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O2 Sensor removal

On a 2003 Subaru Forester: My check engine light came on and my mechanic diagnosed 2 O2 sensors failing. In the process of beginning the repair/replacement, he called to tell me that in order to remove the sensors, the threads would be stripped and it would require replacement of the entire catalytic converter. He said this is common and not unique to Subaru, as they rust, causing the difficult removal. In addition, these were “coming out at an angle”. Has anyone heard of this? Is there a way to remove these sensors without destroying the catalygic converter??

If this vehicle has <80,000 miles have a Subaru dealer do the work. If they damage the cat converter they will replace it likely since its covered by warranty. You will get charged for the two O2 sensors + labor. They also maybe more experienced in the matter.

Depending on which O2 sensor codes showed up there are MANY possibiliies.

Did your mechanic pull an O2 sensor:

rich code
lean code
slow response code
circuit code?

It makes a big difference on what needs to be repaired.

Is this a V-6 or 4 cylinder?

Ask your mechanic which trouble code he retrieved.

The O2 sensors can be remove without damaging the threads by taking a torch and heating up the bungs they thread into before removal. And if the threads are damaged, there’s a tool called a sparkplug thread chaser that restores the threads.


I agree w/ Tester. You should not need to replace anything except the O2 sensors if you’re replacing them… a mechanic who says something like that to start before the work has started is just prepping you for the rip off they are about to give you.

I replaced the O2 sensors on a 1997 Town Car with 256K miles on it, they were frozen solid, but a few minutes with a torch and I was able to replace them both… and I’m basically a novice!

Thanks for your responses! They were very helpful and confirmed my suspicions about the mechanic. I have scheduled an appt with the dealer to look into it and since I have an after-market warranty the O2 sensors replacements will be covered there for a small deductible. Then, as amdrew j suggests, if the dealer damages the converter, they hopefully would replace it under the manufacturer’s warranty. Thanks again!

A torch in the right hands is a powerful tool.

If you would ever attempt this yourself soak the threads with PB Blast and try to remove with the engine cold.