Need some help or advice on a P0421 code on a 2ZZ swap

292 Views 9 Replies 3 Participants Last post by dev, 8 d ago

Alphagamma

Discussion Starter · 13 d ago

History: Recently bought a 2001 with a 2zz swap that was done in California AND it was done legally passing inspections. It has a 2001 Celica GTS driveline with transmission. The header used, to legally pass emissions, was the 1zz header with a 2zz flange welded on. Incidentally the CATs in the header were gutted and it still passed. It was using the stock 1zz midpipe with CAT. When I bought it, there were NO engine codes and I drove it for about a 1000 miles before making any changes.

I purchased and installed the PPE header for the 2zz and a new high-flow CATed PPE mid-pipe. Now, I get the P0421 code, which surprised me. I double checked everything I can think of. I can't find any exhaust leaks, the O2 Sensors are correctly plugged in and wired. I even tried a new downstream 02 sensor.

I'm baffled, as I went from a catless header to a catless header and a CATed mid-pipe to a CATed mid-pipe. What am I missing?!?!?

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dev

· #2 · 12 d ago

Hi flow cats are notorious for this code. Some cause the code immediately or it can happen in time. The OEM cat is better at being a catalyst but it is also more restrictive for this reason.
What you can do is use a non fouler to space out the O2 sensor so it takes a less concentrated reading of the gasses to satisfy the ECU.
Good luck

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Alphagamma

Discussion Starter · #3 · 12 d ago

I was wondering if that might be the issue, but didn't expect it with a brand new CAT from a company known for quality. I'll see if I can find a spacer, these parts are harder to find than they used to be due to government enforcement.

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dev

· #4 · 12 d ago

Alphagamma said:
I was wondering if that might be the issue, but didn't expect it with a brand new CAT from a company known for quality. I'll see if I can find a spacer, these parts are harder to find than they used to be due to government enforcement.

The ironic thing is the PPE high-flow or others like those that use quality high flow cats sourced from Magnaflow have this issue but the cheap Chinese high-flow downpipe that has poor fittings does not. It’s possible the spacing on the bung could be thicker might be the reason but who really knows.

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dblotii

· #5 · 12 d ago

I can recommend the GESI catalytic converter from Verocious. High flow, metal substrate and good enough for California standards

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Alphagamma

Discussion Starter · #6 · 11 d ago

I ordered a Spacer that should hopefully arrive before the weekend. I'll let you know how it goes.

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Alphagamma

Discussion Starter · #7 · 9 d ago

Well. The spacer did not help. I get the P0421 code within a few minutes of driving the car. Any other ideas?

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dev

· #8 · 9 d ago

You will have to do a little exploring to find other solutions. There use to be 02 simulator devices that became illegal but still possible to purchase and some other resistor hacks. Apart from that you might have to weld in a different cat.

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Alphagamma

Discussion Starter · #9 · 8 d ago

dev said:
You will have to do a little exploring to find other solutions. There use to be 02 simulator devices that became illegal but still possible to purchase and some other resistor hacks. Apart from that you might have to weld in a different cat.

I had a hunch that might be the answer. I might just leave the light on the dash as I have this car registered in a county that does not do emissions checks.

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dev

· #10 · 8 d ago

Alphagamma said:
I had a hunch that might be the answer. I might just leave the light on the dash as I have this car registered in a county that does not do emissions checks.

It can get a bit tricky. If I was in the same situation which I thought I might be with a sports cat I would want it solved because if you develop a code of any significance you will not know.

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