skytrain4

1992 Lexus LS400 with 106000 miles.

I know this subject has been worn out, beat to death, and a fork stuck it in, but....

My code 25 problem has a twist. The CEL comes on for awhile, then goes off. It is not 'blinking' on and off. There is no pattern whatsoever. It has nothing to do with the outside temperature, or how long the car has been running, or anything. It is completely random.

The first time it came on last month, I jumpered the pins and got a Code 25. I disconnected the battery, which turned off the check engine light. After a few miles, it came back on. But, before I got it back home, the light went out again. It's been doing this for over a month.

I thought that once it received an error, the CEL stayed on until it is cleared. I checked the intake manifold lines for a possible leak but everything looks and sounds okay. I visually inspected the connections to the front main O2 sensors. They are on properly. I sprayed PB Blaster on the O2 sensors and connectors yesterday to loosen them up. This week, I'm going to pull the O2 sensors, clean them, and re-install them. It's the least expensive way first. Than, I'll order the Walker universal O2 sensors as per Earl!'s website. BTW, www.lexls.com is the Mac-Daddy!!!!!

I changed all the fluids and oils in November 2004, but that's all I've done. The CEL didn't come on until a month later.

Does anyone know why the CEL would randomly go on and off?

SharpLS-96

Code 25 is an "Air–Fuel Ratio Lean Malfunction"

skytrain4

I know that. Everything I've read on this board says to replace the front O2 sensors when you have a Code 25 Air-Fuel Ratio Lean Malfunction. I'm just not so quick to jump on that when the problem seems to be intermittent. I was hoping someone else has seen this intermittent code 25 problem.

SharpLS-96

The front O2 sensors are usually the culprit but good luck in your endeavor.

lorenzo816

With OBDI sometime the codes are a clue as to what is wrong, and not the answer itself.

With OBDII the code usually is the answer.

Get an ohm meter and check the terminals on the O2 sensor and see if they are in the 5 - 6 range. If so you're good. If not you need to replace them. (there is also a way to find out if the sensors are bad by doing a lengthy rpm and flashing test by connecting to the OBD connection, but you need two people and its a pain....also determines if your ECU is bad, unlikely though)
See diagram below.


1990-1994 LS400

Note: I have replaced sensors before with non-OEM or non denso parts and I still had issues. I backprobed the connection with the car running and the difference between a non-oem and an aftermarket part was way off (mainly Bosch - borg-warner etc etc). The voltage and ampeires are wrong going back to the connection. So good luck, you might be okay with whaetver brand you buy. Or you may not be.

The signals going back to the ECU need to be exact or else it eats gas or doesn't eat enough.
I have two codes right now 25 + 26, but I tested the right main sensor, and no heater signal. So i'm placing bets that this is the issue. And I'm getting ****ty gas mileage. One time (at bandcamp) I was getting an Air flow meter code and a right main sensor code. I replaced the sensor and the AFM code dissapeared.

From my experience the sensors from Lexus are like 200 - 250 dollars, I found some non-OEM at advance for 150 and Even better go to : oxygensensors.com
or
sensors

And get a Denso for 80 - 100 bucks!

lorenzo816

by the way...

I knew it was the right side because I already replaced both of the sensors on the left side with denso parts.

I forgot to add that.

hyperopt

[QUOTE=skytrain4]1992 Lexus LS400 with 106000 miles.

My code 25 problem has a twist. The CEL comes on for awhile, then goes off. It is not 'blinking' on and off. There is no pattern whatsoever. It has nothing to do with the outside temperature, or how long the car has been running, or anything. It is completely random.
/QUOTE]

The sensor is going in and out of specs, another words, it is dying.

lorenzo816

Also with OBDII you can still have a code stored in the ECU even if you haven't cleared them yet.
Not too sure if OBDI does that.
My guess is it does keep codes. So you could still probably "flash" it to see it again.
And from what HYperopt said above it could be working sometimes and not other times.

And from my experience that the CEL only flashes (without being made to by connecting Te1 + E1) when there is something really wrong.

By the way... how can you clean an O2? Never heard of that one....
I thought either it works or doesn't. (It is an electrical part right?)

Lorenzo
1992 LS400 170k

skytrain4

I finally had time to check the resistance of the front O2 sensors. Yes you all were correct, that was the problem.

The left O2 sensor was 7.5 ohms, which is only 1.2 ohm out of spec. It may or may not have caused the check engine light code 25. However.........
The right O2 sensor was 801 ohms, which is 794.7 ohms over max spec. I'm thinking it caused the check engine light to come on. It was toast.

I replaced both sensors with Denso oems and the check engine light is off. The used O2 sensors cost $50 each from a salvage yard. They both read 6.0 ohms exactly.

The gas mileage improved immediately.

lorenzo816

I recently had another one finally go bad.

This time it didn't unscrew succussfully.
Took a chunk of inside the manifold hole and gouged some threads on the other side of that mark.

Had to wait a month before the tap and repair kit came.
If anyone else has issues with this: GOOD LUCK!
(Tap size is 18mm x 1.5)

Because either you can reach the hole and fit the tools in there to repair the threads or you can't and you have to take off the manifold. (Yeah Right?!)

I'm tellling you... if some threads go bad on a sensor hole.... its way too much work for a little job.
I got lucky and had just enough room to get a socket behind the tap and get it straight to tear into the manifold. You only get one chance Kids.

Hope this helps fellas.


Lorenzo
92 LS400 173k

skytrain4

Before I tackle any job involving unscrewing anything, I spray it with PB Blaster hours or sometimes days before I do the job. I rarely have a problem.

I hosed down the front oxygen sensors a week before I replaced them. They unscrewed so easily that I wondered if they were torqued down to start with, but I know they were.

PB Blaster is the answer everytime.

azari

how much does it cost to replace an O2 sensor?

lorenzo816

OxygenSensors.com

Buy Denso for your Lex.

skytrain4

The oem Denso are about $95 each, and are easy to install. Use PB Blaster to loosen the old ones before you try to inscrew them, or you will turn a 30 minute job into a nightmare.

uscelsior

been there done that.........in the future if you want to reset the computer just go up under the hood and pull out the EFI fuse for about 5minutes and put it back.....it will reset check engine light but if you haven't fixed the problem it will come back on.