Hi All:

I have a 97 expedition 4.6l with codes PO174 saying bank 2 was too lean, a failed HO2S21, whatever that is. Also check engine lite is on that is why I took it to autozone. The engine runs smooth at idle and high speed. I am going to check the maf but that should make the whole lean. Any idea? 100,000 miles on truck

Thank in advance
john

 

Welcome to the board!

Could just be a bad O2 sensor on bank 2. There are some great mechanics here, so they will be better able to give you some suggestions.

 

Bad o2 sensor on bank 2.

 

Welcome to the forum!

 

Bank 2 lean could be a vacuum leak or a bad injector or an exhaust leak or a bad o2 sensor. If you have over 100k on the truck replace the o2 sensors. Check the vacuum and breather hoses to make sure there is no leaks.

 

thanks everyone:

For the O2 idea. will give that a try. also have 1900 250, and a 94 aerostar awd. will post back with results.
john

 

Welcome to the forum! I get the same code on my 02 4.2 V6. If you have access to one of the tool trucks that depend on their living from the techs at the dealerships, ask him to check with the pros. I was informed it is the intake gaskets that are the problem. Especially if the code is printed on cold morning starts. My truck also runs like a top with no other codes or symptoms. 166k on the odometer. Good luck! I'm still trying to verify the condition so I can do a before and after test. Here in Las Vegas it will be December before its cold enough to throw a code.

 

thanks everyone:

I replaced the O2 sensor and reset the OBD and the chech engine lite is off.

john

 

Glad it worked out for ya!