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splitslim

Can't Reset Check Engine Light

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Hi, I have my check engine and TRAC OFF light on due to a faulty O2 sensor (code 28). During the winter I was able to reset this by disconnecting the battery for a few minutes then re-connecting it. However, last night I disconnected the battery for a few hours, reconnected it and the lights stayed on. My trip computer and radio reset, but the computer didn't for some reason.

The reason I wondering is because last night I took the sensor out to clean it, and usually when I would reset the computer using the mentioned method I would get 40-60kms before the Check Engine light popped up again. Now I have no idea if cleaning the sensor did anything.

I'll be picking up a new sensor today from Uncle Lex, but I would really still like to reset the damn thing before I installed it.

Any help would be great.

Thanks

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If it didn't turn off then there is a problem with the sensor.

Unless it is a wire problem .

did you test the wiring?

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Thanks for the reply.

I took the sensor out, cleaned it pretty well, and replaced it. I don't know how to test it, so I did not.

The weird part is, that before I took it out, I was able to reset the computer by disconnecting the negative battery cable, however the check engine light would come back after 40-60kms. Now it just stays on even after diconnecting the battery for numerous hours. I went out and bought a new sensor today, but won't be able to install it until Saturday (Leafs game tonight;-), so what I'm worried about is after I install the new sensor, do I have to reset the computer again or will it see that the sensor is new and now working?

Thanks

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it might be smth else now:) have your car checked for codes again

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Update....

I changed the right o2 sensor in front of the cat yesterday, the check engine light successfully reset, but now after 49kms it's back! :angry:

Before i changed the sensor I was getting error code 28, but now I'm getting error code 25. Do I need to change another sensor or is something wrong with the one I just put in?

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Code 25 - Air/Fuel Ratio Lean Malfunction

What confuses me is that there are already codes designated for each o2 sensor (main bank left and right, secondary bank left and right). However, everything I'm reading in the internet points to code 25 being a faulty o2 sensor. Well which one? I really don't want to replace the remaining 3 ($900 in parts here in Ontario, Canada.)

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hmmmm, now I'm reading that it could possibly be the fuel filter because I'm not getting a second code indicating a faulty o2 sensor.

thoughts?

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Maybe this will help with your Code 25 issue. This is from my 94 LS manual and is probably applies to your 91 as well. Good Luck. Keep us informed. If I can help further let me know.

Kevin

Code_25.doc

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Not sure why your Trac is off.

Most likely the Code 28 which is the "Main Heated O2 Sensor Circuit-Right"

Trouble Area:

-open or short in heater circuit of main heated o2 sensor-Right

-main heated o2 sensor(right) circuit

-main heated o2 sensor(right) voltage alternating above and below 0.45 volts.

When was the last time you changed your coolant?

Code 25 could also be the problem.

I would recommend replacing all of your o2 sensors. Yes they are expensive, but it is likely going to solve the problem. I might be able to get the 02 sensors cheaper, since I have to buy a set as well (experiencing the same problem Codes 32 and 25).

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Kevin, thanks for the document. The check engine light and trac off light came on as I said after 49 kms, at idle with the Temp gauge right in the middle. I have not flushed my coolant in a while, would this make a difference?

Question however, which sensor is the 'main heated oxygen sensor' the document is referring to? Am I right to conclude that there are 2, on the left and right, before the cat?

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Split--

I am looking at the main O2 see attached again from my 94 manual. Take a look at the graph. I have not digested this but may help. The file sizes for this site at 100 K make it a challange to size images to pass. I have more detail on the O2 sensor and can pass it to you as well.

The main sensor is front most sensor.

Kevin

main_o2.doc

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Split---

More than you everwanted to know about O2 sensors. This may be of interest to others thus my 8 scans to get this below 100 K. I have already complained.

Your all welcome.

O2_Sensor.doc

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Kevin, thanks for all the information.

So I guess since the Right main is new, the left main needs to be changed now. Could this problem possibly be a PCV valve or airfilter however?

I hate o2 sensors :P

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You have got me on this but one suggestion is to find out from your dealer which O2 sensors are the same. Since you have a new one you might swap the similar sensors and see if you get a different code. I know this is a job but it only costs you your time. Codes seem rather difficult to diagnose and solve without proper equipment.

You may have to work with your dealer or a reputable shop and pay for some diagnostic work.

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check to see if you have a rip or hole in the intake track after the maf sensor. If so the engine would run lean and also give slight acceleration problems when under full throttle especially.

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Update....

I changed the right o2 sensor in front of the cat yesterday, the check engine light successfully reset, but now after 49kms it's back!  :angry:

Before i changed the sensor I was getting error code 28, but now I'm getting error code 25.  Do I need to change another sensor or is something wrong with the one I just put in?

I guess LS400 used L/R O2 sensor to let you have 2 guns. eg if one gun is dead you won't have to hand up. But for one sensor only car, you have to repair it asap.

My 92 LS400 got check engine light last week(155K miles on it), code 25, any one have suggestion? Thanks!

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