1991 Camry 2VZ-FE Engine; CO Emission Failure

Actually Ray, an o2 sensor is a regular galvanic (sp?) battery that produces voltage. Part of the sensor is exposed to atmosphere, the other to exhaust. The difference in oxygen content between these two "halves" is what produces the voltage. During lean run, the oxygen content is high in the exhaust stream and the difference in content is small. During a rich trend, the o2 exhaust content is much lower than the atmosphere side of the sensor, so voltage increases. You can actually unplug an o2 sensor and measure voltage directly with the car running! The fluctuating voltage is a function of the ECU. Instead of trying to hold the fuel trim at a steady rate, the ECU runs the trim rich-lean-rich-lean. This occilation over a given period of time produces a fuel trim trend that averages out to be stoichiometric mixture. The new "air fuel ratio" sensors differ in this design, as do the circuits in the ECU. The new sensors are able to hold the fuel trim at a specific value and no longer need to vary it like before, giving to more efficient operation. This is why the two different sensors cannot substitute each other. Why I can recall this stuff at the drop of a hat but can't remember where I put my car in a mall parking lot baffles me.

The OP already knows that the O2 sensor is bad because it was already tested as bad by the dealership.

Since the OP is familiar with electronics and probably with the use of a multimeter, we can talk him through the checks if he wishes to do so himself.

Now that you mentioned it, I do recall learning this a long time ago; I stand corrected!

I've noticed that there is a new type of sensor that uses a different principle but don't really know much about it.

I have the same problem with losing my car in the parking lot at work ;-(

A ~$25.00 O2 sensor has to be cheap aftermarket. I thought brand name aftermarket O2 sensors ran in the $40 to $60 range, and OEM sensors in the $120 range.

Some aftermarket O2 sensors have "universal" connectors that require cutting and splicing wires. If you are going to cut and splice, I recommend cutting the pigtail off of the old one and grafting it on to the new sensor.

The hardest part of replacing an O2 sensor is dealing with rust and reaching the sensor if it is on the rear bank.

The O2 sensor is installed in the exhaust manifold and is either threaded and installed like a spark plug or it has a flange and is held in place with

2 10mm bolts on the flange. It will have a pigtail with a connector at the end of the pigtail.

Youzers! I've bought a few O2 sensors in my time for various cars and trucks that I've owned, or still own, and they ran me in the range of $25. I haven't had the displeasure of buying one for my Toyota yet.

Have you tried the local parts store, instead of the Stealership?

Labor entails a connector to unplug and plug in again, and a device that roughly resembles a spark plug to be removed using a tool that roughly resembles a socket wrench.

Dude, sorry to hear of the actual pain.

Talk to Ray some more about the diagnostic method, it appears that the learning curve may cost less than the experimental parts that come with my method of doing repairs. Wow.

Can somebody point me to a Glossary of automotive terminology?

My memory is not what it used to be. I now do not recall if ECT is engine control unit or electronic control unit. So, a glossary would be helpful. Furhtermore, my memory is not what it used to be.

There is a section in the Toyota Factory Service Manuals that explains acronyms used in the book. The Society of Automotive Engineers (SAE) may also have a glossary but I believe that access requires membership in the SAE. I let my membership expire when I wasn't being reimbursed.

For Toyotas:

ECT: Electronically Controlled Transmission or Engine Coolant Temperature (sensor).

ECU: Electronic Control Unit

I am not a gambler; so when the O2 sensor was not yet "tested" on FRIday, but an induction service recommended only, I spoke up, becasue I did not like the odds.

UPDATE INFO: It does appear that those advanced diagnostic tests to which you Jeff, refer, are going to be required. I say that because my ill 2VZ-FE engine equipped 1991 Camry is in the hands of the dealership again beginning today.

A second O2 sensor was installed this morning while I waited/spoke to the parts counter guy about fuel injection cleaners, etc. I was then told by the Service Advisor (SA) that there is a problem with the just installed O2 sensor. Not much further details given, but they did provide me a loaner '06 SCION (n/c), and said that their call probably will come sometime tomorrow.

QUESTION: What other advanced diagnostic testing might they need to perform at this point, Ray/Jeff/Qslm, other than the "circuit connectors" ???

