1991 Camry 2VZ-FE Engine; CO Emission Failure

The test results point towards an air/fuel mixture that is too rich - too much fuel for the amount of air.

The 2 most likely causes of a rich mixture are a poorly functioning O2 sensor or O2 sensor circuit and clogged fuel injectors are dribbling fuel into the combustion chamber so the fuel does not burn cleanly or there is too much fuel.

fuel injector service may improve the emissions results if the O2 sensor circuit is checked out.

Look, its a 91, even though its low milage. Get some specifics on what a "fuel induction service" really entails.

Air cleaner element should have been done recently. Timing should be adjusted to factory spec. More likely is that the catalytic converter has given up or is marginal. Also replace the O2 sensor(s) if you don't know when or if these have ever been done. A reputable shop will be able to identify whether the O2 sensor(s) need replacing without puttinh new ones in to see what changes. Don't feel you have to use genuine Toyota parts: compatible replacements are perfectly suitable. If the cat is replaced, you will need to drive it for a while to get it working properly.

The good news is that the HC is low, which means that the valve stem seals and rings are OK.

Stewart DIBBS

How is the driveability of your Camry, Vince? Hesitation, rough idle, poor mileage, stalling?

Ray:

I declined the fuel injector service. The service advisor was reluctant to test the O2 sensor circuit. The technician finally did test the O2 sensor/circuit; the documentated results are as follows:

"Found O2 sensor not fluctuating as designed. O2 sensor stays at 0.68 volts. Resistance above specs, 12 ohms. "

I would like to know what the "resistance specs" are for this O2 sensor ? Am I correct to understand that the resistance should be much lower than 12 ohm and that the higher > 0.45 volts indicates rich fuel mixture ?

Maybe I guessed correctly, and the dealership guessed incorrectly .

Please, would you expand on what you mean by "O2 circuit" ? Other than the sensor itself, I think that you mean the wiring between sensor and the ECU input port.

~ Vince ~

None of the above.

I only estimate the gas mileage/consumption by eyeing the amount of gas in tank at time just before filling up tank and noting the trip odometer reading. Still getting about 18 to 19 mpg around town driving.

Wednesday the car was on the dynamotor for the NYState emissions testing; mechanic volunteered to comment that there was no indication of mis fires, and in his words "ran beutifully".

Vehicle went into shop at 60,492 miles and failed NYS emissions (CO) testing.The engine tuneup at that time ( last year ) included plugs, air filter, and PCV valve. Supposedly, timing was done at that same time. I am the primary driver and I feel that there are no driveability problems, even at this time.

~ Vince ~

I can only quote, if interested, what is written in the dealerships schedule maintenance booklet in the "Optional" section. It does not mention emission gases, but rather does mention driveability/performance.

I am somewhat converned that this booklet is designed for the more recent model years, and not a 1991.

Two years ago, at 58,129 miles driven, the vehicle failed emissions testing at a different Toyota dealership (the one that I was using for the first 12 years of life on this car). They diagnosed EGR valve and CAT, both were replaced, but still failed NYState emissions. I was issued a Waiver. I complained to DMV; they slapped hand of that dealership. My complaint to credit card company resulted in their investigation, and the credit for approximately $1200 was granted, permanently. I did not dispute the engine oil/filter replacement job and paid the amount required.

So, the EGR valve (first) and then the CAT had been replaced in MAY

2004. Is there any resale value for a CAT or EGR valve ? I kept the parts that shops replace, including the plugs and air filter that were replaced in year 2005/MAY.

Can anybody advise me of what the book labor hours for replacement of an O2 sensor that is located in the rear bank of this 2VZ-FE engine ??? Is two hours of labor reasonable for this job ?

~ Vince ~

The 02 sensor votages will fluctuate between .2v to .8v about 8 times every ten seconds on a proper engine. The voltage reading is directly proportional to mixture content. High steady numbers are rich, low steady numbers are lean. For example, a malfunctioning 02 sensor unable to generate high voltage would trick the computer into thinking it is running lean, increasing the mixture. But most of the time the computer would light the MIL indicating that there is no feedback response from the sensor after increased fuel trim. The reason I asked about driveability was my suspicion of the engine coolant temp sensor. I've seen on more than one occasion the ECT (towards the end of its life) report lower than actual coolant temps. This causes the computer to go into "open loop" mode, ignoring every other feedback until the operating temperature is reached, done so by richening the mixture. But, when the engine is really already up to temperature that rich mixture increases CO content and since some fuel doesn't get burned at all the HC content increases as well. A thermostat stuck open will also prevent the engine from reaching operating temp and cause a similar situation. And as a result the car doesn't quite run like it should because of all that extra fuel. Just a thought. But anyway, if this car were in my bay I would verify that the ECT is giving proper feedback, the engine is up to temp, and the 02 sensor is doing what it should. Without knowing if the engine is in proper running order cleaning the fuel injectors sounds like a shot in the dark.

