The oxygen sensor is a device that monitors oxygen content in the exhaust stream to help regulate the air-fuel ratio in the engine. The powertrain control module (PCM) uses information from the oxygen sensor to determine how much fuel should be injected into the engine. If the PCM detects a lean mixture (too much air versus fuel) in the system, the vehicle’s computer will record a P2191 code on a scan tool.
What Does the P2191 Code Mean?
Diagnostic trouble code (DTC) P2191 stands for “Manifold Absolute Pressure/Mass Air Flow – Throttle Position.” This is a generic powertrain code that applies to select vehicles with OBD II.
The oxygen sensor is either installed in the exhaust manifold or located downstream in the exhaust pipe. A sensor that’s located near the outlet of the manifold is responsible for detecting the air-fuel mixture for all cylinders in the exhaust system. Some vehicles can have as many as four oxygen sensors monitoring the oxygen content throughout the exhaust system. This ensures the engine doesn’t run rich or lean. A rich mixture means that there’s too much fuel in the air-fuel mixture while a lean mixture means there’s too much air in the air-fuel mixture. If the engine’s air-fuel ratio is rich or lean, the vehicle might exhibit performance issues or even break down due to faulty parts.
The vehicle’s computer uses the oxygen sensor to determine how much fuel is needed. The PCM will set a P2191 code if the PCM detects a lean mixture in Bank 1. Bank 1 refers to a bank of cylinders that contain cylinder number 1. The location of this cylinder depends on your vehicle’s make and model.
Note: The definition of code P2191 might be different depending on the vehicle manufacturer. Consult the appropriate repair manual or repair database for the exact code definition.
What are the Common Causes of the P2191 Code?
- Faulty fuel injector(s)
- Weak fuel pump
- Faulty oxygen sensor
- Faulty mass air flow sensor
- Faulty PCM or software in need of an update
What are the Common Symptoms of the P2191 Code?
- Illuminated check engine light
- Engine lacks power
- Engine misfires
- Reduced fuel efficiency
How to Diagnose the P2191 Code
There might be more than one DTC stored in your PCM. Make sure to check the scan tool thoroughly when diagnosing your vehicle, so you don’t miss anything. Follow the recommended diagnostic steps for your vehicle as indicated in the repair manual. What might work to resolve a P2191 code in a Kia Soul might not work for a Hyundai Accent.
However, we strongly encourage you to take your vehicle to an expert if you lack the skills and knowledge to perform a diagnosis with a scan tool.
How to Fix the P2191 Code
There’s no magic bullet for troubleshooting DTCs. You’ll have to find the underlying causes of a P2161 code to figure out what repairs or replacements are needed. Lucky for you, there are numerous resources online for trouble codes like this one. We suggest searching for technical service bulletins published by your vehicle’s manufacturer to save time on research. Some other helpful resources include Chilton repair manuals and an ALLDATA single-vehicle subscription. These resources can help you identify your vehicle’s parts and familiarize yourself with its potential problems.
Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.