# po171



## musicfan (1 mo ago)

Hi guys have a 99 altima and have a p0171 code. I cleaned the mas sensor and worked better but light came on. Sprayed carb cleaner on the vac lines that saw and no change. Got a new gas cap nothing. I unplugged the mas wire harness and it almost died but did not then unplugged map sensor nothing. Guy work with said the mas was good and map sensor bad. I am getting bad mpg's rough idle at times and will cut off when park. Light comes on after car is warmed up. Any ideas and thanks


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## 1.8TTony (5 mo ago)

P0171 System To Lean Bank 1.

Yes a bad MAP sensor *can* cause the P0171 code to appear. However, if the MAP was bad, P0106 code would also appear and this P0106 would most certainly appear long before P0171 shows up. 

So basically, one of two things is happening: The engine is getting too much air or the engine isn't getting enough gas.

First thing I would do is ensure there are no exhaust leaks at the cylinder head/exhaust manifold gasket area. Because if exhaust can leak out past the gasket, air can also leak in past he gasket as we......which could cause P0171.

Next, thing I would do is make sure that the A/F ratio sensor and the o2 sensor are both tightly in place. These sensors are B1S1 and B1S2 respectively. If either (or both) are loose, this code can occur.

Next, inspect those sensors wire connectors. Replace if damaged or corroded.

Next, pull the PCV valve out of the valve cover and shake it. If it doesn't rattle, replace it because it may be stuck open allowing too much air to flow into the engines intake manifold resulting in the P0171 code.


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