The exhaust system of the internal combustion engine contains a heated oxygen sensor. After the combustion process takes place and exhaust fumes come out from the engine, the heated oxygen sensor detects how much oxygen exists in the exhaust fumes.
If the engine contains more fuel than oxygen, then it will cause the heated oxygen sensor to generate a high voltage signal which gets transmitted to the powertrain control module. If there is more oxygen than fuel, then a low voltage signal is produced. This is the difference between a rich running engine and a lean running engine.
In normal circumstances, the powertrain control module would successfully manage the fuel control system to correct any rich or lean conditions in the engine. But if the powertrain control module detects any problem in managing these conditions, then it will respond with a trouble code.
When a lean system is detected, it means there is too much air in the system because of a lack of fuel. If you run a diagnostic check on the powertrain, you’ll receive trouble code P1151 if a lean condition is present and cannot be fixed. The official description of trouble code P1151 is a lack of upstream in the heated oxygen sensor. This indicates there is a lean condition in Bank 2.
The only real symptom you’ll experience from this trouble code is the Check Engine warning light activating on the dashboard. The causes of the lean condition in Bank 2 may include a bad powertrain control module, engine vacuum leak, bad fuel injector, bad mass airflow sensor, bad heated oxygen sensor in Bank 2, low fuel pressure, and high fuel pressure.
It is important to note that P1151 is a trouble code usually associated with Ford model vehicles. You may find other car manufacturers using trouble code P1151 too, but it might not mean the same thing as it does in Ford vehicles. Keep that in mind if you see this trouble code and you’re driving a Ford or another type of vehicle.
In any case, you should always bring your vehicle to a certified mechanic whenever you see the Check Engine warning light turn on. If they detect trouble code P1151 from your powertrain control module, then they will know what to do.