UPDATE ON LAST PAGE!!!

I swapped out my main o2 sensors about 4 months ago, hoping it'll help me get back my old gas mileage, but it didn't. Anyways, today on my way back home, I get a check engine light, so I did the manual way of checking for codes, connect TE1 & E1 and count the blinks the CEL makes. It gives me code 28 which is main o2 sensors. I would expect the sub o2 to go bad since I haven't changed those. But what do y'all think is going on here? Is there anything else I need to check? I'm pretty sure the plugs were connected right and the o2 sensors were pretty tight on the bung, only thing I can think of is the exhaust melting the wires?

Sometimes it seems, whenever you get something done, you get twice a set back. Ugh...

 

Please move to correct forums.

I think you change them out and reset the codes. Drive it for a bit and see what happens.

 

are you sure you got the right replacements, if you did I would try resetting the ecu and see if it comes back sometimes its as simple as that. melted wire is always possible.

 

Sorry, forgot.

It's just getting a CEL after 4 months? But yeah, I double checked the part number, it is the right one. Ugh, I hate going under the car on a summer day...

 

So funny I just change my O2 sensors on my 92 SC300 Monday my female & male connector mates were half melted together on the closest O2 sensors to the firewall, so its definitely a possibility. Heat from manifold. I painted my manifold with Dupli Color Engine enamel to combat the heat then tied my O2 wire to prevent anymore contact with manifold.

 

Update guys; so I just had both main O2 sensors replaced under warranty and did an entire ignition system tune-up. Spark plugs, spark plug wires, distributor rotors and caps, and main and sub O2 sensors. Did oil change with it, and Seafoam. Cleaned the air intake filter. Y'know, the whole shebang. And after all that I'm still getting Code 28.

And it actually added a couple more, Code 24 & 31; which points to the MAF sensor. A little background on the MAF sensor, I got it not more than a year ago from Gazi, as a replacement in hopes of fixing my gas mileage issue. I still have my original MAF sensor which I'm gonna try out later and see if it fixes the other codes, just not sure if it has anything to do with Code 28 so I'm letting anyone who can help me know. And yes, I already reset the ECU through the EFI fuse.

After owning this car for 3 years, I know better now than to loosing my cool. I just hope somebody can guide me in the right direction to fix this issue. Thanks in advance.

 

alot of times o2 codes come up that are related to the maf, if you have your old maf its worth swapping out as a test. I would expect a lean misfire code with a really bad maf though so its a bit puzzling, but odb1 codes rarely make all that much sense you will have to do some experimentation I would start with that.

 

OBD1 codes are funny like this sometimes. I got a knock sensor code once and then the car died a few times. I replaced the fuel pump and did the 12v mod on the relay and the code went away and car ran fine.

Then another time I got the speed sensor code. I lived with that for a while then my car died on me a few times at idle. I cleaned the IACV and TB but the codes were still there after reset. I replaced the MAF and reset. All of the codes went away and never came back.

Luckily enough it's been about a year or more without any codes.

 

Thanks for the reply guys. I just swapped the old MAF back. First startup didn't have CEL. Not sure if this makes sense, but I noticed right from the start that the CEL doesn't turn on until the car is halfway to the normal temp? Any thoughts? Now that the engine is warm again the CEL is back on. Smh

 

these engines can be scary , mechanically they last forever but with all the sensors and nick nacks they can be so hard to diagnose.

Im starting to get HORRIBLE gas mileage now and the car is stalling once in a while on idle, this will be the 3rd or 4th time im having engine issues in as many years.

the fact that you did a full tune up and o2 sensor swap and your still getting codes is a tough one, hows your gas mileage since the overhaul

 

I'm about to find out. I've got my fingers crossed. But I used to get 13-15mpg city driving prior to tune-up and 25mpg highway. That's what's got me beating my head, I just spent $500+ on OEM parts, and still I get the same code, plus another 2, LOL. I can spend another $300+ on a refurbished MAF sensor, but I wanna make sure I'm doing the right decision.

 

Forgot to add, I also did Seafoam yesterday when I did the oil change.

 

I didn't wanna get back here until I have checked the resistance and ground for the MAF sensors, and it's taking long 'cause my voltmeter was borrowed from me and haven't been returned. I have been doing a lot, and I mean a lot, of reading here and there. I have a feeling it's not the MAF sensor, it could be a wire that got cut (or chewed up by a rat) somewhere. It could be the ECTS (Electronic Coolant Temperature Sensor); I already replaced it with a Duralast one from AutoZone, although I'm sceptic about it 'cause I've read in the LS forums that some people have had bad experience with it, as to how it is connected to the codes I'm getting I'm not sure, but I've read a handful of threads from there and people usually suggest changing those out first. I just bought another MAF sensor from a local guy, now I have 3 MAF sensors and I am still getting the same CEL codes. I've never had any kind of engine issues whatsoever. It never stalled on me, not once. Idle has always been perfect, never stuttered or bogged down. Just wondering if there's anybody else out there who have experienced this? Again, codes I'm getting are;

Code 24 - Intake Air Temperature Sensor Circuit
Code 28 - Main Oxygen Sensor Circuit
Code 31 - Air Flow Meter Circuit

 

Update: I was able to get the code 24 & 31 cleared out. I really have no idea how I did it exactly, I just checked and took apart all the spark plug wires connections to the spark plugs and distributor caps and rotors, cleaned the honeycomb grille for the intake manifold, and cleaned the battery terminal connections and cleaned the 2 year old PCV valve. Then put everything back together and voila! The codes 24 & 31 are gone.

Now, I'm stuck with the code 28 which I've been getting right from the start. I searched a lot, also through Lextreme, and everything I see with the exact same issue wasn't a completed thread. It seems to be a common issue; code 28, replaces o2 sensor for right bank, gets code 28 again after a few months.... One thread I saw, the guy even tried switching the 2 sensors, and still get the code 28. Again, mine is brand new OEM Denso, it's been second time to be replaced, I did an entire ignition system tune-up with this. Car is running perfectly normal, no idle issues, no misfire, no stutter, no hesitation, runs very smooth, runs just a little lean compared to before i did the tune-up.

I'm thinking about cleaning up the idle control valve, but a little scared to touch it since there's nothing wrong with it. My TPS was just adjusted to specs not too long ago, way before I get CEL. I did the 12 volt mod a long time ago too. Please if there's anybody who knows, let me know. Thanks.

 

Nobody buddy?