OBD Code P0171 - system too lean (bank 1)

toyota
corolla

#1

I had the check engine light come on and the local store read the OBD code. Some preliminary research indicates that this is from too much O2 in the exhaust, and cleaning the sensor may be the best solution. Are there any risks to driving this for a while till I have money to fix it? What are things I should look out for when I take it in? Are there any other possible problems?


#2

I am suprised the “local store” did not recommend a mass airflow sensor cleaning as they sell the product and most I have seen have good instructions on the can. Suprisingly after an inital check for vacuum leaks (not likely because with todays cars there are very few potential places for vacuum leaks) and the MAF sensor cleaning next on the list is a fuel filter. You can drive but you want this fixed as this system can alert you to secondary issues but not with the light already lit. Flashing light means fix now (but it is not the same urgency as a oil can light or a overheat condition), those are stop right now.


#3

Blow $5 on a can of MAF sensor cleaner (the MAF sensor is not the O2 sensor) and spend a few minutes to clean it. See what happens. Might as well replace your air filter while you’re at it.


#4

But in the end you will need to replace the upstream oxygen sensors…This is the part that generated the CEL and they don’t last forever…


#5

I am about 6,000 miles into a MAF cleaning instigated by a P0171 on my 2004 F-150. Cleared the code by a battery disconnect and have been motoring on.


#6

Unless the O2 sensor is just doing its job.


#7

If it was the MAF, BOTH banks would be lean, not just one…When one bank throws a lean code and the other bank is fine, I suspect the o2 sensor…


#8

Its a Toyota Corolla - its only go one bank.


#9

Thanks for all the good advice. I will get right on it.


#10

OHHH snap!


#11

If the car has an intermittant shaky idle and sometimes stalls when coming to a stop clean the throttle body. There is a very good chance that is the only problem.


#12

Cleaning the wire in the MAF sensor and cleaning the carbon out of the throttle body are close but not the same, do both. The indication I use that a throttle body cleaning is called for is a slight stickyness when initally pressing the gas pedal, then it all of a sudden breaks free. This makes for jerky application of the throttle.

My F-150 obviously has two banks, my code was just for one bank but the MAF cleaning worked. I was dreading the possibility of needing an O2 sensor as the bank account was low.


#13

This kind of trouble could also be caused by a air leak in the intake or the exhaust systems. A leak in the intake after the MAF sensor or in the exhaust system before the O2 sensor. If there is over 60k miles on the sensor replacing it may solve the trouble. If you don’t find any air leaks you might try replacing the sensor.