How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Skyvisions Your Own Question
Skyvisions, ASE Certified Technician
Category: Toyota
Satisfied Customers: 14504
Experience:  Toyota Master Diagnostic
Type Your Toyota Question Here...
Skyvisions is online now
A new question is answered every 9 seconds

1995 toyota corolla, 1.6 failed emissions hc(ppm)269 co2%1.31,

This answer was rated:

1995 toyota corolla, 1.6 failed emissions hc(ppm)269 co2%1.31, during the test the check engine light came on, showing code 25. Proir to the test, new plugs, properly gapped, nee cap, rotor, air filter, oil change, lucas fuel additive, the fuel additive was run out before test. hayes manual says timing is adjustable. It is fixed, seems to be off a few degrees. Need help lowering emissions


You have many options with today's internet so Thank you for choosing


You probably mean CO which is short for carbon monoxide. The code 25 is for the oxygen sensor. The car is running slightly rich. On these older Corolla's I have found that the oxygen sensor when malfunctioning will affect the CO output. If you change the oxygen sensor it will probably pass the emissions test.




P.S. I take great pride in providing quality responses for the people I assist. If you believe that I have been professional and helpful in my assistance please don't forget to give a positive rating for this exchange and click the accept button. If your feel my answer does not address your issues, please just tell me and I will opt out, allowing another technician to address your situation. My Goal is to make this experience one you appreciate.

Customer: replied 8 years ago.
O2 is fine according to tests so what else might I be looking at, my timing is a bit off as well though I don't know if that makes a difference

I am confused in your initial statement you said there was a code 25. This is a malfunction of the O2 sensor. Is the O2 sensor toggling from .1 Volts to .9 volts several times in one minute?




Customer: replied 8 years ago.
according to my hanes manual a code 25 refers to injector/injector circuit, oxygen sensor/circuit, ECM, Fuel pressure regulator Coolant emp sensor/circuit, Intake air temp sensor/circuit, Vacuum or exhaust leak, contamintated fuel, and/or Ignition system, here is a link to the test I used, I also went to the junk yard and grabbed another O2 sensor and it reacted the same way as my old one

The Haynes manual is very generic and description. A code 25 is an indication of a lean condition. A lean condition will screw up the emissions output at the tailpipe. 90% of the time when you see a malfunction in the O2 sensor and you get a code 25 it will fail the emissions on CO. To properly test an oxygen sensor you need a lab scope. If you monitor the voltage swings from 0 to 1 volt you should see 8 to 10 voltage swings per minute. You can check this with a volt meter also it just is not as accurate. You can probe the OX1 pin in the diagnostic connector under the hood for easy access. More than likely you will find that the oxygen sensor is bad.






Customer: replied 8 years ago.
I went to the junk yard like I said and grabbed another O2 sensor, I decided to put that one in the car in place of the other, I used the same test as I did on the last one and they both appeared to act the same, the cahnces of getting 2 bad O2 sensors are low but not unheard of. Throughout my reading of the manual it would seem to indicate that I have a California emissons system on the car, other than the tests you are suggesting is there any way I can tell if this has done any good for the vehicle without having to go in for a 3rd emissions test and failing again. I'm a poor college student that already has 100 dollars between 2 emissions tests and don't want to go in another 45 to fail, not to mention the bit i've put in to replace the other parts.

Have you actually checked the voltage swings of the OX1 pin in the check connector? HC failures are due to partial burn of the air fuel ratio mixture. If you have already checked and replaced Rotor wires plugs and so on these things are all ruled out. Secondary ignition is the primary reason for failure on HC emissions. I understand your situation being a poor college student and all. But I have my limitations setting behind his keyboard. If the compression is low on the cylinders or if the rings are weak excessive oil burning can cause HC to be too high. The only other cheap option I can think of would be to dump some STP in the oil to try and thicken up a gap in the cylinders. Not exactly my kind of fix but it might work for what it's worth give it a try. I am not a fan of used engine parts at least not without their own testing. The only other option would be the catalytic converter. If the catalyst is not function properly it cannot convert the right chemical mixtures to eliminate the HC and the CO2 and the CO. Unfortunately converters are a last resort and very expensive let me know how things go.




Skyvisions and 3 other Toyota Specialists are ready to help you
Customer: replied 8 years ago.
sorry for the wait, just had the car tested again and it passed


On the Road again! I just can't wait to get on the road again! (John Denver I think) Good job.




If you need anything in the future ask for me. I am usually around.