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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / November 2004Oxygen Sensor - Is it either good or bad, or can vary from one to the other?
My 96 Chevy has check engine light burning. AutoZone code reader said rich on bank 2, which the AZ guy said generally meant Oxy sensor. I back probed the sensors on both sides with a digital voltmeter and they both operated within the same range - .1 to .9, at about the same speed. I concluded it was not the oxygen sensor. I replaced the plug wires, 2 of which had pretty low resistance, and cleared the codes. It ran for about 100 miles before the code was reset, still rich on bank 2. So now I am wondering if the oxy sensor could periodically be failing? I have checked for vacumn leaks and found none. Thanks, Libby > My 96 Chevy has check engine light burning. AutoZone code reader said > rich on bank 2, which the AZ guy said generally meant Oxy sensor. I [quoted text clipped - 8 lines] > Thanks, > Libby I wonder how many O2 sensors AZ sells because of salespeople like that... Sure, it could be a stuck O2 sensor, but it could also be many other things.. looking at the real time data stream would be helpful, esp. the fuel trim numbers. Regards, Jim You would get better qualified answers if you had posted the code they read out and if there were any other codes. Lacking an OBDII tester and knowledge of the engine you will probably money ahead taking it to a qualified mechanic with the tools to analyze it or to the dealer. Guessing and swapping parts can get very expensive. > My 96 Chevy has check engine light burning. AutoZone code reader said > rich on bank 2, which the AZ guy said generally meant Oxy sensor. I [quoted text clipped - 8 lines] > Thanks, > Libby If I wanted someone to tell me to take it to the dealer, I wouldn't have posted to this group. The code is P0175 and my question was whether the oxy sensor can periodically be bad. I tested it with a digital voltmeter, the same as many mechanics would. And I have both the knowlege and the testor. thanks to both of you for nothing. > You would get better qualified answers if you had posted the code they read > out and if there were any other codes. Lacking an OBDII tester and knowledge [quoted text clipped - 14 lines] > > Thanks, > > Libby > whether the oxy sensor can periodically be bad. Simple answer to a simple question: Yes, O2 sensors can give inaccurate readings intermittently for several reasons. DS > > whether the oxy sensor can periodically be bad. > > Simple answer to a simple question: Yes, O2 sensors can give inaccurate > readings intermittently for several reasons. > > DS they get "lazy" sometimes. they are just contaminated enough to give false readings. or the natural air vent is caked up. Chip > If I wanted someone to tell me to take it to the dealer, I wouldn't > have posted to this group. The code is P0175 and my question was > whether the oxy sensor can periodically be bad. I tested it with a Libby, an Oxygen Sensor, along with basically anything in the exhaust gasses path, (like the muffler, catalytic converter) is one of the first things to rot out on the list of things that rot out on an engine. Stainless steel exhaust has helped to reduce that, but still, these components get a lot more stress than the rest of the vehicle. You didn't mention how many miles are on this car (and I'm surprised nobody asked) well if you get 100K miles out of an O2 sensor your doing good. The only way you can test an O2 sensor is with a scan tool plugged into the scan port on the computer in your car, preferably when your driving around so you can look at it in real time, under many different engine conditions. But even many of the professionals don't do that because the 1/2 to 1 hour of labor that burns up is enough to pay for a new sensor. If you look online, you can probably get replacements cheaper than AutoZone if your willing to order them and wait a while for them to be shipped. Ted >If I wanted someone to tell me to take it to the dealer, I wouldn't >have posted to this group. The code is P0175 and my question was >whether the oxy sensor can periodically be bad. I tested it with a >digital voltmeter, the same as many mechanics would. And I have both >the knowlege and the testor. thanks to both of you for nothing. AMF, Libby.. Plonk for rudeness.... "When a legislature undertakes to proscribe the exercise of a citizen's constitutional rights it acts lawlessly and the citizen can take matters into his own hands and proceed on the basis that such a law is no law at all." - Justice William O. Douglas > My 96 Chevy has check engine light burning. AutoZone code reader said > rich on bank 2, which the AZ guy said generally meant Oxy sensor. I [quoted text clipped - 8 lines] > Thanks, > Libby If bank 2 is running rich, it is probably only something from bank 2. Since fuel rail pressure is common, and