Fix P2189: Mechanic’s solutions that WORKED

The code P2189: System Too Lean at Idle Bank 2 points out that there is an issue with the air-to-fuel ratio being too lean (too much air, not enough fuel) at idle in Bank 2 of the engine. This imbalance can affect engine performance and fuel efficiency. The cause is often related to air intake or fuel delivery systems, and the problem is more prevalent at idle speed.

P2189 quick overview

Meaning	P2189: System Too Lean at Idle Bank 2
Is it serious?	This code indicates an imbalance in the air-to-fuel ratio, which can lead to engine performance issues, but it typically does not cause an immediate breakdown.
Possible causes	– Vacuum leaks in the intake system – Faulty or dirty Mass Air Flow (MAF) sensor – Leaks in the PCV (Positive Crankcase Ventilation) system – Faulty oxygen sensors – Fuel delivery issues (such as a weak fuel pump or dirty fuel injectors) – Exhaust leaks before the oxygen sensors – Incorrect fuel type (like using E85 in a non-flex fuel vehicle)
How to diagnose?	Conduct a Smoke Test: Check for vacuum leaks in the intake system. Inspect MAF Sensor: Ensure the Mass Air Flow sensor is clean and functioning properly. Check PCV System: Examine the PCV valve and hoses for leaks or damage. Evaluate Oxygen Sensors: Assess the condition and performance of the oxygen sensors. Inspect Fuel System: Verify fuel pressure and quality; check for any fuel delivery issues. Look for Exhaust Leaks: Search for any leaks in the exhaust system, especially before the oxygen sensors. Check Fuel Type: Confirm that the correct type of fuel is being used for the vehicle.

How to fix P2189 – learn from mechanics

I looked into P2189 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: Mercedes

Vehicle Information: 2006 Mercedes-Benz R350 4Matic 3.5L

Issue + Repair History:

• Originally came in with a misfire and multiple codes.
• Found that tumble doors in the intake were damaged.
• Replaced the intake assembly and spark plugs.
• After initial repair, faced adapt at limit codes, rich and lean codes for both banks.
• Replaced MAF sensor with a Bosch unit, which initially seemed to resolve the issue.
• However, faced a pending P2189 code and P0749, P2095 codes again.

Other OBD2 Codes + Test Results:

• P0745: Adaptation at limit, Idle, Rich, right bank
• P0749: Adaptation at limit, Idle, Rich, left bank
• P2187: Lean right bank, at idle
• P2189: Lean left bank, at idle
• Fuel pressure tested and found to be good.

Suggestions to Fix Issue:

• Conduct a compression test to check for possible valve damage.
• Ensure the air filter housing is fully seated on the MAF sensor.
• Verify O2 sensor connectors, ensuring they are not mismatched or swapped.
• Check for any air leaks in the system.

What was the Final Fix:

• A small leak was found in one of the PCV hoses using a smoke test. Repairing the leak resolved the issue.

Case #2: Porsche

Vehicle Information: 2006 Porsche Cayman S 3.4L

Issue + Repair History:

• Experienced hard starts and stalling after the first fuel fill-up.
• Displayed P2189 code with no driveability issues initially.
• Hard start with stalling occurred again after short stops, with rough running for 3-5 minutes.
• Problem only occurred during hot starts; cold starts were normal.
• Replaced engine with a used one, along with the left-hand converter, left O2 sensors, and new fuel and oil caps.

Other OBD2 Codes + Test Results:

• P2189: System Too Lean at Idle
• Fuel pressure tested: 55 PSI at idle, 57-59 PSI at 2500 RPM no load, drops to 40 PSI in 10 minutes, and 30 PSI in 30 minutes when the engine is off.

Suggestions to Fix Issue:

• Check for large intake leaks, particularly around the oil fill tube, vacuum source for power brake booster, and oil separator/PCV valve.
• Conduct a smoke test on the intake and crankcase to detect any leaks.
• Consider the possibility of an issue with the canister purge valve, located on the top front left side of the engine.
• Investigate if fuel trims are higher at idle.

What was the Final Fix:

• A vacuum leak was found and repaired at the throttle body.
• Identified and resolved an issue with the vent solenoid under the intake, where the connector was crossed with the flapper control solenoid.
• After these repairs, the Porsche ran smoothly without further issues.

Case #3: Land Rover

Vehicle Information: 2014 Land Rover LR4 HSE 3.0L

Issue + Repair History:

• Lean codes for both Bank 1 and Bank 2.
• At idle, short-term fuel trim was 2, long-term fuel trim was 45 for both banks.
• After clearing adaptations, short-term fuel trim immediately increased to 20%, while long-term fuel trim quickly rose back to 45% within about 2 minutes.
• No leaks found during a smoke test of the intake.
• Suspected issue with PCV diaphragm in the right side valve cover.

