuum hoses replaced by dealer previously.
• Dealer never performed a PCM reflash.
• Intermittent P0441 and P0304 codes reported by dealer but not investigated further.

Other OBD2 Codes + Test Results

• P2191: System Too Lean at Higher Loads
• Fuel Pressure @ Idle: 580 psi
• Fuel Pressure @ WOT: 2200 psi
• Fuel Adaptation @ Part Load: 1.26
• Fuel Adaptation @ Idle: 0.9-1.0

Mechanic suggestions

• Check PCV valve for operation and leaks; consider replacing.
• Perform a volumetric efficiency test to check MAF reporting.
• Consider reprogramming ECM due to a rich under load PCM update.
• Check for vacuum leaks with a smoke machine.
• Monitor low fuel pressure pump pressure under load and inspect fuel delivery volume.
• Inspect purge valve for operation/leaks and program ECM per TSB #17-FL-001 released in February 2017.
• Verify fuel quality and consider cleaning or replacing the MAF sensor.
• Check engine ground integrity, as a bad ground could cause issues.

Final fix

• Re-flashed PCM, resolving the issue with the SES light not returning after subsequent drives.

Case #3: Toyota

Vehicle information 2015 Toyota Camry LE 2.5L

Issue + repair history

• Occasional MIL (Malfunction Indicator Lamp) with P2191 code.
• No noticeable drivability issues reported by the owner.
• Routine maintenance up-to-date; no recent repairs related to the fuel system or intake.

Other OBD2 Codes + Test Results

• P2191: System Too Lean at Higher Loads

Mechanic suggestions

• Check for vacuum leaks using a smoke machine to ensure there are no air intake leaks affecting the air-fuel ratio.
• Perform a fuel pressure test to ensure the fuel system is operating within specifications under load conditions.
• Inspect the MAF (Mass Air Flow) sensor for dirt or contamination that may affect its accuracy and clean or replace it if necessary.
• Verify proper operation of the PCV (Positive Crankcase Ventilation) valve and hoses to prevent unmetered air from entering the intake manifold.
• Review the long-term fuel trim data to identify any abnormalities that may indicate a lean condition under load.
• Check the integrity of the exhaust system for leaks that could affect the oxygen sensor readings and cause false lean condition codes.
• Consider updating the engine control module (ECM) software to address any known issues related to fuel trim control or oxygen sensor diagnostics.

Final fix

• After thorough inspection, it was found that the PCV valve was stuck open, allowing excess air into the intake manifold, causing the lean condition under load. Replacing the PCV valve resolved the issue, and the MIL (Malfunction Indicator Lamp) did not return after subsequent drives.

Diagnostic Step	Brief Explanation
Perform a smoke test	Identifies leaks in the intake system that could lead to a lean condition.
Inspect the fuel injectors	Ensures they are delivering the correct amount of fuel.
Measure fuel pressure	Confirms the fuel pump and pressure regulator are maintaining proper pressure.
Clean or replace the MAF sensor	Guarantees accurate measurement of air entering the engine.
Check the PCV valve	Verifies it isn’t stuck open, which could introduce extra air into the engine.
Update the ECM software	Applies manufacturer updates to improve fuel and air management.

In these service cases, the solutions to the P2191 code varied from cleaning and replacing injectors and the PCV valve to re-flashing the PCM and ensuring no vacuum leaks were present. Each fix targeted the root cause of the lean condition, whether it was an air intake issue or a fuel delivery problem, ultimately restoring proper air-fuel balance and engine performance.