O2 Sensor Issue

[Winterman]

We have 96 Outback with 112K and the "Check Engine Light" went on. Took it to our Mechanic and it was the O2 and Cam Sensors and replaced them.

 

That lasted about a day or two and the O2 Sensor failed again, to which the Mechanic replaced for free. The new O2 Sensor died.

 

Anybody know of a problem causing O2 Sensors to fail in 96 Outbacks? (It's a 2.2 liter, 5spd)

 

Thanks!

[SevenSisters]

Not exactly sure how the new cars with OBDII work, but could the sensor be reporting some out of range condition caused by some other system, eg fuel or cat?

 

If not, could be a bad ECU or connection.

[ron917]

If it's any consolation, I'm fighting the same problem in one of my other cars. ECU keeps saying the O2 sensor is bad, even with a new one. Evidence points to a lean mixture (failed smog test with high NOx). Probably a vacuum leak, but I haven't found it yet.

 

I don't know the specifics of your ECU, but many will throw a bad O2 sensor code if the reading from the sensor doesn't vary enough. In normal operation, the sensor reading varies regurlarly, as the the ECU fine tunes the mixture - it swings between slightly rich and slightly lean.

 

A bad sensor won't vary it's reading. An overly rich or lean condition that is too far out of range for the ECU to correct will cause the same symptom. A rich mixture may also coat the sensor with soot, which will prevent it from working properly.

 

It's highly unlikely that you got two bad, new, O2 sensors. I'd look for vacuum leaks and bad connections first.

[state]

I'm still fighting a CEL light on my 95 Legacy Wagon too. My code is P0170. Fuel trim malfunction. I checked alldata.com and it said 1- check for air intake leak, 2- check for exhaust leak, 3- fuel pressure, 4- coolant temp sensor, 5- Mass air sensor. Before I looked at Alldata, the first mechanic said it was the front o2 sensor. I replaced it and the CEL came back the next day. About 60 miles later. Took it back to him and he said it might be the ECM. Lost confidance in him. Took it to another mechanic, he said it was the rear o2 sensor. I replaced that and it came back a couple of days later. I know it's the same code because I bought my own obd II reader. I'm going to check my fuel pressure next and if that's not it I'll probably replace the Mass air sensor. Have checked the other things the best I can and I think they are OK.

[Winterman]

Wow.

 

This is a great site. I'll see if one of these tips work a let you all know what was wrecking the O2 Sensor.

 

Thanks Everybody.