Replace O2 Sensor And Still Get Check Engine

[Moony400]

Some help please. My '94 sc400 got the check engine and trac off light. A buddy did some test (read code) and said code 25, bad o2 sensor left bank. He orderd one $180 and I replaced it (simple to do). Still getting check engine and trac off light. The funny thing is the light never comes on till the temp gauge reaches mid way and only if I have the AC off. With the AC or climate control on, I can drive for ever without the light ever coming on or if it did only for a short time and goes back off. With the climate control off, as soon as the temp gauge reaches mid way, the light seems to come on more often. It goes away when I'm driving on the freeway, but when I slow down or come to a stop, it comes back on. The one time that it alway comes on regardless if I have the AC on or off is when I pull up to my drive or parking lot and put the car in park. The RPM lowers a little and comes the check engine light with trac off. Now at this point (while car is in park) if I turn the AC off, the RPM drops real low and goes back to normal.

My buddy suggested check the wire that plugs to the o2 sensor or replace the ECM.

Has anybody experience this or know what could be wrong? Any ideas would greatly be appreciated.

Thanks,

Moonysc400

[JamesN]

Check your ignition coil plugs. Clean it with cleaning solvents and dry it before putting it back. If still doesn't work try to take out all of the electrical plugs or sensor plugs that looks dirty and clean it. This method works for me and i hope it works for you. Other wise it could be your CAT that gone bad. Good luck.

[SKperformance]

When the car is cold the ecu is in open loop and not reading codes such as the o2 as it is still cold.

Have you tried cleanign your maf and throttlebody/intake

[Moony400]

Thanks for the reply. I will try to clean the MAF first, since it's the easiest. I did take a look at the throttle body intake when replacing the spark plugs and it looks pretty clean. The car has 102,000 miles.

JamesN, where is the ignition coil plug?

Again, thanks for the reply and info.

Moonys400

[JamesN]

There are 2 of them. One located near the thermostat and the other one located near AC compressor. See attachment, I circle it red and good luck with the trouble shoot :)

[Moony400]

JamesN, Thanks for the attachement. Also where did you get the strut tower bar and for how much?

Thanks,

MoonySC400

[DomLee]

The sticker on it says JIC. http://www.jic-magic.com/

[JamesN]

I got the JIC STB for 160 at importfan.com along time ago. But you can get yours at http://luxurymods.com/ProductList.php?CatID=14&fid=1019 . Its alittle cheaper.

[jzz30]

did you reset the computer after changing the O2?

[Moony400]

Not quite sure. I was told to disconnect the battery when replacing the O2 sensor and that would seset it. I also disconnected the battery afterward when I changed my air filter to K&N air filter. I was told by K&N support to disconnect the battery for one hour to reset the CPU. When disconnecting the battery, all I do is disconnect the negative terminal. Is that the right way to do it to have the CPU reset?

Thanks,

MoonySC400

[Moony400]

Oh, just to make sure I buy the right stuff, what kind of cleaner should I buy to clean the plugs?

Thanks,

MoonySC400

[jzz30]

yea but you only need to disconnect the battery for like 2 min. or you can disconnect the EFI fuse if you dont want to reset your radio stuff and clock.

[Moony400]

Hello, got more problems after cleaning the MAF. Now the check engine light comes on right after starting the car. Even when it's cold. What I notice now after the starting the car is sometimes the engine rev up and down like crazy and the engine would shut down. Sometimes it take four starts to make it out of my drive way. Like I said before, the check engine light only comes on after the engine is warmed up and hardly comes on when the AC is on. Now the check engine light comes on instantly. If I leave the car in park and rev up the engine to about 4000 or 5000 RPM, it forces the check engine off, but I'll notice some mis-fire in the engine. When I let off the gas pedal the check engine light comes right back. Sound like I got a big problem here. Any suggestion please or is my only option now is going into Lexus and get slap with repair bill.

Suggestion please.

MoonySC400

[Moony400]

Just checked with lexus dealer and they want $1,028.00 for a MAF sensor. Wow!

[Moony400]

Okay, need some input here. I unplugged the MAF connector and of course got the check engine light right away, but the car seems to run just fine. The car starts fine and run fine. I didn't notice any misfire or hesitation in the car. Run and accellerate good. I was driving around all weekend without a problem. Is it safe to assume the MAF is the culprit? Also for the experts, is it bad to drive the car with the MAF disconnected even though the car runs fine that way?

