Car Engine Light just came on?

Hi, my car, ‘99 ford escort,’ engine light just came on when I started the car. I took it to autozone for one of those checks with the machine thingy. The code was PO171 bank 1 system 2 lead. The girl at autozone told me that I may need a oxygen sensor. How much will this cost? What is a bank 1? What do I say when I go to the repair shop?

A P0171 is a generic code which I think means that the car runs too lean - iow, the air/fuel mixture isn’t right. The O2 sensor makes measurements that will determine that fact so a bad o2 sensor could throw the error but is really could be a number of things.
It could for instance also be caused by a bad PCV valve or leak in that general area. That’s actually a lot simpler and less expensive to fix than an O2 sensor.
I wouldn’t just throw parts at it.

What to tell the repair shop? You need not say anything more than that your check engine light is lit. Ask for a diagnosis and an estimate of repairs.

So far you have two guesses – oxygen sensor and PCV valve. Neither repair is very expensive, but neither answer may be correct. If the mechanic suggests these repairs are in order you may proceed. If he recommends a major overhaul generating a huge bill, go elsewhere.

The P0171 is indeed that the O2 sensor is reporting a lean condition. Replacing the O2 sensor for this is often shooting the messenger.

The first thing you do is check for vacuum leaks and clean the MAF sensor. A can of MAF sensor cleaner will run you about $6 at an auto parts store. The rest is just labor. There are lots of ways you check for vacuum leaks & they can be hard to find. First the whole intake snorkel should be checked at both ends for tight connections to the throttle body & air filter housing. It should be removed and checked for splits and other damage. All visible little black bits of hose & small black bits of plastic that look like plumbing can be looked over. There is a vacuum schematic under the hood that can help. If visual inspection turns up nothing, a general routine is to feed something flammable (e.g. carb cleaner, unlit propane torch) around vacuum connections & the intake manifold. The engine will respond if you hit a leak. You can also listen carefully - a vacuum leak will hiss.

Do all of that and clean the MAF while you’re at it. Have the code cleared and see what happens.

Bank 1, btw, is the row of cylinders with cylinder #1 on it. Your car is a 4 cylinder & only has one “bank”

How many miles are on your car? Oxygen sensors have a design life of around 100K miles. So after cleaning the MAF or having it cleaned and checking for vacuum leaks, replacing the sensor makes sense if you are over that mileage…

This code is notoriously hard to fix without doing a real and proper diagnosis. It could be due to dirty injectors, weak fuel pump, clogged fuel filter, minor vacuum leak, or a dirty MAF sensor.

Have a proper diagnosis performed. It will be cheaper than throwing parts at it.

I would pull your pos batt connection and leave it off for about 2 minutes and reconnect it. This will reset your ECU. Then drive…see if it comes back…if it does…act on it. If not…keep driving…