Code Help - P0171 and P0174
 

Check Engine Light came on in my 2000 Jaguar XJ8 with an amber restricted performance light. Engine light has been on a couple weeks and the restricted performance warning comes on every once in a while during my drive – I drive 70 miles to and from work. Have noticed a kind of bump in acceleration at high speeds (don’t know technical language, sorry).

Autozone read the codes as follows:

P0111
Unknown – it would not list info for a Jag

P0171
The powertrain control module uses the O2 sensor to calculate the air/fuel ratio of the engine. The computer has recognized a rich or lean condition on one engine bank only.

P0174
The ECM has detected rich or lean air/fuel ratio condition on bank two.

Probable Causes for P0171 and P0174 said:
“If bank one and two codes set together suspect fuel pressure or MAF Sensor."

I used a fuel injector cleaner recently and the engine light clicked off for about a day. What could be the problem here? Any help is much appreciated. Thanks!

-Stacey

RE: Code Help - P0171 and P0174
 

If you can find a shop with an Autologic they can determine if the O2 sensors are opening and closing.

RE: Code Help - P0171 and P0174
 

either you have a vacuum leak or needs a MAF sensor

RE: Code Help - P0171 and P0174
 

jag_genius - in your opinion, its more likely to be the MAF sensor than the O2 sensor? that is not a cheap part for me, is there any way to check whether it is working properly orare the diagnostic codes clearly tellin me, hey its not working? (i am tryin to get the prob fixed as cheap as possible and as a do it yourself) -- thanks!

RE: Code Help - P0171 and P0174
 

P0111 - Intake Air Temperature Circuit Range/Performance Problem.

RE: Code Help - P0171 and P0174
 

It is most likely the MAF. Not related to O2 sensors at all.
If no vacuum leaks are evident, the MAF would be best thing to change. Also has combined MAF and IAT on your car.

RE: Code Help - P0171 and P0174
 

This is all good help, thanks. I will try to fix the prob this weekend. Thanks again.

RE: Code Help - P0171 and P0174
 

yeah .. if you dont hear any hissing or leaking.. then throw a MAF sensor in.. shud do the job

False codes P0171 and P0178....solved for free
 

My 2005 XJ8 drives perfectly after only 72000 miles, but throws the two 'lean mixture in bank ' codes. I didn't believe them. I started on a fixit trail, by replacing the MAF sensor. No difference, just a waste of money. Before exploring the fuel filter, the O2 sensors and all the expensive solutions, the problem has gone away. My conclusion: Its the ethanol in the fuel. Now that gas prices have fallen so drastically it is no longer economic to add up to 10% ethanol, so I am now driving on high-octane pure gasoline.


The other useful tip is to reset the ECU by disconnecting the + and - battery cables, and connect them into a closed loop (Not connected to either battery terminal).
Turn on the ignition and all lights...nothing comes on, of course, but it removes all static from the circuit. Hold for maybe 4 minutes. The reconnect the battery cables to the battery terminals.

It won't be that.

Try investigated fuel trims (LTFTs).

There are zillions of posts about these codes...... worth reading them.

I see fuel pressure on the suspect list, would that be to much fuel or not enough fuel or both. my fuel pressure resister yesterday at 59psi today at 70psi. Would this be my problem?