# P0174/175 Possible Fixes???



## Oleschool (Jan 4, 2014)

I've had a few codes on my 97 Pathy since I bought it.I relocated the knock sensor to get rid of the knock sensor code and I replaced the pass side catalytic.It didn't take long until the CEL came on because of the P0174.(Lean condition Bank 1).Fixed a vacuum leak and now I have a P0175 on Bank 1 and a P0174 on Bank 2.

I'm hoping that someone else has chased a problem like this and can help point me in the right direction.My next step is to try to clean the MAF and then I'm going to replace both O2 sensors before the cats.Any suggestions?


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## smj999smj (Jan 1, 2006)

Bad catalytic converters won't cause P0174/P0175 codes. This is caused by a lean condition. It's likely not caused by the O2 sensors, as well, but not impossible. Lean codes are usually caused by a dirty/faulty MAS, low fuel pressure (weak fuel pump/restrictive fuel filter/dirty fuel injectors) or a vacuum leaks. I would first get a fuel pressure tester and check to make sure it's within specs; some auto parts stores have them in a loaner program. You can spend a lot of money on new parts that do nothing to fix a problem if you don't go through the proper diagnostic steps to fix it. A factory service manual will have the diagnostic steps; you may be able to find a downloadable version in the "knowledge base" section at NissanHelp.com or at Nico's website.


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## Oleschool (Jan 4, 2014)

Thanks for the info.I'll try the fuel filter and see if I can get my hands on a gauge to test the pump pressure.I replaced the cat because I had a P0420 code and the knock sensor because I had a P0325?I can't remember the numbers but they were specific to the parts I changed and the codes never came back once I cleared them.Unfortunately after they went away they were replaced by some new ones.(174/175)I had read that the pre cat o2 sensors were a common failure item on these trucks and since I have 300k I'm doing them as a precautionary measure. I've also read that continuous rich conditions can damage them.I checked my vacuum at idle and I have a solid 20" vac after I replaced some of the hoses.

If it is dirty injectors,is it worth while to clean them or should they be replaced?

I do have a service manual which I'm using,but it's sometimes easier to gain knowledge from someone who has been there.


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## smj999smj (Jan 1, 2006)

Bad O2 sensors will usually throw a trouble code, but at 300k, it wouldn't hurt to replace them. I usually stick with NTK or Denso O2 sensors that I get from Rockauto.com at a good price. 
If you are going to clean fuel injectors, do so using a professional injection cleaning system, like those made by 3M or BG that run the chemical through the running engine from a separate tank, like this:

http://www.handsontools.com/assets/images/7649.jpg


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## Oleschool (Jan 4, 2014)

Well,I pulled the MAF sensor and cleaned it with isopropyl alcohol and a Q-tip.It was way dirtier than it looked.I cleaned the two ground screws on the intake manifold as I've read that grounds are sometimes the cause of mystery problems.I found a hose that was not properly connected, which connects a tube at the back of the pass side valve cover to a pipe that goes under the intake plenum.I reset the codes and drove the truck for about 30 kms. They have yet to return and it feels like a different engine.I hope that this ends the problems I've been having and improves my mpg.
I'll post if the codes return.


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## Oleschool (Jan 4, 2014)

I put 120 kms on this morning and the codes haven't returned.So far so good.The truck actually has some power if you can believe that.


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## smj999smj (Jan 1, 2006)

It was probably the house you fixed that caused the problems.


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