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1997 Toyota Camry Engine Malfunction Light

I have been maintaining and driving this car for the last 12 years. Back in February this year, the Engine Malfunction light started showing up for days and then would go away. This happened many times over. In February, the local Toyota Dealer said it needed an Air/Fuel Ration sensor and an Oxygen sensor (OPCode - 51); est. cost $796.00+. I interchanged the air/fuel ratio sensor (on the exhaust manifold near the radiator) with another from my 2004 Camry without any result. I am not sure exactly where the oxygen sensor is. I would like to try replacing that sensor too and see if that eliminates this problem. As far as the car’s performance is concerned, it has not deteriorated - it still gives me 28-30 mpg as before (it’s a 5-spd manual). Also cost of parts from an autopart store is only $280.00 and not $446.00! as Toyota told me. And the time to replace these parts should not take more than half an hour. So, I don’t know how a Toyota Dealer can justify charging $796+ for this repair. Anyhow, do you have any suggestion for me? I will really appreciate any helpful advice I can get from you.

Thank you.


This car should have OBDII Diagnostic Trouble Codes which read like P0123. While the Check Engine Light is on or soon after, have the codes read by a compatible code reader. Post the codes back and we can go from there. Does this car have the 4 four cylinder engine or the V6? How many miles on the odo?

Many autopart stores will read those codes for free. Remember it is the code we needs (Like P1234) not someone’s interpretation of what that code means.

You are presenting codes in the wrong format and your car does not have a Engine Malfunction Light or a Air/Fuel Ration sensor. I submit you are over your head.

Everyone if they really want can become more knowledgeable. Compared to the spelling errors we see here changing air/fuel ratio sensor to air/fuel ration sensor is a trivial error, not deserving of insults. Note that the second time he used the term he spelled it correctly. So, it was most likely a typo.

I bet 90% of mechanics would understand what he meant by Engine Malfunction light. Come to think of it, so did you, right?

People come here to learn, not to be slapped down.

OP, dealers have to charge more than you need pay if you provide your own labor. If you have the tools, and know how to replace these parts, it is a darned good idea to do so. Be aware that some cars, some models, are really fussy about replacement parts, which is why the Toyota dealer looks up the parts by VIN (car number visible through the windshield on most cars these days.)

A lot of people use non-dealer mechanics, and this is a lot cheaper. The dealer may have to pay Toyota more for genuine Toyota parts than you would pay at a parts place. So, if you want it done by Toyota trained mechanics with their parts, you will need to pay their price.

Somewhere on this URL is a page called something like Mechanic Files, and there will be recommendations of good mechanics reported by satisfied customers. Find one who can get parts for your car, and it will usually be cheaper.

In McAllen, where I live when I am in the States, there are some good mechanics, a few. There is a cultural problem there, so there aren’t many. Those mechanics are so in demand that they sometimes require the car to be left for several days until they get down to it. I take mine to the dealer, and so far with few repairs on my 2002 Sienna have received good service – except the very first oil change, which was also my last. (They promised in advertising that they used genuine Toyota parts, and I am sure Pennzoil is not genuine Toyota parts. Since there are oil disposal places now, I change my own.)

Is there a device called “air fuel ratio sensor”?(titanium type 02 sensor) which does generate different voltages dependant on air/fuel mixture but are still oxygen sensors. It was important to tell the OP about the improper use of Engine Malfunction Light because the “Check engine” does not indicate a mechanical malfunction of the engine as many people think it does. They don’t know that the “check Engine” light primairly indicates a failure in the emissions control systems of the automobile. It is important to use the correct terminology and know what systems are related to what warning lights. No slapping down inflicted just education. And he needs to know the proper format to present OBD2 Codes and be able to find the 02 sensors and know what type his car uses (wide or narrow band). If he could find a 'air fuel ratio sensor" in the exhaust manifold but not regognize a 02 sensor he may as I submitted be in over his head.

That A/F ratio sensor for a Cali car can be purchased her,carcode,1273610,parttype,10328

It appears to be a wideband oxygen sensor.

Dear Researcher, Thank you very much for your response to my question. I will try to have OPCODE re-read and interpreted according to the OBDII format as you suggested. As for my car, it’s a 4-cylinder engine with 112,000 miles on the odometer.

Dear Oldschool, Thank you for your response. I am sorry about the typo errors in my question. This is really the OPCODE (51) I received from the Toyota Dealer with the following explanation: “Advise - needs air/fuel ratio sensor & oxygen sensor.”

In the User’s manual Check Engine Light is termed as Engine Malfunction Light.

These sensors make perfect sense to me to warn against improper combustion.

So it is “Toyotaease” we are dealing with

I couldn’t help you with a OPCODE (51) but I could help you with a OBD2 code

The air/fuel ratio sensor is a oxygen sensor just a more advanced/different type

I do believe the term Engine Malfunction Light does lead people to a false conclusion as to what is being monitored by the OBD2 system. It won’t tell you why the car won’t start and this certainly is a engine malfunction.Certain aspects of OBD2 are generic and required but the manufacture is free to add extra capabilites to their paticular version.

The wide band and narrow band 02 sensors are much more than combustion monitors they are the leaders of the band,as they have feedback (they present information to the PCM which controls how the car runs).

Thank you for your response. I am going to have this Engine Check Light (Engine Malfunction Light) read by another Toyota Dealer’s Repair shop and see if I can get the OPCODE in the familiar format (e.g., P0123) as suggested by Researcher. The Engine Check Light is a catch-all warning light for a number of problems not necessarily related to the engine operation alone. It could be even for the gas tank cap as VMV noted in their vehicle registration renewal notice a couple of months ago.

