Q: System too lean bank 1

asked by on July 19, 2017

My 2004 highlander does not pick up when i accelerate and at a constant speed the gear changes all times from 4 to 3 or 2 and so on. I changed the o2 sensors and spark plugs. The car jerks while driving and the gears shift continuously. My mobile mechanic says to change the catalyst converter. The engine light is on and the reason says as bank 1 too lean.

My car has 120000 miles.
My car has an automatic transmission.

Hi There, Typically, a lean fuel condition will produce DTC code P0171, which indicates a lean fuel condition often times associated with "bank 1 or 2 too lean" as you have indicated. A number of things may cause code P0171 to be triggered. As the code indicates, this means there is a lean fuel condition which may be caused by a lack of fuel supply or in some cases, a vacuum leak. When a vacuum leak is present, this introduces an excessive amount of air into the fuel/air mixture which results in leaning out the fuel content. Other problems such as a faulty fuel pressure regulator, a faulty fuel pump, a clogged fuel filter, faulty fuel injectors, faulty oxygen sensors, or a faulty mass air flow sensor may also cause this to happen. I would suggest having a professional from YourMechanic come to your location to diagnose and inspect your vehicle.

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