As a reminder, the vehicle arrived last FRIday without any MIL lighted, the first O2 replacement sensor apparently triggered the CHECK ENGINE light, and the EMU cannot be reset.

I spoke with a different SA this morning, and discussed the timing of the NYState emissions reinspection with him. I wanted the NYState emissions reinspection done today. He first stated that the emissions inspection should not be done immediately after the O2 sensor replacement; something about calibration is needed and that is accomplished by allowing the vehicle to be driven some unknown amount of miles between O2 sensor installation and the time of the NYState emissinos reinspection. Then he took note that this is a 1991 model, and that the delayed inspection "might not be needed, we'll see".

My wife is just now returning home and she sees the SCION in our driveway. She might think that I bought a new car ! ! And, I would wager, because of her opion of the Chrysler ?? whatever its name is, (the one that looks like a miniature hearse), she is not going to like the shape/appearance of the SCION either.....

Thanks ~ Vince ~

I do not know what "advanced diagnostic tests" Jeff Strickland is referring to.

As I have mentioned several times, checking an O2 sensor does not require advanced diagnostics, unless you consider measuring voltage and resistance 'advanced.'

2 bad O2 sensors in a row is a very unlikely event. Either the ECU is bad, someone damaged the ECU, or the wiring between the O2 sensor and the ECU is bad. The rate of failure of ECU's is very low. In fact, the service facility that examines ECU's returned for repair only finds 1 or 2 bad ECU's every 2 or 3 years out of the hundreds of ECU's returned every year.

The dealership will probably have to crack open the service manual and do some basic diagnostics.

The factory service manul has a repair matrix/flow chart to follow. Diagnostics is not very "advanced" but it does have to be done thoroughly.

I have never heard of any need to delay emissions inspection after an O2 sensor replacement. The service advisor does not know what he is talking about.

SNIPPED

I was able to get some specifics today Stewart.

I also asked the parts counter guy to see the available BG fuel system cleaners. For later reference, I attempted to write down the chemical content of the products that were made available to me. Unfortunately, however, I have not ever studied chemistry ~!~

I was shown 3 products:

BG p/n 203,

a Service Kit that includes BG p/n 208 and BG's p/n 210,

and a relabelled can that is intended to be used during the "BG Induction Service". I believe this relabelled can is BG's p/n 408 (based on the description provided at

). The label did not show any chemical content on this one. I believe that I now have a working knowledge of how and why each of the three products listed above is intended to be used and pricing info for each product.

I have yet to see the label on the Chevron Techron fuel injector cleaner; however, I believe that it is equivalent to the Service Kit described above.

That is great news for me. Thanks.

Is there a wrap-around or some type of diagnostic test that the dealership repair shop can perform prior to declaring the ECU faulty ?

In the military world, a Maintenance Dependency Diagram (MDD) sounds similiar to the repair matrix/flow chart that you mention Ray. The MDD showed the signal path and matrix branches. The identity of all mating connectors, relevent voltage and resistance information, and signal waveform (o'scope) photographs are included.

When reading Jeff's previous comment, I shall mentally replace "advanded diagnostic testing" with "additional diagnostic testing". As with the MDDs, the fault isolation procedure was not difficult, but needed to be performed carefully and thoroughly.

IMO, B&G products are OK. They are not available to the general public and are only sold through service facilities.

The Chevron Techron is a DIY product.

I've heard very good things about Motor Vac, also available only through service facilities.

In any event, I doubt if a fuel injector service will fix the problem with the O2 sensor.

Yes.

The Toyota diagnostic matric sounds similar to the MDD that youa re describing, except that there are no photographs.

Jeff was advocating that you replace parts first and if that doesn't work, then do "advanced" testing..

My approach is the opposite. I recommend that you check whether a particular part is good or bad before checking it, especially when a part like an O2 sensor can be checked in about 2 minutes. If the O2 sensor is good, then move on to the next step in the troubleshooting chart.

The biggest reason that ECU's are erroneously replaced is that the technician missed the "carefully and thoroughly" part.

I do not know which service department you are taking your car to, their reputation, or whether they have MDT's. They may be very good an running into an unusual situation or they may have dropped the ball.

