Also check for continuity to ground on the ground circuit. Then check for 12V supply to the o2 sensor’s heater circuit. If none of this is the case and the o2 sensor just isn’t switching or acts sluggish, unplug the sensor and make sure there is 5 Volt reference voltage to the sensor. If the exhaust does have holes in it, it’s possible that the o2 sensor may be misreading the exhaust because of the extra oxygen entering the pipe via those holes 3. Refer to the appropriate articles for diagnosing an unmetered vacuum leak). If the sensor operates properly, then the sensor may be okay and the problem may be holes in the exhaust or an unmetered vacuum leak in the engine (NOTE: Unmetered vacuum leaks at the engine are almost always accompanied by lean codes. The o2 sensor reading should go lean, reacting to the enleaned exhaust. Then induce a lean condition by removing a vacuum supply line from the intake manifold. The o2 sensor reading should go rich, reacting to the extra fuel added. Do this by removing the fuel pressure regulator vacuum supply briefly. If it doesn’t switch properly, try to determine if the sensor is accurately reading the exhaust or not. If it drops out, fix the appropriate part of the wiring harness where problem resides. Then perform a wiggle test by manipulating the connector and wiring while watching the o2 sensor voltage. If it does, the problem is likely intermittent and you should examine the wiring for any visible damage. It should switch rapidly between rich and lean, evenly. Solutions Using a scan tool, determine if the Bank 1, sensor 1 is switching properly.