P0420 code. Chevy Blazer

[dlundblad]

Catalyst efficiency bank 1 below threshold.

I dealt with this code earlier this year. Blindly chucked parts and money at it and put in a new OE 02 sensor. Still came back and finally got a no start condition. Turns out it was the fuel pressure regulator. You could tell it was leaking by how clean the area was. Replaced it with the OE part.

Fast forward to yesterday and it’s back.. Since everything is basically new, I’m guessing it’s the dreaded poppet style injectors assuming the pressure regulator is functioning properly.

Also, bank 1 include either the sensor before or after the cat? I’m guessing no, but figured it was worth the ask.

Thanks guys.

 

[Graham Piccinini]

Bank 1 - driver side, Bank 2 - passenger side. P0420 in my experience was always the sensor after the catalytic converter. Replace the cat converter, or hollow it out and use O2 CEL eliminator spacer for the O2 sensors after the cat. At least that is what works in NC, not sure how your inspections work and if you can get away using the same method.

 

[Merek]

Yes bank 1 is before the converter, I have battled this code with both of my Honda Civic's and so far I've never had to replace the secondary one. I have a code scanner which basically lists the code and a brief description then I get online and search to see what others have done with the same car and typically you're not the only one having that same problem. Generally on mine when a code pops up it's either the p0420 or one of the cylinder misfire codes. With mine the primary is a wide band o2 which has 5 wires and is 2x-3x the cost over the standard one, on both of them I've had to replace those sensors plus the exhaust manifold which the converter is attached so it's an all in one unit.

I would replace the sensor first as it's a lot cheaper than a new cat and go from there. I wouldn't be surprised if the cat been damaged basically poisoned and you'll end up replacing that down the road as well.

I don't know those 4.3's very well, do you have one on each side in the manifold coming off the engine or is it just one before the cat and then another after? I guess if one is in each manifold and another after you would have 3 of those o2 sensors.

 

[Graham Piccinini]

CEL eliminator I am referring to.

 

[dlundblad]

IIRC it has 4 sensors. 1 at each manifold, 1 before cat and 1 after.

 

[slacktide_bitog]

Bank 1 is the cylinder bank. One side is called Bank 1; the other is called Bank 2

Bank 1 Sensor 1 is the sensor in Bank 1 manifold
Bank 2 sensor 1 is the sensor in the Bank 2 manifold

Bank 1 Sensor 2 is the sensor before the cat
Bank 1 sensor 3 is the sensor after the cat

Did you replace the cat? You probably need a new one. Get the Walker #81963

 

[dlundblad]

The cat is a few years old. Ended up using a magnaflow of all things. Since then, it has been through a lot though. Leaking transfer case switch that allowed fluid into the engine as well as the faulty pressure regulator.

 

[slacktide_bitog]

The cat is a few years old. Ended up using a magnaflow of all things. Since then, it has been through a lot though. Leaking transfer case switch that allowed fluid into the engine as well as the faulty pressure regulator.

Is the Magnaflow cat you bought a CARB one? The non-CARB converters only have to last 2 years/25k, whereas California requires a 5 year/50k warranty. The California converters have more catalyst material in them. Magnaflow makes a CARB-approved cat for your Blazer.

 

[dlundblad]

I’d have to double check. It had a lifetime warranty so I’m assuming it’s CARB?

 

[oggb]

Bank 1 - driver side, Bank 2 - passenger side. P0420 in my experience was always the sensor after the catalytic converter. Replace the cat converter, or hollow it out and use O2 CEL eliminator spacer for the O2 sensors after the cat. At least that is what works in NC, not sure how your inspections work and if you can get away using the same method.View attachment 30621

I've heard them referred to as "anti-foulers" too. I was coming to leave the same comment!

Depending on where he lives in IN he might have an emissions testing and/or inspection requirement. Works like a charm for us here in VA, though. As long as you're not in the northern part of the state, anyhow.

 

[dlundblad]

I've heard them referred to as "anti-foulers" too. I was coming to leave the same comment!

Depending on where he lives in IN he might have an emissions testing and/or inspection requirement. Works like a charm for us here in VA, though. As long as you're not in the northern part of the state, anyhow.

Fory Wayne area. No inspection here. I’ll try a new cat.