Please define/spell out fully for me:

MIL ECT

Thanks.

An MIL is a Malfunction Indicator Light, which the proper term for what is commonly referred to as a check engine light.

And ECT is an Electronically Controlled Transmission. I'm pretty sure qslm meant "ECU," or Electronic Control Unit.

When you are evaluating advice and information, it is helpful to know the background of the people providing the advice and information so you can evaluate the validity of that advice. Some of the people providing advice here are very knowledgeable car enthusiasts; others are shadetree mechanics whose knowledge varies widely. In my book, a mechanic is someone with the basic knowledge of how the mechanical parts of a car work, and a technician is someone with more detailed knowledge of the entire car, including the electronic systems.

Qslm is a Toyota Certified Master Diagnostic Technician, which is the highest certification a factory trained technican can earn. And MDT has to have a Master Technician Certification from the National Institute of Automotive Service Excellence (ASE), have a minimum of 5 years experience working at a franchised Toyota dealership, and have taken and passed every technical course Toyota offers to technicians. Qslm's advice is excellent and I highly recommend following it, even if it differs from mine.

I am a former Toyota employee, among the various positions I held was District Service Manager (DSM). I used to hold a Toyota Master Technican certification (the predecessor to MDT) and ASE Master Tech certification, one of the few DSM's to hold those certifications. I called on Toyota dealership service departments and often helped them fix problems that they were having trouble with. I have never worked as a line technician so I do not have the everyday experience that qslm has, but I am a very good test-taker and fair at theory, which enabled me to pass the tests to get those certifications. It has been 13 years since I worked for Toyota so I'm a little rusty and missed the possibility of the coolant temperature sensor that qslm suggests below. qslm sees this stuff every day so he is a lot sharper than I am, although I'll continue to give it my best shot.

The resistance should be between 5 and 6 ohms, and voltage is supposed to vary between .2 and .8 volts at least 6 times in 8 seconds.

The purpose of the O2 sensor is to provide feedback to the ECU by measuring the amount of oxygen in the exhaust has. The lower the oxygen content in the exhaust, the higher the voltage output from the O2 sensor. Since your O2 sensor's signal is steady instead of varying, the ECU figured something is wrong and turned on the check engine light. When the engine is warmed up, the O2 sensor takes a reading, sends a signal to the ECU to adjust how long the injectors are open, and then takes another reading to see how the change in injector duration worked, and keeps making adjustments.

A common mistake when working with error codes from computers is to assume that if the code points to the O2 sensor, then the O2 sensor is bad. This is often but not always the case. You are correct in that the "circuit" refers to the wiring between the sensor and the ECU input port. For example, a connection may have come loose or a wire damaged. That is why I tell people to check this circuit or component and not just replace the component.

qslm can confirm this, but the lack of drivability problems and the results of the checks on the O2 sensor point to a bad O2 sensor.

Automotive systems have not changed that much since the advent of electronic fuel injection. Since 1996, all vehicles sold in the U.S. have On Board Diagnostics generation II (OBD II), which provides standardized outputs and trouble codes across brands, but the theory behind engine and emissions control has not changed a whole lot.

Assuming that a new O2 sensor solves the check engine light problem, you can try using fuel injector cleaner yourself. I recommend the stuff that Toyota dealers sell in the parts department or Chevron Techron fuel injector cleaner. Both of these products are added to the fuel tank. Be sure to follow the directions exactly, especially the amount of fuel in the tank when you add the cleaner and how quickly you have to use the fuel up.

Book labor hours, known as Flat Rate Time varies depending on which book the service department is using. Most dealerships use Motors or Chilton books and flat rate times for that job is probably 1.5 to 2 hours, including diagnosis, testing, and replacement.

Thanks Ray, I appreciate the endorsement.

In this case, I was abbreviating the cooltant temp sensor as the ECT (engine coolant temp), and as I was typing it didn't even cross my mind that the much more common and accepted accronym for ECT is the trans.

Yeah, Ray is spot on. I was just reading the original post and I missed that line where the 02 sensor was pegged @ .65v. That doesn't fly, and before anything else is done (like a fuel injector cleaning service) you need to see that sensor fluctuating from .2v to .8v about 8 times every ten seconds.

