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o 2 sensors

1K views 6 replies 5 participants last post by  paintdrying 
#1 ·
All the o2 sensors are the same part number for my 1999? Could the sensors be bad and not throwing a code? At 111,111 miles if they are original maybe I should go ahead and just change them(two upstream). I smell fuel, so I should assume it is running rich?
 
#2 ·
This is what I'd do.
1. hook up a scan tool and scan the PCM... if you get a code from the scan tool and your MIL light is not on; your MIL lamp is busted. You should repair the MIL lamp as well as the code(s).

But if there are no codes... and you think the O2s are the problem
1. Drive around the block and take note of the engines vibrations, feel, and performance of the motor.
2. unplug the 2 front O2s (careful hot) and drive around the block again and take notice if there is a significant difference in performance. doing this should trip the MIL(showing you the computer is doing its job) but just as important you should notice a significant reduction in engine response.
3. plug you O2s back in and use the scan tool to reset the DTCs
 
#3 ·
If you smell fuel, I would check the spider and nut kit for leaks. O2's do get weak, but if they are out of range, then

there would be a code set. Do an oil change to see if the oil is fuel contaminated.

Bob
 
#4 ·
O2's can throw a code and not light the MIL. My wife had a slow functioning O2 code and no MIL. O2's get slow over time or they just simply die/break.

With the raw fuel, it could be a component of a bad set of O2 sensors, but likely it's a problem with the van mechanically. I'd want to have the van scanned with at least something that can see live data to see if the O2's are working and what the Fuel trims ( the values behind the STFT and LTFT on the scanner ) Could be that you have a leaky nut kit, pressure regulator...or just very rich fuel trim cause by faulty sensors.

However, since the van has 2 sensors, they'd have to have both gone out at the same time to not throw a code.
 
#5 ·
Yes, they are all the same and yes, they can be failing without throwing a code.

Generally, they last up to 120,000 miles. Usually, the post-cat O2 sensor isn't an issue; it's the 2 pre-cat sensors. In my case, it was the driver's side pre-cat sensor and the post-cat sensor. I used a scan tool to monitor the output and the codes. Once I replaced them, output went to normal and codes cleared.
 
#6 ·
Ok... Obd2 GM (and EPA) protocol triggers a MIL (malfunction indicator lamp) light if there is an active TC (trouble code)... no exception. If the trouble code is active (via a scan tool) and there is no MIL lamp then the lamp is out and needs to be fixed. I don't know the circumstances of the problem but a lot of people just keep driving when the MIL is on and like any light it can and will eventually burn out.

With any scan tool worth buying or borrowing you can look at past DTCs (diagnostic trouble codes). When connected with a scan tool pending/past TCs will be displayed e.g. O2 B1S1 low, O2 B2S2 high, or O2 failure.The computer PCM does not get confused or not recognize these problems it only registers them for your convenience and to be fixed. This means the MIL can go on and off sometimes without you noticing but the PCM will pick it up and tell you (via a SCAN TOOL). If the problem is so insignificant that the PCM doesn't pick up the problem then it's not worth investigating. Its electricity not magic .

There is only 3 exceptions to this... If you modified your PCM (reprogrammed) to act in a different way than the federal government EPA has regulated for all vehicles post 1995 then yes it could be failing O2 without an MIL. Else if there's a catastrophic FLUKE almost impossible failure in the binary of the computer/PCM . Or the rarest malfunctioning sensor that malfunctions the correct signal to the computer.

There are so many sensors on a modern engine that if the computer can't tell you whats wrong it might no be worth fixing... It could just be a fuel leak, or you need to do a Crank position relearn, a bad injector, maybe a faulty TPS or MAP, a screw loose, faulty EGR.

Regardless hook up a scan tool and take the guess out of the equation or post more information. :D
 
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