Yeah Vince, as far as diagnosing EFI problems o2 system circuit inspection has to be very low on the difficulty ladder. The sensor makes voltage, voltage traves down a wire to the ECU, and the ECU interprets it based on the programming. Of all the exhaust feedback sensors I have replaced, I can remember one case where the wiring was at fault, not the sensor. And if you think about it, a component that spends its days hanging out in 1000F+ exhaust streams is far more likely to fail then a few wires that were laid down as the car was constructed. And as Ray points out, only a handful of the hundreds of "faulty" ECUs sent in are actually at fault. Then I always point out that every damn obtuse diagnostic process (MMD, to you) in the FRMs ends in "replace ECU". But anyhow, I'd have my money on the sensor here being responsible for that stuck voltage. But, we'll see. Just let us know what ends up.

Remember, I am schooled in the military electronics world. I served in Uncle Sam's Canoe Club and was first trained as an electronics technician for communicatins equipment. My last career had me

The individual field replaceable module could be either self-tested or bench tested by shipboard technicians. OTOH, a magnetron was replaced after other possible causes of poor radar video returns were tested/evaluated. It is good to know that the auto repair industry also has been designed to avoid needless replacement of field replaceable modules.

Even in the days when equipment used vacuum tubes, the electronics technician would test the tube in a tube checker prior to replacing it. So, I was taught to "fault isolate" down to replaceable component, e.g., tube, PC board assembly, rather than replace a tube or PCB assy and hope for a "fix". Signal flow diagrams included waveform photos as required, and those were referenced to within the MDDs, rather than the MDD itself including a (timing) waveform, etc. Sure, in some cases there remained more than one possible field replaceable module that could possibly cause a symptom. This is where I had to consult the electrical design engineer and possibly the reliability engineer to possibly provide a "most likely" list of the candidates.

It sounds like there is little difference in the diagnosis and repair of shipboard and automotive electronic systems.

I was reviewing the displayed certificates today, as a matter of fact. None were identified as a MDT. There were only 8 certificates of completion or acknowledgement. There were more than 8 NYState inspectors on the job at this repair shop, including one certificate from NYState that identified the FRIday Service Advisor as a ualified inspector !

Anyway, the young fella that worked on my vehicle on FRIday and today had a certificate that indicated that he was a "Certified Technician". On the line that followed were: Engine, Drivetrain, Chassis, Electrical

I do not know if there is a category specifically for EFI/emissions, but this guy was also identified as a qualified NYState inspector.

I agreee with your approach Ray. I do not advocate part replacement until that part has been isolated and identified as the cause of the problem.

I have the distinct impression that this particular repair shop has approached this particular O2 sensor problem with the notion of replace a part/perform induction service PRIOR to doing any kind of diagnosis. Honestly, I had to convince FRIday's SA to direct that a diagnostic test be made on the O2 sensor; afterall, I was going to be charged $89 for diagnostic testing.... But since there was no MIL lighted and no stored fault codes in the ECU's memory, he and/or the technician jumped on idea of induction service as the first recommended course of action. That would have been $139 + of my money wasted, IMHO. And, AFAIK, that would have meant an extra commission income for the SA.

Even in days of vacuum tube electronics, tube checkers were utilized first, rather than routinely replace tubes if, for example, a receiver was reported as low sensitivity. In such a case, the suspect/candidate tubes were pulled and checked on a tube checker for possible shorts, opens, and transconductance. Do you remember that tube checkers were available at the local corner drug store and/or at Radio Shack stores ?

I can see many parallel factors that are applicable to both the auto repair industry and military electronics equipment repair methods with regard to corrective maintenance and repair procedures. The military electronics side of this is something that I am familiar with due to my personal USNavy training as a shipboard E.T. as well as being involved with technical manual composition and training course documentation during my civilian career work.

I don't remember what the initial certification classifications are; I believe that the 4 you listed are all of the areas. The tech might just need more time or a few more classes.

I do not know what the qualifications for a NY state inspector are but if they are anything like MA, RI, NH, VT, and ME, they are not too difficult. Basically, you have to be able to look at brakes and tires for wear, check headlight alignment, look for loose body parts, cracks in the windshield, and hook up a sniffer probe or OBD II scan tool.

IMO, the shop should have run some diagnostics before recommending a repair. With your training, you should be able to easily follow their diagnosis and repair processes.

But, I do not havd a lift !