constant code 25!!!! need a real solution! searched every thread
 

ive been a long time lurker but ive finally came across a problem i cannot solve! i have a 3vze and a few weeks ago is when i started getting a code 25 for a lean air/fuel condition. (i dont see how its running lean when im getting like 10mpg!!)

i have searched through every single thread on here about the dreaded code 25 without any luck. almost every single thread has no solution to this problem except a couple people who got lucky and replacing the o2 sensor fixed it for them.

from all the threads ive read my problem is a bit different than everyone else complaining of a code 25. unlike most people who get the code, my truck runs perfect with the code. almost every thread ive read with people who had a code 25, their truck also was not running perfect...or people had both code 25 and 26.

the code pops up after every 2 starts and then i usually reset the code once every day or two. here is what i have checked and replaced so far:

-brand new denso o2 sensor
-valve clearance is good
-tps adjustment is good
-new fuel filter
-no vacuum leaks? its idling at 800..
-new ngk plugs, cap, rotor, and wires
-set timing 10degrees btdc
-maybe some other things im forgetting at the moment

any one have any ideas??

thanks

66+ views and not one post... i kinda figured this code 25 problem that so many have will never be solved.

What saith The Book?

http://www.ncttora.com/fsm/1990-1995...e/diagnosi.pdf

• Engine ground bolt loose
• Open in E1 circuit
• Open in injector circuit
• Fuel line pressure (injector blockage, etc.)
• Open or short in heated oxygen sensor circuit
• Heated oxygen sensor
• Ignition system
• Engine coolant temp. sensor
• Volume air flow meter (Air intake

I've been told that a leak in the exhaust system can cause a code 25 (the air leaks in increasing the O2 in the exhaust stream at the sensor), but since this cause is not listed in The Book I'm not sure it is correct.

Since it is easy to do, I would first check the conditioned output of the O2 sensor at Vf (http://www.ncttora.com/fsm/1990-1995...e/heatedox.pdf). If you have an intermittent problem, this may help you catch it in the act.

You could check the fuel pressure, but because the truck seems to be running okay a fuel problem is more likely in a single cylinder (e.g., clogged injector).

Good Luck!

I had this problem awhile back. This pickup sits in the garage most of the time, I dont drive it much. I changed the oil the other day, it had been 14 months since I changed it last and it had 2600 miles on that oil change. It started doing what you have described in your post, but like yours, it ran fine. Checked everything you have and came up empty, just like you. I got to thinking about maybe a fuel problem, and I couldnt remember the last time I had put gas in it. I know gas doesnt keep as well as it used to so I decided to try some fuel system cleaner and a new tank of gas. As odd as it sounds, that seems to have done the trick. Make sure you get the code cleared. May not help a bit, but thats where Im at on mine. Its been a couple of months and it hasnt came back, and Ive been driving the truck more to see if it would.

It can be caused by a leak in the exhaust system. I know because it's happened on my 3VZ-E, and fixing the leak solved it. It started when I re-installed the O2 sensor, without replacing the gasket for it too. Replaced the gasket...gone.:)

BTW, mine didn't seem to run any different with or without the code either. But, since I didn't drive it more than about 25 miles with it on, I can't say for sure what affect it may have had on fuel economy/efficiency in the long run. Other than, if there was any, it didn't make a noticeable difference during that amount of driving.

yup ive read the FSM a million times...its not a intermittent problem. the problem is there and not going away at all. i have checked the entire exhaust for leaks.

ive also checked the engine grounds and coolant temp sensor. i have not checked the VAF or fuel pressure. the truck runs absolutely perfect with the code and gets 10mpg if that. i just dont get it how its running lean!!

could be a injector BUT in my 15 years of auto mechanics i have never once seen a clogged or bad injector.

new gasket on my new o2...there just isnt any exhaust leaks that i can find..

i did however replace the stock air box/filter with a cone filter.. ?

daily bump

I feel your pain buddy. I recently went through this ordeal. Ended up being that the wire from my O2 to the computer was somehow damaged along the way. Check the signal... it's described how to check it in the FSM using an analog multimeter. After it was fixed my truck went from getting 15mpg on the highway to 19+ mpg! Still monitoring my city mileage, but I'm hoping it will be around 14-15mpg.

i havent checked the signal but did fix the wire where it was damaged at near the o2 sensor where it got burnt on the exhaust...i traced the wire all the way to the engine bay and it was all in the factory wire looms and visually looked okay. guess ill have to get a analog meter.

I got the same problem so very curious...

there are SO MANY toyota pickup owners with the same problem...that leads me to believe there is one common problem with all of our trucks that is causing it. the problem is no one has ever figured it out yet?!

and its also mainly the v6's with this problem..

The code means that the ECU has done everything it can to enrich the fuel mixture and has run out of room for "safe" adjustment.
This leaves a few areas to concentrate on.
Leaks between the AFM and the manifold, which would result in un-metered air entering the engine. This could be vacuum leaks in any one of several hoses, a problem with the brake booster or an issue between the throttle and AFM, poor wiring between the O2 sensor and the ECU, poor grounds....
Low fuel pressure- clogged fuel filter, faulty regulator, low voltage to the fuel pump.
Faulty injectors- if they are all "plugged" or spraying inefficiently you may not get enough fuel.
Throttle position sensor- if it's not operating properly, the ECU may be expecting a certain reading from the O2 based on the throttle position but not getting it.

How do your spark plugs look? Clean with maybe a little gray "ash" look? Black? Speckled?

well im not getting any fluctuation of voltage at TE1 and E1 on the diagnostic port. i tested it just like the FSM says to and the voltage stays solid at almost 14 volts and doesnt move.

voltage at VF1 and E1 is 0.05 and doesnt move.

the FSM says the next step is to replace the o2 sensor...but i just put in a brand new NGK o2 sensor...so now what?!?!

Double check you're using the correct diagnostic ports.
For some reason, I think you might want to be using the Ox connection.

https://www.yotatech.com/attachments...00701-1008.jpg

Leaky exhaust as said above.
It's hard to diagnose but very possible and very likely.
A bad gasket or a pin hole in a weld near the O2 sensor (rotten O2 gasket).

im 100% positive im using the correct terminals. mine has a diagram on the cover just like that one.

brand new o2 with brand new gasket. there was a PIN HOLE in the weld on the exhaust pipes near the o2 but i have also welded that shut. NO exhaust leaks whatsoever.

well something strange just happened..its been TWO days now and it hasnt come on. for the past month or so i would reset the codes every single day because the CEL pops on every single day...maybe it fixed itself ?? doubt it..

same boat, after reset mine will stay off during my commute to work (55 miles), typically will come on right before I get to work or 10 miles after I leave. Stayed off for two whole days and then came on again.

Just shipped my fuel injectors to be cleaned/tested, code 25 has been driving me nuts for the past six months.

i just dont think its the injectors..ive seen many people have them cleaned and even replaced with new ones with no luck.. in my 15 years of mechanics i have never seen or heard of a bad or clogged injector. but who knows. keep me posted!

if theyre clogged that would mean it would run like ˟˟˟˟ or at least stumble here or there sometimes..it runs PERFECT all the time! i dont get it.

i think something stupid is making the ecu THINK its running lean and needing more fuel. it adds as much fuel as it can and when it cant add anymore it throws the code. thats why my gas mileage so damn bad..its like 10 or less miles per gallon!