Blazer Forum - Chevy Blazer Forums - Insighta into cause of p0420 error

Blazer Forum - Chevy Blazer Forums (https://blazerforum.com/forum/)

- 2nd Generation S-series (1995-2005) Tech (https://blazerforum.com/forum/2nd-generation-s-series-1995-2005-tech-41/)

- - Insighta into cause of p0420 error (https://blazerforum.com/forum/2nd-generation-s-series-1995-2005-tech-41/insighta-into-cause-p0420-error-79023/)

I'd get a scan tool with a data display and see what the o2 sensors are saying. Or find someone how can do it for you. But ya, I agree with above that these codes are simple. If its not the downstream sensor then it's the cat, sorry but it's wasted money to just replace all the sensors.

It's not as simple as a faulty sensor or converter. Any one or more of several things can set a P0420. Here is the flow chart: https://blazerforum.com/forum/diagno...plained-19820/

Quote:

Originally Posted by Captain Hook (Post 595898)

I replaced mine with a Magnaflow direct fit, seems like it was $125. Been on there just over 3 years and 40K miles. Knock on wood, no problems.... yet. I agree on the el cheapo universal jobbies, they're junk. The direct fit converters bolt right on, and are a breeze to replace, no welding involved.

There has to be a reason that the P0420 set. Follow the flow chart step by step and you'll find the problem. If everything checks ok, the converter capacity is probably under sized for the engine.

EDIT: If there were a problem with the MAP sensor, it would have set a DTC for the MAP sensor.

i had my exhaust leak fixed today (stolen cat) and on my way home my SES light came on (which i kinda expected) i stopped off at autozone and had them scan it to confirm my suspicions and yepp P0420. i was under the influence it needed to be welded on could you explain how to bolt it on? i gotta put a cat on to clear the light. do you have a link to the Magnaflow cat Captain Hook? i have a sawzall so i can chop off the straight pipe and maybe fix this myself

sky_blazer, On 2000, the direct fit converter is part of the "Y" pipe. There are universal ones available, and they really should be welded on. If you use clamps it will most likely leak, which could set the P0420 ;)

Quote:

Originally Posted by Captain Hook (Post 615462)

i gotcha now i looked on ebay and saw direct bolt on have flanges to bolt on, i looked under my blazer and whoever cut the cat off cut the flanges off as well which makes my job harder looks like im going universal, but i cant weld

Take it to a muffler shop, they can weld it in for you. Universal converters are rated to handle up to a certain cubic inch engine displacement. Make sure you get one that will handle more than 262 cubic inches or you'll likely see the P0420 again.

Quote:

Originally Posted by Captain Hook (Post 615501)

ok thanks i plan on ordering a universal from either autozone or ebay, ill have to get another downstream o2 sensor to while im at it. BTW until i can order this stuff will i experience poor mileage? or are those the ones in front of the catalytic convertor? also what kind do i need? i keep seeing certain state emissions for them

Downstream oxygen sensors do not affect engine performance, or mileage. They are there to monitor the converter, that's it. AC Delco and Denso sensors have the fastest reaction time, and Denso sensors are cheaper. If the thieves took the oxygen sensor bung, (the thing that the sensor screws into) you'll need a new one of those too. It gets welded into the pipe behind the converter.

Quote:

Originally Posted by Captain Hook (Post 615517)

i still have the bung so i also have the flange the bolts to the muffler too would you still suggest a universal type and have it welded in? i might be able to buy a direct bolt in unit, chop off the front flange, get an exhaust coupler, clamp the front on, and bolt the back on. ill probably experience exhaust leaks though right?

The system needs to be sealed, (no leaks) from the engine to the aft converter sensor. If there are any leaks, the P0420 could be set.