As for the two sensors, they pretty much look alike - perhaps both are oxygen sensors but with different price tags!

Check the VECI label under the hood. If it says that your 1997 Toyota Camry car meets California emissions standards, then, you must use a wide-band A/F (even, if you don’t live in California) oxygen sensor in the front of the catalytic. If it says Federal, then the front oxygen sensor is a regular type.
The oxygen sensor on the rear of the catalytic converter is a regular type, regardless.
The signals from the front sensor and the rear sensor are compared to each other to indicate the health of the catalytic converter. The caveat is that both sensors, must, themselves, be healthy; other-wise, they will be inaccurate.
A front A/F wide-band oxygen sensor is $150+.
A rear oxygen sensor is $100+.
Be sure that you get sensors that you don’t have to cut the wires and attach terminals. For a few dollars more, it’s better to get the sensor with a plug on the end attached. Further, be careful that the sensor wires are the same length as your old one. One with leads too long can cause routing problems.
The code you got (OP Code 50) is causing confusion, here. If you don’t live in California, you can get the OBD II codes read at many auto parts stores. Those, in their raw form (P0420, etc.), would help us much in postulating a diagnosis.

Very helpful advice! Thank you so very much.

The Feds consider the gas tank cap related to the engine (this could be a good debate). Like I stated OBD2 or the representive you see “Engine Malfunction” is related to emissions and keeping the car from polluting (whether out the tailpipe or evaporative emissions). Toyota is free to add extra capabilites to their on-board diagnostics as long as the meet the min. set by the Feds.

With ODB3 (which is delayed for some reason) our cars a going to be equipped with tattle-tale devices that notifies “big brother” when our cars are not running right. I can hardly wait.

I had the Engine Check Light (Malfunction Light) re-read by another diagnostic tool at an autoparts store and the following troubleshooting codes and probable causes were suggested:

P0171 - Air/Fuel mixture system lean bank 1

Probable causes:

  1. Low fuel pressure
  2. Faulty MAF/VAF sensor
  3. Cylinder misfire condition
  4. Faulty hO2S/AF sensor
  5. Large vacuum leak

Remark: As the engine has been running well with no loss in mpg, I tend to think
causes 1 and 3 would not apply but about 5 I am not sure; have to check.
Have any ideas?

P1133 - Air/Fuel sensor circuit response. (bank 1 sensor 1)

Probable causes:

  1. Open or short circuit condition
  2. Poor electrical connection

Remark: Both are highly unlikely, but I am not sure. Do you have any suggestions?

Thanks for the codes. Now you have some diagnosis to do. The codes are telling you that the A/F sensor is reading a constant lean condition. A lean condition to the ECM is a constant low voltage or a voltage that cannot be brought high. So you have to find out it there truely is unbound oxygen in the exhaust; the voltage from the A/F sensor is not getting to the computer; or the computer is unable to interpret the voltage correctly.

You have tried two probably good A/F sensors without a change. So the A/F sensor is probably not suspect.

I would have the fuel pressure checked just to rule out a failing pump, faulty fuel pressure regulator, or clogged fuel filter.

I believe that this engine still uses the Manifold Absolute Pressure sensor to determine one engine load parameter. Since you don’t have a driveability problem, its failure could probably be ruled out.

A cylinder misfire would probably be setting other codes or at least be recorded in the misfire count. So, you probably don’t have that problem.

A large vacuum leak would cause driveability problems – most likely a high idle, stumble, hesitation, and poor fuel economy.

One item not covered in the P0171 code ‘probably causes’ is a leaking exhaust system ahead of the A/F sensor. If air is somehow getting into the exhaust ahead of the A/F sensor all attempts by the ECM to richen the mixture is not going to correct that. The ECM can be commanding full rich but that extra oxygen in the exhaust will still be there until the gases hit the catalytic converter.

Further diagnosis is going to be aimed at seeing if the A/F sensor can be brought from low voltage to high voltage by externally richening the mixture. The sensor reading can be observed by doing a real time data scan using a capable scanner. The mixture can be richened by releasing propane into the intake. Another test is to actually analyze the exhaust gasses ahead of the cat and attempt to force the mixture.

Well that should be enough for now. Let us in on the progress especially if you find out the solution.

I am very thankful to each one of you for your helpful suggestions to resolve this problem. Yesterday I had my car checked out by a recommended local mechanic and had it fixed by him for $301.00 (A/F Ratio sensor $235.00 from Toyota for my car’s specific VIN and the rest for labor and taxes). The front A/F Ratio sensor was the culprit. I tried to check it earlier by changing it with a similar sensor from my 2004 Camry . But it did not work probably because it is a vehcle specific part. Another thing is that I needed to reset the error code in the car’s computer without which the engine check light would not go away. What I did not understand as to why I must have a vehicle specific sensor from Toyota which the mechanic recommended and not any other cheaper sensor from some other auto parts store. Do you have any comments on this issue? Could I use a cheaper sensor (about $140.00) from another manufacturer like Bosch and still resolve this problem? Thanks again.

Thanks for coming back with the resolution. With all the symptoms, I/we were certain there would be multiple causes; but, it turned out to be only the front wideband (A/F) oxygen sensor (California emissions standards system). You saw the value of a scan tool when properly used in capable hands. A good mechanic can make a good tool GREAT. A poor mechanic can make a great tool poor.
I’m sure that a Bosch, or Denso, A/F sensor would be just fine. Toyota may have put their name on one or the other, anyway. Part numbers for 1997 and 2004 Camry A/F sensors DON’T match ( )