Have a 97 Jetta 2 liter, 77K miles. The OBD code 140 (O2 circuit sensor2 bank1 no activity) has been kicking in and then going away from time to time for a couple of years. Now it seems to be on steady and is accompanied by 134 (sensor1 bank1 no activity) and 135 (sensor heater circuit heater sensor1 bank1 malfunction). Am I due for a new O2 sensor (it has never been replaced)? Car runs fine.
You have a problem with the wiring, not the oxygen sensor itself. Check the wiring harness. You may find it melted to the exhaust, or some other obvious fault.