How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Matt Your Own Question
Matt, Mechanical Engineer
Category: Toyota
Satisfied Customers: 21602
Experience:  BEng, Repaired my own cars and others for 20 years, worked in Formula 1 for 10 years
Type Your Toyota Question Here...
Matt is online now
A new question is answered every 9 seconds

My 06 Corolla has the p0171 engine running too lean code.

Customer Question

My 06 Corolla has the p0171 engine running too lean code. I've replaced the MAF, AF ratio sensor, intake manifold and throttle body gasket. Also plugs and air filter. I've smoke tested it and can't find a vacuum leak. Car runs fine just poor mpg
Submitted: 10 months ago.
Category: Toyota
Expert:  Matt replied 10 months ago.


This sounds like a lack of fuel and could be a lack of fuel pressure from the electrical pump at the tank.

1st thing to try is to remove the fuel filler cap and then flick the ignition on whilst listening for the brief ‘buzz’ of the pump

If the connections to the pump are corroded or damaged then the pump could stop at any time or could not be running at full speed. Check that its relay switches in and out and the relay contacts are clean and bright – replace the relay if in any doubt and do the same for the fuse,

Ideally measure the pressure at the injector rail (should usually be around 3Bar / 45psi +) and if this is low check the pump as described and also consider changing the fuel filter as if this partially blocked this too will reduce pressure.

Customer: replied 10 months ago.
How do I check the fuel pressure? There is no schrader valve
Expert:  Matt replied 10 months ago.


in that case then you need to plumb the gauge into where the fuel line is fitted onto the end of the injector rail

Customer: replied 10 months ago.
I'm getting 11.35 v at the pump. I checked the relays and fuses under the hood and I'm getting 12.4v
Expert:  Matt replied 10 months ago.


ok if you have a voltage drop to the pump then its very likely not running as it should

try running a fresh wire directly to the pump from the battery to see if this fixes things

if it does then I'd consider making the new wiring permanent and splice it into the original exit socket on the relay , ensuring that you cut the original wire

Expert:  Matt replied 9 months ago.


do you still need help?

Bear in mind that the site takes a deposit from you at the beginning and this is held by the site until you rate my answer at which point the cash is split between the site and the expert. I am only paid for my work on this question if you rate my answer, using the star system at the top of the screen. Please do not forget! Thank you