RAY: Again, I thank you. Your information is very much appreciated.

My background is electronics engineering technical writer, with a degree in electrical engineering (1979). Hence, my question about abbreviated words/acronyms. Writing MIL-STD (Military Standard) technical manuals on radar and sonar over many passed years has gotten me into the habit of wanting to know, up front, what the full spelling is for an acronym/abbreviation.

~ Vince ~

SNIPPED ith respect.

I assume that the importance of the amount of fuel in the tank when the cleanser is added and how quickly you have to use the fuel up is based on DIY maintenance efforts? With the dealership induction service procedure, apparently those criteria are not as important.

SNIPPED, with respect.

I was verbally quoted by Service Advisor: $173 parts, $178 labor. This shop's labor rate is $89/hour. However, the issued Invoice does not indicate dollar amounts. I might make a trip to the local library and make use of their database resources, because I do not presently have a subscription to internet resource databases. I would like to read the instructions for the O2 replacement procedure and review the Flat Rate Time numbers. In addition, I then might be able to find the trouble codes specifically for a faulty O2 sensor or for an improper feedback signal. Previous research noted that: Code 71= EGR System Code 21 = Oxygen Sensor Code 27 = Sub Oxygen Sensor Signal Code 28 = No.2 Oxygen Sensor Signal However, I am not certain that those should be associated with the

2VZ-FE engine, since I was told by the service technician that there is only one O2 sensor and that it is located in rear bank exhaust manifold. Perhaps Codes 27 and 28 are for a California engine.

I spent more than six hours yesterday waiting for repair action to be completed, and left with a CHECK ENGINE/MIL light lighted that was not lighted when I initially drove into the shop. IOW (In Other Words), the original O2 sensor did not cause the CHECK ENGINE light to be lighted. I became aware of this lighted indicator when about to leave the parking lot. No mention of this lighted light until I returned to the Service Advisor and asked "Why" ? His response was unacceptable. So, I received an explanation from the supervisor out in the shop area. He explained to me that the CHECK ENGINE light is lighted because the ECU's memory needs to be reset, manually.

Needing to reset the ECU's memory makes sense to me, but why this action was not already accomplished is yet another issue. Since the ECU's memory cannot be reset now, I feel that my concern about the possible, although non-probable, permanent damage to the ECU ( caused by attempting to use a faulty (shorted) O2 sensor as the first replacement unit) is justifiable. Because of past experience, before leaving the dealership again, I insisted that the Invoice be revised and that I be given an Invoice printout. I wanted the shop Supervisor to document that the CHECK ENGINE light was not lighted on arrival to the shop, but first became lighted after the faulty O2 sensor had been installed. I am hopeful that there is signal conditioning and a protection network immediately following the ECU's input connector port and ahead of sensitive (A/D converter) circuit components.

FYI, the following is what the shop Supervisor entered under the Invoice Recommendations:

"CAR IS GOING OUT WITH CHECK ENGINE LIGHT ON BECAUSE OF O2 SENSOR SENSOR IS ON ORDER & WILL BE IN STOCK ON MON 6-5 OR TUE 6-6 SENSOR WILL BE INSTALLED & LIGHT RESET LIGHT WAS NOT ON WHEN CAR CAME INTO SHOP REPLACEMENT SENSON PUT LIGHT ON SENSOR INSTALLED BY XXXXX TOYOTA"

XXXXX indicates name of dealership. Unfortunately, the shop Supervisor did not include ending punctuation. I appologize for the lengthy posting.

~ Vince ~

I find myself arguing the fine points with Ray far too often, but this time I'm onboard 100%.

What I would do is replace the sensor. It's a $25 part (or there abouts), and SHOULD solve the problem.

In the unlikely event it doesn't fix the problem, then you need to do more advanced diagnostic tests. If you have the capability to do these tests -- or know where all of the respective connectors are -- then it makes sense to do the tests and confirm the viability of the connectors first -- as Ray suggests. I do not have that capability, and my feeling is that odds are very good the sensor is toast. I would play the odds and relace the sensor, then do the diagnostics if that didn't work. Ray is much closer to this kind of stuff than I am, and he can do the diagnostics before blindly replacing parts. His approach is better, but mine is easier although it potentially exposes me to parts costs that I might not otherwise incur. I'd do it Ray's way if I had the means of doing so.

I give credit where credit is due!

I hear ya. The military and auto industry are guilty of using a lot of acronyms without first providing the basis for the acronym.

Since you have an electronics background, you will understand that the O2 sensor varies resistance based on O2 content in the exhaust, which in turn varies the voltage passing through the sensor to the computer.