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O2 sensor problems after replacement
My 2001 4runner was giving me the code for a bad upstream o2 sensor. I just did a tune up including new spark plugs, wires, ignition coils, air flow sensor and air filter. Also cleaned the throttle body. It was running great, but the check engine and VSC lights were on. So I ordered a new o2 sensor and installed it. All the dummy lights turned off like they should. I reset the computer, let it idle for 20 minutes and drove it a while. But it ran terribly! The engine kept pulsating or revving up and down constantly. So I requested a refund and ordered a new sensor from another source. Installed it and the car runs great again. However, it also caused the lights to come back on and give me the same error code I had to start with! Anyone have any solutions? At this point I am willing to live with the lights... |
:wave:
Welcome to YotaTech! What engine do you have? Do you have a scan tool? What code(s), exactly, did you get from the 4Runner? Do you know what the fuel trims are? Is the 4Runner running rich or lean according to scan data? The computer can only tell you something is "out of normal range" based on the data it receives from the electrical system. The computer cannot tell you if a certain part is bad. In other words, there is no code for "this sensor is bad". :safari: |
I have a cheap scan tool. It gives me code P1135 with the newest sensor, same as before I replaced it at all. But it didn't give me any code at all with the first sensor I installed that made the engine rev up and down. Don't know the fuel trim. Fyi, I have about 340,000 miles on this vehicle. It is the 3.4L engine. |
P1135 is for a failed heater circuit in the upstream oxygen sensor. It may not be the sensor itself but the wiring in the harness TO the sensor. Check your wiring to make sure you don’t have any chafed or linked sections. |
That's because after changing it out, the ecu needs time and some driving to relearn the air/fuel mixture signals. A more advanced scan tool can tell if the new sensor passed or not, plus it can see pending codes that have not set.
The 2nd scenario just proves the issue lies elsewhere and is likely not the sensor. However, that part does need periodic replacement. Try reading up on it's function. Once it makes sense, I think you'll have an idea where to look. 340k and well maintained or 340k and getting caught up? I agree with above. If the wiring checks look ok, but problem is still there, you may have to confirm with a multimeter. How did the old sensor look? The condition of the coating can tell a lot about what's going on above it. |
It is well maintained but getting old and well used. I've had it 11 years as my daily driver. I try to keep everything in good working order and do the usual maintenance. The old sensor was blackened and the gasket was disintegrating. The nuts crumbled off of the studs. But I cleaned it all up when I installed the new sensors and gasket. I gave the computer 2 weeks of driving to try to learn after the first sensor was installed. It never got better even though the lights went out immediately and didn't come back on until I changed the sensor again. That's what is so frustrating! It either runs terrible with no error codes or runs great with the 1135 code. |
Any suggestions on a decent affordable scanner? Also, how do I test with a multimeter? I think I read on one of the threads that I need to check the resistance and it should be somewhere around 1.5ohms. Is that even remotely correct or have I completely scrambled info in my aging brain? |
Without a wiring diagram or fsm, it be hard to pinpoint which wire for resistance, voltage, signal. I've read on other models' sensors at less than 20 ohms, so your guess is as good as mine.
Using a meter is fairly understandable. Lot of info online. Just make sure to have the component turned off whenever checking resistance. The scan tool I use is Innova and it cut out some of the guesswork. Decent ones can go above a hundred bucks or even more. Think I spent a good 200. But it saved a lot of confusion and wasted parts throwing. Maybe a good cleaning on the contacts inside the harness from the ecu. Corrosion can increase the circuit resistance. And like fierohink said, get a really good look at the wiring for anything that is suspect. And if there's a fuse for the sensor, depends on the model, also a quick rule out. Probably just dirtied up somewhere on a connection. Be good to know what you find. Good luck! Oh, worth adding, there can sometimes be a bunch of different sensor part numbers across the same model, Fed vs Cali, manual vs auto trans, so hopefully that wasn't an issue for you. |
Originally Posted by vagabond317
(Post 52400993)
My 2001 4runner was giving me the code for a bad upstream o2 sensor. I just did a tune up including new spark plugs, wires, ignition coils, air flow sensor and air filter. Also cleaned the throttle body. It was running great, but the check engine and VSC lights were on. So I ordered a new o2 sensor and installed it. All the dummy lights turned off like they should. I reset the computer, let it idle for 20 minutes and drove it a while. But it ran terribly! The engine kept pulsating or revving up and down constantly. So I requested a refund and ordered a new sensor from another source. Installed it and the car runs great again. However, it also caused the lights to come back on and give me the same error code I had to start with! Anyone have any solutions? At this point I am willing to live with the lights... Instead of buying a new one (again), you may find a friend to swap o2 sensors with and see if the problem follows the sensor. I don't know of a good way to troubleshoot these...good luck and let us know what the fix is |
Originally Posted by vagabond317
(Post 52401042)
Any suggestions on a decent affordable scanner? Also, how do I test with a multimeter? I think I read on one of the threads that I need to check the resistance and it should be somewhere around 1.5ohms. Is that even remotely correct or have I completely scrambled info in my aging brain? http://www.teamtoyota4x4.org/archivi.../afrs/insp.pdf You may not be able to read the .pdf on your phone. Use a computer with Adobe Reader if you can't. |
So I'm having an O2 sensor issue as well.
I bought a 96 4runner 5 speed 4wd Fed emissions a few months ago....it ran great, no issues. then out of nowhere I get a P0141 code. Truck still runs the same, same mileage, no odd noises or smells. Getting a CEL though, so won't pass 'emissions' testing. I haven't done any wiring mods or driven it that much to be concerned with wiring/ECU issues. Cleared the code, got a new rear Denso O2 sensor and cleaned the MAF. Code came back the next day. Same code. Does this code only indicate a bad rear 02, or something more sinister? From my reading, it only applies to the rear heater circuit of the O2 sensor. Where else should I look? Is this code saying there is no signal coming from the sensor or that the signal is out of range? Is there a good way to test it with a multimeter? Should I be concerned with the ECU? Found this to test the sensor, but no mention of what the Ohm reading should be...AND, after reading some of the FSM....appears the Ohm reading should be 11-16 ohms. |
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