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Q: Error codes P0171 and P0374

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I used the OBD II / EOBD CODE READER and found the following code (4 error codes) P0171 System too lean Bank 1, P0374 Timing Reference Hig n Resolution Signal A No Pulses, P0171 System too lean Bank 1, P0374 Timing Reference Hig n Resolution Signal A No Pulses,

The same code reader gave me RPM(rpm): 705.50 while the engine was running but the gear was in Parked position.

I don’t feel anything while driving the 2006 Ford Five hundred SEL (I don’t have much knowledge about vehicles), It accelerates well and goes easily to 40miles per hour when given the acceleration (I have not tried beyond 40 miles/hr in order to avoid any damage, as I bought it recently and want to repair it before use) the odometer reads about 200,000 miles, I showed to a local mechanic he said the gear is either in 2nd or 3rd (limp mode) after a short test drive, which made me little worried, what can be the possible reasons of this errors and what should I do to make it a smooth running vehicle?

My car has 200000 miles.
My car has an automatic transmission.

A: Hello. These issues can be caused by a few ...

Hello. These issues can be caused by a few things. From the codes it sounds like there may be an issue with the fuel system. It may also be an issue with the air intake system allowing too much air into the engine. The main code here is the lean code meaning too much air or too little fuel. I usually start by checking the fuel trim reading are in the computer to see what is going on. This would tell me if I am looking at a fuel system problem or possibly a sensor that is reading wrong. If these codes are present, the computer can also put the vehicle into limp mode which would explain why it is shifting like this. If you want to have these engine codes scoped, consider YourMechanic, as a certified technician can come to you to diagnose the Check Engine Light and pinpoint the underlying repairs that are needed.

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