injectors could be pulsed from data of bank 2 oxygen sensor, oxygen sensor is likely culprit. That code you got means based on bank 2 oxygen sensor computer tries to adjust bank 2 injectors to what oxygen sensor is telling it. And then computer looks at how rich it is squirting bank 2 compared to a table that tells it what it should squirt at that engine load, speed, etc. This table is from a factory engine in a laboratory on a dyno. It finds that it is squirting more than it should for certain engine conditions. If you had a good OBD 2 reader it might tell you it was only rich at idle or some other condition, ie a 97 ford ranger I worked on had a lean engine bank 1 and 2 code and from scanner data it showed high fuel trims (adding too much fuel compared to table) only around idle. It turned out to be a vacuum leak. But you have a rich code only on 1 bank. Rather unusual since too high fuel pressure in rail would probably cause both banks (oxygen sensors) to indicate a rich code. I would assume banks are controlled seperately to allow seperate fuel adjustments on both banks. So your code shows computer has to subtract fuel from bank 2 under certain conditions. Usually it is oxygen sensor biaised high, which I have seen a few times. This means oxygen sensor tells computer it is richer than it should be. Usually oxygen sensor will go from 0.9 to only maybe 0.4 or something like that so computer has to try harder to get sensor to show lean and so mixture averages leaner than table. It is much more common for oxygen sensor to deteriorate lean bias. My advice is to try another oxygen sensor, or switch sensors if possible and see if code travels to bank 1. Also while using a meter can give you an idea of oxygen sensor condition nothing beats a digital oscilloscope, for instance I saw a funny shaped wave once but on a digital meter it would show good variance and high and low. Also maybe if a 4 wire sensor you can probe signal wire and ground wire. Maybe oxygen sensor ground is bad which would give a rich bias. 4 wire sensors usually have a oxygen sensor signal wire, signal ground wire, a heater voltage wire and a heater ground wire. So maybe the oxy ground wire back to computer has a high resistance. > > My 96 Chevy has check engine light burning. AutoZone code reader said > > rich on bank 2, which the AZ guy said generally meant Oxy sensor. I [quoted text clipped - 45 lines] > wire, a heater voltage wire and a heater ground wire. So maybe the > oxy ground wire back to computer has a high resistance. Oops I made a mistake in the beginning of my message it should be computer is squirting less fuel. So fuel trims are running lean which gives you a rich code, since computer tries to correct for a rich condition by squirting less fuel. > My 96 Chevy has check engine light burning. AutoZone code reader said > rich on bank 2, which the AZ guy said generally meant Oxy sensor. I [quoted text clipped - 8 lines] > Thanks, > Libby Libby, An oxygen sensor is a wafer of ceramic (zirconium oxide) with platinum electrode foils on both sides. Zirconium oxide is an impermeable ceramic membrane that actually conducts oxygen ions through the material. Oxygen ions passing through the membrane generate what is called a Nernst potential that theoretically maxes out at about 1.2 volts. The voltage is driven the the concentration of oxygen on the both sides of the membrane. Therefore by reading the voltage you can determine the cocentration of oxygen in the exhaust. If your ceramic membrane fractures your sensor is toast. If your ceramic membrane cracks the degree of damage will vary with heat, should get worse as it heats up. Also, the platinum electrodes can peel off the ceramic, or the platinum can become contaminated with excessive sulfur or other contaminants, but it does not take much functioning platinum electrode to generate a decent voltage. Almost all the modes of failure are temperature dependent which means that while it is intermittent failure you should be able to identify a pattern. None of the materials in the sensor itself will self heal with temperature, however, there are also internal connections that just might. Good luck > My 96 Chevy has check engine light burning. AutoZone code reader said > rich on bank 2, which the AZ guy said generally meant Oxy sensor. I [quoted text clipped - 6 lines] > failing? I have checked for vacumn leaks and found none. > The code is P0175 Thanks, Libby Bank-2 injectors are producing a longer pulse width than bank-1 because the injectors are stubborn or one injectors aren't working properly that the other has to compensate. Let's say, a normal idle is at 15ms. Unplug an injector connector on bank-2 would result with 30-40ms on both injectors on Bank-2. First you have to be certain the O2 sensors are performing equally to bank 1 which you say it does. (My original O2 sensors last over 250K.) Additional info: The truck