Your smooth and powerful Cadillac's ride is now full of hesitation, rough idle episodes and misfires - could the Cadillac oxygen sensors be at fault? Because the symptoms of an ailing oxygen sensor - failure to start, bucking, hesitation, poor gas mileage - are seen when any of the fuel or ignition components fail, you might have to use some detective work. The oxygen sensors are electrical devices, which send current to the Engine Control Unit. Accordingly, diagnosing an ailing oxygen sensor means testing the voltage and current. The easiest step is to use your electrical diagnostic kit to read whether the codes will pinpoint the problem. Under normal conditions, the voltage in the oxygen sensors will range between 0V and 1V, depending on the rich or lean qualities of the fuel. To see if the sensor can detect a rich fuel mixture, disconnect the sensor wires from the ECU, and run the engine. Remove the vacuum line and plug the area that leads to the fuel pressure regulator. The sensor should read 0.9V, which is a rich mixture. To see if the sensor can detect a lean mixture, create a small vacuum leak. The voltmeter should read 0.2V or less. To create the necessary closed loop condition for the test, you need to run the engine above 2000 rpm for two minutes.