Question about 1999 Chevrolet Blazer
There are a couple of things to consider here. That code indicates that the O2 sensor behind the cat is not functioning like the engine computer expects-either the cat itself is not functioning properly or you may have an exhaust leak, or the heater circuit in the O2 sensor is faulty. The cat should get up to 600 degrees and it burns unburned fuel before ti gets to the 2ed O2 sensor-if it cannot do this, the CEL comes on and you have a P0420. Before replacing the cat, clear the code and see if it comes back-if it does, you might try first replacing the O2 sensor. If that doesn't work, get a 'oil fouler' spark plug adapter and install the O2 sensor in it, then install both into the exhaust-this 'shields' the tip of the O2 sensor and slows it down, fooling the engine computer into seeing it switching slowly, as it is supposed to do. Your only other choice is to replace the cat, and an aftermarket cat is much less than an OEM unit.
By the way, if you have burnt valves, a P0420 is the least of your worries.
Posted on Apr 01, 2011
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Posted on Jan 02, 2017
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