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.

Was this answer helpful?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Very tight steering - 2006 Toyota Sienna

Hi there. When it comes to the steering, look at all of the steering components. Look at the outer tie rod ends and see if the boots are split. Do a dry park steering test. To do this, park the...

The engine comes close to shutting off while idling

This is a sign of a dirty or failing idle air control valve. The idle air control valve monitors the air intake as it is mixed with fuel prior to being injected into the motor at low speeds or at...

My car thinks the trunk is always open

This condition is likely caused by the door latch not recognizing that the door is closed. This could be due to mis-alignment of the door, a faulty latch, or a faulty striker. Another possible cause is the improper closing/latching of...

Related articles

A Buyer’s Guide to the 2012 Toyota Tacoma
Available Available in regular cab, access cab, double cab, and Xtracab versions, the 2012 Toyota Tacoma is Toyota’s answer to all of your compact pickup truck needs. In fact, Toyota has outsold both Ford and GM models, and the Tacoma...
2012 Toyota Tacoma vs. 2012 Nissan Frontier: Which One Should I Buy?
The smaller truck category includes those vehicles for men (and women!) who just want to scoot around town but who are opposed to driving a small car and just prefer a truck. These relatively fuel-efficient vehicles offer little in the...
The Best Used Cars to Buy If Safety is #1
Maybe Maybe you’re a parent buying the first car for your teenager, or perhaps you’re a new parent and the safety of your little one is of the utmost importance. Or perhaps you're a safety-minded individual looking to make a...