Question about 1999 Mercury Cougar

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Sensor light is on and I had it checked at Advance Auto they said it was reading lean in bank 1 and 2. What does that mean and what do I do now?

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This can get very in depth to explain,but I will do may best. the oxygen sensor in the exhaust pipes are monitoring the amount of oxygen present in the exhaust stream, when all conditions are correct the oxygen sensors will fluctuate a voltage signal to the (power train control module)between one tenth of a volt to nine tenths of a volt, the higher voltage represents a rich condition and a lower voltage represents a lean condition. when the voltage sent from the oxygen to the module continues to only sent a lower voltage signal the module realizes that the engine is running lean,(not enough fuel) and then trips the check engine light on your dash. now a lean condition can be caused by many problems, first off the most common problem I see is that a person does not keep there air cleaner element clean with ends up contaminating the mass airflow sensor,which is in the air tube between the air cleaner housing and the engine this is a sensor with wiring leading into it,(sometimes its mounted right on the air cleaner within a aluminum housing)once removed which sometime requires a taper proof torx tip tool. you will see two small wires that almost look like miniature electrical heater elements ( like a small in house heater ) these little wires get very dirty when the air filter element is not changed properly,they should be light silver if they are black or show signs of dirt,they can be cleaned using a mass airflow meter cleaner which can be obtained at a good parts not touch these wires as they are very fragile,the only approved way to clean these are to spray them with a approved mass airflow cleaner and I have taken a tooth brush and very carefully brushed the dirt and grime off them. this sensor monitors the amount off air flow coming into the engine and if the wires on this sensor are dirty,the sensor cannot accuratly monitor the air flow which will make your engine run very lean.if you do not see any signs of dirt or bulid up on this sensor, you should look for hoses that are disconnected or cracked that could cause a vacuum leak,and repair as needed. also low fuel presure would cause a lean condition. if you don"t find a consern with the mass airflow sensor and no hoses cracked or unhooked the other thing you can try is to get a can of brake cleaner (must be flammable)from a parts store and use the straw that came with the brake cleaner and very carefully spray it around under the hood at the top of the motor near the intake manifold, if you hear the engine speed increase you have found your vacuum.leak and repair as needed

Posted on Dec 29, 2010

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Bank 1 and 2 refers to the cylinders on each side of the engine.If they are reading lean, it means the air/fuel ratio is incorrect. It could be caused by the O2 sensors, but it's unusual for both sides to fault at the same time. My guess would be an air leak somewhere. Perhaps a loose or damaged vacuum hose, or air leaking into the air intake ducting somewhere between the mass airflow sensor and the throttle body.

Posted on Dec 29, 2010


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Lack of Upstream Heated Oxygen Sensor Switch Sensor Indicates Lean Bank 1
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P1131 Ford
P1131 Ford - Lack of Upstream Heated Oxygen Sensor Switch Sensor Indicates Lean Bank 1

Repair Importance Level: 3/3

Repair Difficulty Level: 2/3

Forum Code

Possible causes

- Faulty Oxygen Sensor

- Vacuum leak affecting bank 1 only

- Fuel injector problem bank 1

- Check for cylinder misfire on bank 1

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Tech notes

Though the Oxygen (O2) sensor, the Engine Control Module (ECM) has detected a lean system, which means that there is either not enough fuel or and excessive amount of air in the system. Start by checking for vacuum leaks.

When is the code detected?

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P0171 just replaced mass air flow

p0171 is system to lean ( bank 1 ). did you turn off check engine light with a scanner! if not go to auto-zone and they will erase it for free, then you can see if light stays off. There could be a vacuum leak downstream of the MAF sensor.
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