Technical Description of OBD-II Trouble Code
Bank 1 is Experiencing a Lean Condition at Higher Load
What does that mean?
This particular diagnostic trouble code is commonly found in fuel injected engines manufactured by European and Asian car makers since 2010.
These manufacturers include, but are not limited to, Volkswagen, Audi, Mercedes, BMW/Mini, Hyundai, Mazda, Kia, and Infiniti.
The code primarily focuses on the air/fuel ratio sensor, also known as the oxygen sensor, located in the exhaust system. This sensor assists the vehicle’s powertrain control module (PCM) in regulating the amount of fuel injected into the engine. The PCM has detected a lean condition, indicating an excessive amount of air in the air/fuel ratio. The code specifically pertains to Bank 1, which consists of cylinder number 1. The cause of the lean condition can be either a mechanical or electrical circuit fault, depending on the vehicle manufacturer and fuel system.
The troubleshooting steps may vary depending on the manufacturer, type of fuel system, type of mass airflow sensor (MAF), wire colors, and type of air/fuel ratio sensor/oxygen sensor (AFR/O2) and wire colors.
Symptoms
The symptoms associated with the P2191 engine code may include:
Causes
Possible causes for this code to be triggered are:
Diagnostic and Repair Procedures
It is always recommended to check for technical service bulletins (TSB) specific to your vehicle. There may be a known issue with a known fix provided by the manufacturer, which can save time and money during diagnosis.
First, check if there are any other diagnostic fault codes present. If there are any fuel/fuel system related codes, diagnose and address them first. Misdiagnosis can occur if this code is diagnosed before thoroughly diagnosing and dismissing any fuel related system codes. Ensure that there are no intake or exhaust leaks, as an intake or vacuum leak can cause the engine to run lean. An exhaust leak can give the impression of a lean running engine based on the AFR/O2 sensor readings.
Next, locate the air/fuel ratio sensor/oxygen sensor and the mass airflow sensor in your specific vehicle. Here is an example of a MAF sensor:
Once located, visually inspect the connectors and wiring. Look for any signs of chafing, rubbing, bare wires, burn spots, or melted plastic. Separate the connectors and carefully examine the terminals inside. Check for corrosion, burns, or any abnormal green coloration. If necessary, use Electrical Contact cleaner or rubbing alcohol and a light plastic bristle brush to clean the terminals. After cleaning, let them air dry and apply dielectric silicone compound to the terminals.
If you have a scan tool, clear the diagnostic trouble codes from memory and check if the code returns. If it does not return, the issue was most likely related to the connections.
If the code does return, the next step is to test the voltage signal from the MAF sensor to the PCM. Monitor the MAF sensor voltage using a scan tool. If a scan tool is not available, use a digital volt ohm meter (DVOM) to test the signal coming from the MAF sensor. With the sensor connected, connect the red voltmeter lead to the MAF sensor signal wire and the black voltmeter lead to ground. Start the engine and monitor the MAF sensor input as the engine RPM increases. The MAF sensor signal should increase accordingly. Refer to the manufacturer’s specifications for the expected voltage at a given RPM. If the MAF sensor fails this test, replace it and retest.
If the previous tests have passed and the code is still present, monitor the air/fuel ratio sensor/oxygen sensor (AFR/O2). If it consistently indicates a lean running engine, investigate all possible causes of a lean condition. These may include:
Once again, it is crucial to diagnose any other codes before addressing this one, as issues that trigger other codes can also trigger this code.
