My CEL just came on this week and I'm reading a code 12 and a code 51. i just did maint that included pulling the batt cable a couple weeks ago so that explains the 12...

I searched and saw that others who had the code 51 also had rough idle or other symptoms to point at O2 or MAP sensors but mine is still running just fine. Smooth idle and no hesitations... I'm in the middle of rebuilding my other car's motor so a little too cash strapped to go blindly replacing stuff.

Thoughts?

 

The O2 sensor is doing it's job by reporting a lean condition and it has done all it can to correct it. The problem is bigger than it can handle. Although it is possible that the oxygen sensor is at fault, it is quite unlikely.

And know that you do NOT have to have symptoms to set a code. The engine can be running fine; you are just out of spec as far as the OBD system goes.

What you need to do is locate the root cause of the lean condition and correct it. A lean condition can be caused by many things including a vacuum leak, bad MAP sensor, low fuel pressure, or even dirty fuel injectors.

I'd start by ensuring there are no vacuum leaks. After that, verify your fuel pressure. You should have 31 psi at idle, then disconnect the vacuum line leading to the fuel pressure regulator (be sure that line has good vacuum) and the pressure should jump to approximately 39 psi. If fuel pressure is good, I'd test the map sensor the MAP sensor; you'll need a manual and a meter. The MAP sensor is a very important sensor when it comes to fuel/air mixture. Just like the pressure regulator, be darn sure that the vacuum line leading to the MAP sensor is in good shape, especially around the end where it connects to the sensor, and that it is pulling good vacuum.

This is a process of elimination. Test your way to a solution. Never ignore any check engine light/code. Good luck and keep us updated!

 

hmm, now that I think about it the Jeep has been a little slower to start of late. Fuel pressure is probably a good place to start. Thanks!