2005 Nissan Quest Malfunction Indicator Light (MIL) is ON

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1 Check scan data for fuel trims to see if the system is in proper fuel control – look for 0% plus or minus 10% in generic or 90 – 110 % alpha in manufacture specific. 2. Verify there are no exhaust leaks. 3. Drive the vehicle and check the bank 1 rear O2 sensor activity on the scan tool or with a voltmeter to see if the bank 1 rear O2 sensor is cross counting like a typical front O2 sensor would. Potential Causes: Catalytic Converter Tech Tips: If in manufacture specific with the scan tool, Nissan displays fuel trims in alpha. 100% alpha is the same as 0% fuel trim. This vehicle has front air fuel ratio sensors – not O2 sensors. Bank 1 is the firewall bank. Bank 2 is the radiator bank. Before the catalytic converter lights off, the rear O2 sensor voltage is usually down around 0.2 – 0.4 volts or so but when the catalytic converter lights off, it uses up a lot of the oxygen so the rear O2 sensor voltage will typically reads around 0.6 – 0.7 volts and have some movement but not a lot of movement and should not cross count above and below 0.5 volts. The catalytic converter is covered under the 8 year 80,000 mile federal emissions warranty.