Got the UG under the tree and have been making great use of it. I have had an intermittent code p1193 that shows up every now and then so I was reading a bit and decided to watch the 02 values on the ride home. Both upstream sensors cycle as they should but both downstream sensors are stuck at 1.020 volts. Now that should mean both downstream sensors are toast right? If they are both gone wouldn't I have a constant CEL and multiple codes popping up? Just trying to figure out if the reading is faulty or if I do in fact need both downstream sensors.

 

The downstream sensors monitor the converters. If everything is working properly, the downstream sensors don't fluctuate like the upstream. when they start fluctuating it tells the ECM that your converters aren't doing their job anymore and will turn your check engine light on (code P0420, or somewhere around that number, I forget). So, nothing is wrong with your aft O2 sensors or your UG

 

Cool that's a relief, what would cause the p1193 to keep showing up out of the blue? When it pops up I can reset the code and it stays away for weeks.

 

1193 is a O2 sensor heater code(don't remember which side, but your scanner should tell you), there is a heater circuit built into the sensor to help the sensor get to operating temperature faster. Usually it is a failure in the sensor itself (this doesn't show up when monitoring operating voltage, totally different circuit) but it could be a wiring problem to the sensor, or a bad connection. What usually sets that code is that the ECU applies power to the heater and if it doesn't see the circuit being completed, it thinks the heating element has burnt out. That particular code doesn't usually come and go, the heater burns out like an incandescent bulb and there is no more continuity through the heater. But it could still be the sensor, I've just never seen one fail in that particular way (intermittent).

 

It is a code for downstream heater, but system won't tell you which side, just one sensor or both. See page 47 of attached GEMS ECU manual.