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Re: P0420 but I think its the pre-cat 02 sensor Posted by SWEDECAR [Email] (#112) [Profile/Gallery] (more from SWEDECAR) on Wed, 16 Dec 2015 07:52:37 In Reply to: P0420 but I think its the pre-cat 02 sensor, Nigel near Boston, Wed, 16 Dec 2015 07:40:12 Members do not see ads below this line. - Help Keep This Site Online - Signup |
P0420 is almost always a dead give away for a bad cat.
Nowadays when many front sensors are of a fuel/air ratio nature, you might not see the old style voltage swing up and down between 0V and 0.8V but more of a flat line around 1.00
The rear sensor though are many times still an old style sensor with the voltage swing.
So if the front sensor stays around 1.00 and the rear is going up and down between 0 and 0.8V, it is a pretty good indication that the cat is bad.
If you as you said had an IDM failure that died while cruising (kind of rare on these newer Saab's unless it is an aftermarket IDM) you probably killed the little pre cat.
Anders
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