Thanks.

[MitchB]

The ECU will run the engine with no MAF, but not necessarily efficiently. (But not so badly either, obviously.)

Once you disconnect the MAF, the ECU defaults to maps. How did you clean the MAF? The best way is to use Electrowash spray or something similar.

[Moony400]

MitchB, thanks for the reply. I did spray the MAF with throttle boddy cleaner I got from Schucks. Is there any special cleaning that has to be done. When I pull out the MAF, all I see is a plastic rod like and sprayed with the throttle body cleaner. It didn't seem dirty at all when I pulled it out, but cleaned it any ways. Is there other components of the MAF that needs to be opened and cleaned? Also, with the car driving okay without the MAF, is it safe to assume the MAF is bad?

Thanks,

MoonySC400

[MitchB]

Well, you probably killed it with the TB cleaner, although, it may have been dying anyway. (An O2 code doesn't always mean that there's a bad O2 sensor.)

I'd be looking for a salvage yard unit.

[Moony400]

I finally figured out how to read the check engine code last night. Got code 31. Three short blink, small pause, one short blink, long pause and cycle again. Checked out code 31 in www.alldatadiy.com and it show trouble spot to be the MAF, the MAF cable to the ECM (short or open) or the ECM it self. I ordered a used MAF for $130 and we'll see if it's really the MAF.

[sha4000]

I finally figured out how to read the check engine code last night.  Got code 31.  Three short blink, small pause, one short blink, long pause and cycle again.  Checked out code 31 in www.alldatadiy.com and it show trouble spot to be the MAF, the MAF cable to the ECM (short or open) or the ECM it self.  I ordered a used MAF for $130 and we'll see if it's really the MAF.

←

that could just mean the connector wiring is not good not necesarilly the sensor itself

[Moony400]

Hope some one can give some input quickly here. I replaced the MAF with one I got from wrecking yard and still getting check engine. I read the code and still code 31. I decided to take it in to a Lexus dealer this morning and now got a call from them stating that their is something wrong with the ground wire and will require some time to replace or fix at $500. Does any one know if this is true or is the dealer trying to make some money.

[SKperformance]

You could change all the main grounds from the battery ,alternator , chassis , and other motor points.

It would cost about $30 for some good stereo power wire with gold connectors.

Since you can do simple stuff like clean the throttle body you should have no worries making the kit and installing them in about 2 hours max going very very slow.

[MitchB]

Hope some one can give some input quickly here.  I replaced the MAF with one I got from wrecking yard and still getting check engine.  I read the code and still code 31. I decided to take it in to a Lexus dealer this morning and now got a call from them stating that their is something wrong with the ground wire and will require some time to replace or fix at $500.  Does any one know if this is true or is the dealer trying to make some money.

←

Most mechanics can't use a voltmeter, much less have their service manager know what's wrong with your MAF without actually looking at the car.

Don't take it back there! Any reputable Toyota mechanic can do a good job.

Does it at least run now with the MAF installed?

[Moony400]

Hi All, I appreciated every one's input on this matter. Problem finally solved and my car is finally running without any problem or check engine light (fingers crossed).

Here's how it went down.

After do all I can, I finally took it to Lexus of Seattle, WA. Remember I took the car in with the MAF I got from a wrecking yard for $135 installed. They did the diagnose and bad ground wires that ties to the MAF and O2 sensor. $500 later, they say the check engine only comes on when the car is cold. When it reached operating temp. check engine light goes off. They did some testing on the MAF and found it to be bad. When they tap on it while the car is idling, some times it would shut the engine down. They call me up, says it going to be $1028 for a new MAF. I told them, I'm going to pick one up from a wrecking yard near by and bring it over. Went to Nix Toyota wrecking yard and pick one up for $350. Took it to Lexus, they installed it and works fine now. So after parts and labor and diagnose, it came to about $1045 (includes the first MAF from another wrecking yard).

Just glad my Lexus is now running properly.

Again, thanks for your input.

MoonySC400

[MitchB]

Yikes, that was spendy for such a "simple" problem.

Most yards do give a short warranty on their parts, even electrical parts. I'd ask them if you haven't already.