Code P0171 - System Too Lean (Bank 1)
 

Hi. This is my first post. I have a 2000 Protege with the 1.6L DOHC engine. 60K miles. It is reporting a P0171 - System Too Lean error code. I have cleared the code once, after I did some fuel pressure testing for a different problem, and the code has reappeared. Any suggestions as to what I should investigate?

Some additional background, possibly relevant. The car has also recently acquired a hot starting problem. It cranks fine, but will not start after the engine is hot, ambient temperature is hot (it's summer here in Georgia!), and the car has been sitting for awhile. Thinking it might be some sort of vapor lock, I tested the fuel pump and regulator. The pressure at idle is 37 psi, (spec per Haynes is 29-34) is that an issue? Without vacuum the pressure goes up to 46 psi, per spec. Applying vacuum reduces the pressure, as expected. Seems to hold pressure fine when turned off. The other suggestion in the manual was to replace the air filter, which I did. Problem still occurs.

Thanks in advance!

Richard

RE: Code P0171 - System Too Lean (Bank 1)
 

Welcome to the forum rpgrayso.:)

Any driveability problems? You most probably have a soot contaminated Mass Air Flow sensor. Very common problem with the 99-2000 Protege with 1.6 engine. Even better than that is that Mazda has a warranty extension on the sensor for 7 years or 70,000 miles. Check in with a local dealer and have them look up SSP 56. That should get you a free replacement. Mazda even covers the labor to diagnose so don't let them tell you that you will need to pay for diagnosis or install labor. Might even be contributing to the hard start as the intake air thermosensor is integrated into the MAF.

RE: Code P0171 - System Too Lean (Bank 1)
 

Thanks for the lead on SSP 56. I'll definitely look into that and report back. Regarding other driveability problems -- it's my son's car and I haven't heard of any others. Starting today he's a freshman at college (no car allowed) so I guess I'll have plenty of time to bond with his car now. Step #1 will be to clear out all the trash inside the car so I'm not too embarrassed to bring it to the dealer!

Richard

RE: Code P0171 - System Too Lean (Bank 1)
 

You were absolutely right!! The dealer service department confirmed that the issue was the Mass Air Sensor. It was all covered under the SSP56...cost me $0.00! It now runs much better. On the way to the dealer I also noticed a pronounced stumble off idle -- that is now also cured. Thanks again.

Richard