oxygen sensor replacement

Hi,

O2 sensors are often available as an OEM replacement (includes factory connector) or a universal style (where you splice the wire.) Avoid the universal style whenever possible--the length of the wire and integrity of the connection are problematic in some apps. Hope the one you got is the OEM style.

Dunno about your car, but the older Subies used the screw in style sensor. It requires a spark plug type socket to remove easily. The socket has a slot in the side to allow the wire to be pushed out of the way. Auto parts stores have 'em--they're not that expensive.

The sensors sometimes get almost frozen in place. Warming the exhaust sytem (doesn't have to be real hot) often helps you break the old sensor loose.

When installing a new screw-in sensor, some anti-seize compound should be used on the threads. Many sensors ship w/ the compound already smeared on the threads. Make sure you DO use some a/s compound or you'll REALLY get the frozen sensor blues next time you try to remove one.

Many people put a bit of dielectric grease on plug-in electrical connections when they install new bits. Subaru even suggested it at one time as they were having corrosion problems w/ some underhood connectors. A caution, though: I used to subscibe to a newsletter that had "topic of the month" kinds of info. In one, the author warned against using any grease or other substance on O2 sensor connections. The reason was the insulation on a lot of the wires is extruded w/ tiny air vents lengthwise thru the plastic (for temperature control), and foreign substances in the connectors can clog them. The cooling effect is compromised, w/ attendant errors in reading the voltages by the ECU, which might result in running problems.

Good luck!

Rick

What code did you get. Did you try clearing the CEL and see what code , if any , came back? How many miles on the car. How do you know the rear sensor is bad?

Carl

the car has 137,000 miles on it. Dont know any codes, figured that it was time to change the sensors. starting with the rear one because the rear one is the cheaper of the 2.

I know, I should get a scan gauge.

You can get a scan code reader cheap ($50) from change2e85.com.

Usually, the front sensor will go bad before the rear. It is hotter and exposed to somewhat more corrosive gasses I think. 137k is a lot of miles for the original sebsors and changing them 'preventively' is not stupid, but may not strcitly be required. Is your CEL on? Often, parts suppliers like Autozone, carQuest and others will scan the car at no/little charge. Even a friendly nechanic might do so on a slow day for a coupla lotto tickets. If you get the codes read, post them and someone here may be able to point you in the right direction. Is the car running poorly/bad mileage?

Carl

CEL is on and has been on for some time now. I am changing for a couple of reasons:

1. Why not? Not that expensive. 2. Gas prices. 3. Gas mileage is lower than it was when we first got it (bought it new).

I do realize that mileage will go down as a car gets older, I do recall getting either over 30 or closer to it. Right now I am getting

There are quite a few sensors that could affect gas mileage. A NOTORIOUS one is the Engine Temp Sensor (not the coolant gauge sender).

When were the plugs changed? Could the injectors be dirty? Is the cat. converter. partially clogged? Is the MAF bad/intermittent?

whatever

Carl