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1998 Toyota Camry, 2.2L 4cyl automatic, failed high CO. Does it need an Oxygen Sensor?

I really don't know much about cars so that's why I'm here to ask the specialists. :] I decided to do a last minute (as in the last day I could do it) smog check for me to be able to renew my registration. I really don't have any problems with the car- in my opinion (and others as well) my car still runs real smooth. This, and the fact that my check engine light was not on, made me pretty confident that my car would pass.. but it didn't. As I've stated, I don't know much about cars. But I'm looking at the Smog Check Vehicle Inspection Report (VIR) and I want to list out the things that the inspector highlighted.. CO (%) MAX AVE MEAS 0.50 0.02 0.96 0.48 0.03 1.28 In that part of the report, the inspector highlighted the CO(%), the numbers under MEAS, and wrote on the bottom "Failed- high CO2". The only minor detail that I could mention really is that I change the car's oil within the same week I got it checked. My dad keeps telling me to also replace the air filter and a mechanic friend of ours is telling me to replace the downstream O2 sensor. But I don't want to spend extra money on things that I don't need just to pass the smog check. Please help! Classes start in 2 weeks. :[
Answer:

The diagnosis for your 1998 Toyota Camry's high CO fault needs to begin with an inspection of the fuel injection "feedback" system. This includes ensuring the oxygen sensor is working properly, your Toyota Camry's emissions computer is receiving the signals from the oxygen sensor, the computer is computing the data properly and sending the correct signals to the fuel injectors to either increase or decrease fuel delivery to the combustion chambers. Toyota Camry Fuel Feedback Test: The feed back test will utilize a 5-gas analyzer (usually a smog machine) and propane. The smog mechanic needs to add propane to your Toyota's intake manifold and ensure the oxygen sensor is reading the added propane as an increase in CO; and ordering the ECU (computer) to decrease fuel delivery at the instant propane is added to the system. This test should be done after your Toyota Camry has sufficiently warmed up and while it's running at idle. Using a voltmeter the smog technician should observe the voltage output of your Toyota's oxygen sensor as the propane is added. Voltage should increase. If there is no increase this indicates that the O2 sensor in your 1998 Toyota Camry is defective. The sensor should be replaced and the test started over. If voltage increase is present at the sensor output the technician needs to ensure voltage increase is also present at the computer input terminal. If voltage is present at the terminal as well next the technician must ensure the computer output terminal to the fuel injectors are lowering "injector pulse rates". At the end of the feedback test it will be know whether your Toyota Camry's high CO fault is electronic or mechanical, and the technician can further diagnose the fault. As far as your Camry's air filter... I'd recommend a replacement if CO was slightly high, but in this case with the CO numbers as high as they are, I'd recommend a feedback diagnosis first. I think the problem might be more serious then a dirty air filter. posted by SmogTips Support

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