[rasterman]

My 99 subaru outback was rear ended causing bumper, body and frame damage (still driveable). A few days later the CEL came on and shows P0420 Catalyst System Efficiency Below Threshold. There's no obvious external damage to the converters. My question is could the impact have caused the cat failure and therefore be added to the damage claim? What evidence might confirm this? I'm the second owner and have receipts that show the original converters (front and rear) were replaced under warranty at 25,000 miles in 2001. The car now has only 68000 miles. Shouldn't they have lasted much longer? Thanks for any guidance.
Bill

Don't assume the cats have failed. The error message just means the car can't tell if they are working right, so it may be just a sensor or yet another problem. Find and read cardoc's P0420 diagnostics thread before spending money.

A rear end hit can include the tailpipe and muffler, and when they get shoved out of the way in a collision the stress can be transferred forwards through the mid pipe to the cats and sensors near the front. So whatever the problem actually is, yes there is a chance it is related to the hit.

It could be as simple as an air leak in the exhaust near the front, and the leak could well be from the hit.

 

[idosubaru]

Doubtful it was caused by the accident unless it was rusty and the impact broke a rusted flange or exhaust hanger - they usually rust where the bracket is welded to the pipe and an impact could break the already weakened rust area. But you would likely hear the leak.

Other than that - If the catalyst came loose maybe...but highly unlikely and without hours of investigation of a very trained person cutting it open and inspecting you'll likely never know...the burden of proof would lie on you for such an obscure possible failure...and you're not going to pay someone hundreds of dollars for a low percentage maybe. If people could get insurance to pay for all those things then you could argue the struts were strained due the impact, the stereo and electronics likely saw voltage peaks during the impact...etc...it's not nearly as black and white as one might think...

The P0420 code is a joke - you can search for it on any forum or google and there's an ocean of debacles because of it.

Install a $5 spacer from Ebay and be done with that code. wasting time wrestling with it is plain silly and there's nothing to gain from it. That sensor is not used by the engine for fueling/driving/operation....so it's useless. Indeed you can literally cut it off the car and it will have zero effects except a check engine light.

 

[AWDFTW]

A hit that causes bumper, body, and frame damage probably broke something in the exhaust system. Your cats are almost certainly fine, but the exhaust needs to be gone over for damage and leaks.

 

[billr10000]

Hi all,
Thanks for the advice. I reset the check engine light by disconnecting the battery and lo and behold the light is out. Might have been the gas. I did a fill up just before resetting.
Thanks again for all the help.
Bill