2007 Brake vacuum loss with P0171 and P0174 lean codes

2007 PreRunner V6 SR5 Access Cab - so all of a sudden I noticed that braking seems to be losing power control, I assume because of a vacuum leak in or to the power brake booster. It seems somewhat intermittent in that while driving under normal conditions the brakes seem fine. But while pressing and holding the brake pedal you hear what sounds like a vacuum leak. Then, she started throwing out codes P0171 and P0174. I have read where others have had acceleration issues and eventually found that the fuel pump filter was clogged with a sandy looking substance. I haven't experienced the accel issue, just the braking issue. Can anyone tell me where to look (what area of the engine compartment and/or what hose) that would be a vacuum issue, or do you think that the power brake booster is possibly a cause.

 

Your vacuum leak should be easy to find if you can hear it from the cab...

The fuel delivery seems like it falls under the fuel pump as a good possibility.

https://www.tacomaworld.com/threads/lean-in-both-banks-p0171-and-p0174-solved.699008/

 

If your vaccum hose going to your brake booster is good then most likely you have a failed brake booster, thats most likely the cause of your p0171/174 codes as well. If the booster is bad make sure you check for brake fluid in the booster, if theres brake fluid present you will need to replace the master cylinder as well or you risk ruining the new booster.

 

Thanks Jimmyh - I will get closer to the under-dash assembly to try and locate the source of the vac leak.

Thank you as well Dm93. All my research points to the brake booster as well, though I wanted to get other opinions about it. Good intel on fluid present in it. What's your thoughts on a reman part? Or should I stick with new?

 

We've had very few problems with reman boosters at the shop, I would avoid reman master cylinders though if you can.

 

Start it, pop the hood, and spray brake cleaner or starting fluid around any possible vacuum leaks. If the idle rpm changes you've found your leak. This will not work for an internal booster leak of course.

 

It needs a booster

 

You know this how? If he's got a vacuum leak it'll affect the brakes and throw codes.

 

He says in the first post that he only hears the hissing sound when he's putting his foot on the brake pedal. The diaphragm is leaking

Remove the brake booster vacuum line and plug it with the engine running. Then try stepping on the brake pedal and see if the hissing noise is still there, I'm betting it won't be

You could also watch fuel trims on a code reader while you push on the brakes. With the vacuum line removed and capped off the trims will probably stabilize and stay close to zero. Connect the vacuum line to the booster again, start pumping the brake pedal until the hissing noise comes back, and the trims will probably try to correct and go positive

 

FIXED!!! Thanks all for the helpful suggestions. It came down to the booster. Replaced it and all is now well. Your assistance is greatly appreciated!

 

Nice! At what cost?

 

A reman booster from Advance A/P cost $210 with a core.