On Friday I was just driving along and my check engine light came on. I read the codes with a code reader and both those codes came up.
P0134 - O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 1)
P0154 - O2 Sensor Circuit No Activity Detected (Bank 2 Sensor 1)

It seems very unusual to get both of those at the same time and even more unusual that both upstream 02 sensors would fail at the same time. Does anyone have any ideas or suggestions? The car has 107k miles and is a 2004.

 

This has come up before, and if I remember correctly those sensors are OK and another fault causes it.
Clear the codes and see if it comes back.

Go to the 2004 Repair Manual 9-162 and see possible causes, which are:
O2 SENSOR SIGNAL CIRCUIT OPEN
O2 SENSOR SIGNAL CIRCUIT SHORT TO GROUND
O2 SENSOR GROUND CIRCUIT OPEN
ENGINE EXHAUST LEAK
O2 SENSOR
POWER TRAIN CONTROL MODULE

 

I had the PO154 code. replaced the sensor but the CEL kept coming on. Finaly found an exhaust leak (two loose bolts at the downpipe) on bank 2 side and repaired it. Light went out and hasn't returned . Guess I now have a spare sensor.

 

So all you did was retighten the bolts and that was it?

 

Yes, that is apparently what fixed the problem. We had replaced the sensor with no luck and then on Rob at Needswings suggestion changed out the oposite side sensor we knew was good and the code was still there. After scratching our heads for several weeks, tracing the sensor wires and other fun stuff, the exhaust leak became so loud with the hood open it sounded like open cut outs. Took the car to the muffler shop and they found and fixed the problem. The next day when I started the car for the first time the CEL was gone. It has been a month and it has not returned. good luck.