has 150,000 miles on the motor / oxy sensors. The check engine light is going out when the weather is cooler, and coming back on when it warms up outside. I would think that the MAF sensor would be more sensitive to temperature than the oxy sensor (which is a heated 4 wire version). The engine smells strongly of gas, which makes me wonder if it might be possible that the MAF sensor is registering wrong, making computer think we need more gas on bank 2, which the oxy sensor is then correctly noting as the gas pours thru the exhaust. But if that was the case, it would be rich on both banks, right? Thanks, Libby > > My 96 Chevy has check engine light burning. AutoZone code reader said > > rich on bank 2, which the AZ guy said generally meant Oxy sensor. I [quoted text clipped - 14 lines] > O2 sensors are performing equally to bank 1 which you say it does. > (My original O2 sensors last over 250K.) > Additional info: The truck has 150,000 miles on the motor / oxy > sensors. The check engine light is going out when the weather is [quoted text clipped - 6 lines] > correctly noting as the gas pours thru the exhaust. But if that was > the case, it would be rich on both banks, right? Correct.. if it was a MAF sensor problem you'd see it on both banks.. keep in mind however, that more common failure mode would be a lean condition. As I stated earlier the best way (possibly the only way) to troubleshoot this would be to look at real time data stream.. things of interest to me would be what each O2 sensor is doing (I'm assuming that we've been talking about bank 2 sensor 1), fuel trim, various temperatures (though most of them would affect both banks), pulse width, and anything that seemed out of normal. possible problems could include bad O2 sensor, exhaust leak, problem injector, misfire.. Jim > Additional info: The truck has 150,000 miles on the motor / oxy > sensors. The check engine light is going out when the weather is [quoted text clipped - 28 lines] > > O2 sensors are performing equally to bank 1 which you say it does. > > (My original O2 sensors last over 250K.) Well if you smell alot of gas when the engine is hot, then maybe you are really running rich. So my earlier hypothesis of a rich biased oxygen sensor is wrong because that would actually make bank2 run lean because computer is listening to bad input from oxy sensor 2. So if engine is somehow running rich and oxygen sensor also reports rich and computer trying to compensate by squirting less fuel and still rich, then somehow fuel pressure might be too high to only that rail? Or only on that rail is injectors are dripping fuel. I once saw a Bronco 2 where the wire to common injectors on a bank was melted to exhaust manifold causing half the injectors to pour out gas, but it eventually fouled those plugs and engine ran terribly and spark plugs fouled black. What you could do is look at sparkplugs on bank 2 and see if they are fouled dry black which usually means running rich, however if they are really white, white usually means they are lean. Also have someone see if engine is missing. But if engine missing and raw gas goes unburned then usually oxygen sensor will think unburned oxygen is a lean sign so computer compensates by squirting lots of gas but should then set lean code, not rich code. So if bank 2 is really running rich and code is for rich then only too high fuel pressure only on bank 2. Unless you have a gm vehicle with a fuel pressure regulator inside the intake which could leak only on one bank, these also have lines to regulator which could theoretically leak only on one side. but most of these don't have seperate bank 1or 2 control. Or you could have bad injectors only on that side, or somekind of short on that bank, through wiring or in computer. I would be interested in your final solution, please post it. > My 96 Chevy has check engine light burning. AutoZone code reader said > rich on bank 2, which the AZ guy said generally meant Oxy sensor. I [quoted text clipped - 5 lines] > 2. So now I am wondering if the oxy sensor could periodically be > failing? I have checked for vacumn leaks and found none. Couldn't you swap the left and right O2 sensors to see if the error code changes to the other side (O2 sensor bad) or stays the same (something else is bad)? I think that is a good idea; however, to get o2 sensor off on right side you have to disconnect exhaust from header and I was too lazy to do that. I guess I am going to do it now anyway as that will tell the tale on the o2 sensor for sure. shouldn't it be larrycurlymoe rather than larrymoecurly? :-| > > My 96 Chevy has check engine light burning. AutoZone code reader said > > rich on bank 2, which the AZ guy said generally meant Oxy sensor. I [quoted text clipped - 9 lines] > code changes to the other side (O2 sensor bad) or stays the same > (something else is bad)? |
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