3 exhaust codes on FJ Cruiser

C

Chasitek

TJ Enthusiast
Supporting Member
Joined
Feb 19, 2018
Messages
657
Location
Chapel Hill, NC, USA
Not sure where to put this thread but my girlfriend recently got an Fj because she couldn't afford a JK. lol, I know that's not the answer. I tried to convince her to get a TJ but she says they're too old. Anyway, the Fj forum is crap so I'm going to ask here. I'm getting 3 codes. A P0420 (Catalyst system efficiency below threshold), P0171 (Bank 1 too lean) and a P0172 (Bank 1 too rich). How can it be too rich and too lean at the same time? I cleaned the MAF and it didn't make a difference, looked for Vacuum leaks but couldn't find any, gonna look some more tomorrow. Should I replace the MAF? O2 sensors? or cat? any other ideas as to what could cause a lean and rich code at the same time? Thanks for any help.
 
Last edited:
Yep, she should have got a tj, but I’m sure she’ll like her fj a lot. Lot of information out there if you google fj + pre cats and/or your codes, some of these might help and there are many more. Best of luck and I’m sure your fj questions are always welcome I’ve found a lot of help here.

https://www.fjcruiserforums.com/for...bad-kitty-replacing-bad-cat-upgrade-time.html

https://www.fjcruiserforums.com/for...2-warning-lights-bad-catalytic-converter.html

https://www.fjcruiserforums.com/for.../118951-catalytic-converters-temperature.html

https://www.fjcruiserforums.com/forums/maintenance-tech/562825-single-p0420-code-thrown.html
 
  • Like
Reactions: Chris
1515art said:
Yep, she should have got a tj, but I’m sure she’ll like her fj a lot. Lot of information out there if you google fj + pre cats and/or your codes, some of these might help and there are many more. Best of luck and I’m sure your fj questions are always welcome I’ve found a lot of help here.

https://www.fjcruiserforums.com/for...bad-kitty-replacing-bad-cat-upgrade-time.html

https://www.fjcruiserforums.com/for...2-warning-lights-bad-catalytic-converter.html

https://www.fjcruiserforums.com/for.../118951-catalytic-converters-temperature.html

https://www.fjcruiserforums.com/forums/maintenance-tech/562825-single-p0420-code-thrown.html
Click to expand...
I've looked it up already. I know how to replace everything and know most of the possibilities, I just needed some ideas on possible issues and how the same side can be lean and rich. Not many posts out there on a definitive fix for the same codes, just possible fixes.
Chris said:
If it were me, I'd be replacing the O2 sensors to start with.
Click to expand...
I just replaced the upstream one an hours ago so tomorrow i'm gonna get a scanner to read the live data. I'll reset the codes and see what pops back up. A lot of people say the O2 sensor won't fix it but I couldn't find too many threads with the same codes so fingers crossed it's just the o2.
 
What year, how many miles? Like Chris said O2 was the first place to start and eliminating that I would inspect the pre cats as in reading the various threads there were failures reported with miles as low as 66K. Just went through the same things on my tj... O2, vacuum checks, exhaust flange bolts/leaks and the last and most expensive was my problem clogged pre cats. The shop checked the main cat and it was fine not clogged if caught before the pre cat dumps they are usually fine according to him.
 
1515art said:
What year, how many miles? Like Chris said O2 was the first place to start and eliminating that I would inspect the pre cats as in reading the various threads there were failures reported with miles as low as 66K. Just went through the same things on my tj... O2, vacuum checks, exhaust flange bolts/leaks and the last and most expensive was my problem clogged pre cats. The shop checked the main cat and it was fine not clogged if caught before the pre cat dumps they are usually fine according to him.
Click to expand...
2007, 132k miles. Looks as if it had exhaust work done. funny thing is it looks like it had a new cat/manifold (one piece) put on recently on the side that is throwing the codes (passenger) but the drivers side looks OEM. Has some questionable welds. I might need a new cat. Looks like it was tampered with. I'm going to look more for some vacuum leaks. I do know the seal on the intake tube is not the best however the seal part is before the MAF so it shouldn't do anything because it's before right?
 
I don’t know how sensitive the maf is but a leak ahead of mine when the tubes on my aftermarket intake separated made no difference.
 
here's the freeze frame. Cat temps look fine. Is it the fuel? the short term fuel is the only difference i see from this.

IMG_4909.PNG
 
Last edited:
Top Bottom
Back