New O2 sensor - CEL is back on after 300kms

I have an 03 XtraCab Tacoma with 70,000+kms on it. The Air Fuel Mixture sensor died recently which made the CEL light up, so I bought a new one off ebay. It is a Denso brand which is apparently the brand used by Toyota. When I had the code read prior, the CEL no longer appeared.

So once the new sensor was installed, the CEL remained off which was great but after 300kms it came on again. Just for kicks, I disconnected the battery to reset it and reconnected. The light has remained off now for about 50kms. My question is would a problem still exist despite the CEL not displaying as a result of the reset I did? or is it safe to assume there isn't a problem currently.

Thanks

Reply to
Brad P
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50 km may not be long enough to complete the drive cycle. What made you think the original sensor was bad? Any particular code? The PCM determines the sensor is bad if it doesn't switch properly in response ot engine changes.

Ed

Reply to
C. E. White

The computer's logic demands that the malfunction occur on two consecutive drive cycles. There is an very specific definition of drive cycle. It's not just start the engine, warm it up a little and turn it off. You may not have completed two drive cycles yet. Also, the problem may only occur under certain conditions which may not have occurred twice in a row. You also don't know that the code that was set is an O2 sensor code. You really need to know what code is being set. Autozone will read it for free. Once you know the code, then you really need a scan tool to diagnose the problem. An O2 sensor code doesn't necessarily mean a bad O2 sensor. The scan tool can display O2 sensor behavior, fuel trim etc. which is critical to observe in order to get to the root cause of the problem. Good luck. Al

Reply to
al

The computer's logic demands that the malfunction occur on two consecutive drive cycles. There is an very specific definition of drive cycle. It's not just start the engine, warm it up a little and turn it off. You may not have completed two drive cycles yet. Also, the problem may only occur under certain conditions which may not have occurred twice in a row. You also don't know that the code that was set is an O2 sensor code. You really need to know what code is being set. Autozone will read it for free. Once you know the code, then you really need a scan tool to diagnose the problem. An O2 sensor code doesn't necessarily mean a bad O2 sensor. The scan tool can display O2 sensor behavior, fuel trim etc. which is critical to observe in order to get to the root cause of the problem. Good luck. Al

I didn't have the code read second time around, only the first time the light came on. The mechanic said it was the O2 sensor, Bank 1. The only symptoms I experienced at the time was a rough idle at one point and bad gas mileage on the highway.

Thanks for the clarification guys.

Reply to
Brad P

The oxygen sensor is usually the victim and not the villain. Unless you identify the problem as the sensor heater burnt out or something specific to the sensor, you need to first rule out: poorly tuned engine (plugs, valve clearances, timing, vacuum/coolant leaks etc), and that there are no air leaks into the exhaust pipe upstream of the sensor. Then you need to verify that the ECU is working properly (that the signal is getting through the wires), and only then can you really point to the sensor. Many mechanics merely axe the messenger.

Many local parts stores, at least in the US, will offer OBD-II reader service for free. They'll clear the codes too. You need to make sure the codes (including hidden ones in memory) are cleared after engine component replacement. Ask for the code and post it here.

Reply to
johngdole

Why do you mess around with a stone axe and hammer when working on your truck?

AutoZone will pull the codes free of charge using a scan tool tha tis specifically meant for the job. The scan tool will reset the codes for you too. You do not have to unplug the battery, then deal with programming the radio again.

Pull the codes with the scan tool, and know that you are actually woriking on the right stuff. You can leave the gas cap loose and get a Check Engine light as a result.

Reply to
Jeff Strickland

We don't have AutoZone here in Newfoundland.

Reply to
Brad P

I booked an appt with DoWal as they can do a scan for $20, but now my CEL went off on its own yesterday as I didn't touch anything this time. So I'm not sure now if they'll be able to determine anything.

Reply to
Brad P

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