Pathart500

Lately, I turn on my 03 A4 1.8t and the blowers come on immediately and stay on. The temp gage will not move no matter how long I drive it. A few days later the CEL came on and I had a couple of misfires when the RPM were about 2500. I had the codes pulled and this is what I got:

P0141 - Heated oxygen sensor Bank 1 Sensor 2 (H02S12)
P3081 - Engine temp too low
P0304 - Cylinder 4 misfire condition

Question 1: What is the Heated Oxygen Sensor where is it and what does it do?

Question 2: Can a bad thermostat (failed in the open condition) cause the ECT to not heat up?

Question 3: Can either a bad Heated oxygen sensor or a low engine temp cause a misfire?

lyleswk

So 2 qestions: 1) "blowers" are the 2 fans mounted behind the radiator? 2) Also, what sort of reader did you use? VAGCOM or generic "Autozone" reader? Reason I ask is the generic readers don't tell you if fault logged is intermittent in which case you can rule it out as causing a running issue.

Don't know a lot about the V6, but assuming the anwswer to 1 is yes, then it is probably a coolant sensor(s). I do not know where it(they) is(are) on the 3.0, so you will have to do a little more research. If the sensor does not solve it, then the thermostat would be next.

As far as the o2 sensor, I believe the v6 has 4, one before and after each cat on the exhaust. There are used by the ECU to adjust the mixture for emissions purposes Again not familiar with the V6, but I believe "Bank 1" is passenger side and sensor 2 is after the cat. However, I would verify they are not intermittent before I dive into it since o2 sensors can be a bear to replace.

Misfire; I think cylinder "4" is the one near the firewall on the driver's side. If you continue to get misfires, call an Audi dealer and see if you have had the col packs replaced under warranty. If yes then swap and see if it follows the coil pack.

Pathart500

Yes, the blowers I am referring to are the fans directly behind the radiator. I used the Autozone OBDII reader.

Pathart500

Oh, I do not have the 3.0 V6. I have a 2003 1.8t A4 Quattro.

lyleswk

Yeah, you clearly say you have a 1.8t in your post; I got locked in on the "Bank 1" in the error code.

Anyway, the combination of the fans running and temp gage not reading correctly is generally the "green" sensor at the back of the engine bay. Quick swap and it should solve those problems. As far as the misfire, I would see if it occurs again once you replace the sensor. The sensor does provide input to the ECU, so it is possible it caused the misfire.

Below is a link to a source of the sensor. I would purchase a new c-clip and o-ring to be on the save side.

http://www.ecstuning.com/Search/Site.../Green_Sensor/

As far as the 02 sensor in question, it is the sensor after the cat. If you look just past the turbo, you will see the precat O2 sensor. Follow the exhaust on down past the cat and you will see O2 sensor that threw the code.