My 1999 pontiac sunfire 2.2 liters did not pass the e-test. I feel that something tells my computer to run rich at 2000 rpm. I changed the spark plugs and the air filter. After driving 200 Klm. the engin light went on and read code po137. Low volts, 02 sesor. a rich runnig engin will make that code go on. Did someone have that problem? And what solution did you find?

I say again, Diagnostic Test Code (DTC) is "Oxygen Sensor 2 Low Volts" The reason you would replace the downstream sensor is because oxygen sensor 2 IS the downstream sensor. Just so you understand...I said to check for the upstream sensor to be reading rich or lean because if it is reading lean then your downstream sensor may not have a problem. It may be a fuel delivery or vacuum leak or leaking exhaust problem. However, if the upstream sensor is reading correctly, this eliminates fuel delivery and vacuum leak causes for the downstream sensor to have low voltage. You need to understand the MOST O2 sensor codes are NOT caused by a defective O2 sensor. The other engine data should always be examined before replacing ANY oxygen sensor. I say again, Diagnostic Test Code (DTC) is "Oxygen Sensor 2 Low Volts" The reason you would replace the downstream sensor is because oxygen sensor 2 IS the downstream sensor. Just so you understand...I said to check for the upstream sensor to be reading rich or lean because if it is reading lean then your downstream sensor may not have a problem. It may be a fuel delivery or vacuum leak or leaking exhaust problem. However, if the upstream sensor is reading correctly, this eliminates fuel delivery and vacuum leak causes for the downstream sensor to have low voltage. You need to understand the MOST O2 sensor codes are NOT caused by a defective O2 sensor. The other engine data should always be examined before replacing ANY oxygen sensor.