Other OBD2 Codes + Test Results:

• P2187: Bank 1 – too lean
• P2189: Bank 2 – too lean

Suggestions to Fix Issue:

• Check fuel pressure and MAF readings.
• Replace the PCV valve, as it’s a common issue in this model.
• Consider using a high-pressure smoke machine for testing.
• Inspect cam VVT hubs as they can sometimes cause similar issues.
• Examine valve cover and PCV for any leaks.
• Check for high crankcase vacuum as an indicator of PCV system failure.

What was the Final Fix:

• Replacing the PCV diaphragm resolved the issue.
• Initially, the high-pressure smoke machine did not reveal the problem at the diaphragm, possibly because the pressure was sealing it during testing.
• Crankcase pressure was also tested and found to be normal.

Case #4: Mazda

Vehicle Information: 2005 Mazda 6 S 3.0L

Issue + Repair History:

• Initially, the vehicle came in with more than 10 codes. After clearing codes and disconnecting the battery, the MIL returned with P2189: bank-2 lean at idle.
• Various tests conducted, including smoke test and checking EGR and MAF sensors.
• Replaced vacuum hoses previously.
• No leaks were found during the smoke test, and fuel trims were bouncing significantly.

Other OBD2 Codes + Test Results:

• P2189: System too lean at idle on Bank-2

Suggestions to Fix Issue:

• Check the purge valve for sticking open, as it could cause fuel trims to be off.
• Consider an injector issue and check fuel pressure.
• Review ignition traces and possibly substitute the MAF sensor.
• Inspect the PCV hose from the back of the intake manifold.
• Pinch off the line to the purge valve and observe fuel trim changes.

What was the Final Fix:

• The issue was resolved by replacing the Purge Control Solenoid Valve. Pinching off the hose to the valve immediately showed a reaction in long-term and short-term fuel trims.
• The replacement of the valve fixed the issue, and the vehicle ran fine after several test drives without any complaints.

Case #5: Hyundai

Vehicle Information: 2009 Hyundai Santa Fe GLS 2.7L

Issue + Repair History:

• Initially came in with extended crank when cold and a check engine light. After clearing codes, only P2187 and P2189 returned.
• Live data showed fuel trims around +2%, but freeze frame data showed +24% long term and -11% short term.
• Customer had filled the tank with E85 fuel, which was partially corrected by refilling with the correct fuel.
• Various tests conducted including blocking off the purge valve and swapping the MAF sensor, but no change observed.
• The vehicle continued to show lean codes after being driven.

Other OBD2 Codes + Test Results:

• P2187: Fuel system too lean at Idle B1
• P2189: Fuel system too lean at Idle B2

Suggestions to Fix Issue:

• Check fuel volume and quality to ensure no E85 remains.
• Test for ethanol content above 15% as it can cause issues in Hyundai vehicles.
• Inspect the intake manifold for leaks, especially where the variable runner actuator shaft enters.
• Check the front motor mount for vacuum leaks.
• Reset the ECM to recalibrate fuel trim monitoring.
• Review live data for MAF sensor readings and replace with an OEM or different aftermarket sensor if necessary.

What was the Final Fix:

• The issue was resolved after completely cleaning out the E85 from the tank and refilling with the correct fuel, taking two fills to achieve this.
• The vehicle later returned with a P0420 code, possibly related to the use of E85, but was cleared and monitored for recurrence.

Advice	Diagnostic Step
Check for Vacuum Leaks	Perform a thorough inspection of the intake system and surrounding areas for any signs of vacuum leaks.
Inspect PCV System	Examine the PCV valve and hoses for any malfunctions or leaks, as these can contribute to a lean condition.
Test Fuel System	Evaluate the fuel pressure and quality, ensuring that the correct fuel type is used and the system is delivering fuel properly.
Examine O2 Sensors	Review the performance of oxygen sensors to ensure they are functioning correctly and not contributing to the lean condition.
Inspect Purge Valve	Check the purge control solenoid valve for sticking or leaks, as this can affect the fuel system’s balance.
Check MAF Sensor	Evaluate the Mass Air Flow sensor for accurate readings and consider replacing it if necessary.
Smoke Test Intake System	Perform a smoke test to visually identify any hard-to-find leaks in the intake system.
Evaluate Fuel Trim Data	Monitor short-term and long-term fuel trims for irregularities that could indicate the source of the lean condition.