P0420 Again

[00GTP4ME]

Oh really? Stupid question, but I can't remember; is the u-bend before or after the CAT? It's after isn't it?

[danielsatur]

I would only replace the upstream H02 sensors, because they are used for the Air/fuel mix (feed back) signal.

The down stream H02 sensors are used to check the integrity of your catalytic converters, only replace as needed.

[grandprixgtx00]

Originally Posted by 00GTP4ME

Oh really? Stupid question, but I can't remember; is the u-bend before or after the CAT? It's after isn't it?

it is post cat (after the cat)

[00GTP4ME]

Originally Posted by danielsatur

I would only replace the upstream H02 sensors, because they are used for the Air/fuel mix (feed back) signal.

The down stream H02 sensors are used to check the integrity of your catalytic converters, only replace as needed.

Could it be that my CAT is completely fine and I just have a bad post-CAT O2 sensor?

I do have an infrared thermometer, so if someone can confirm the correct procedure to test the CAT, I can probably do that tonight and see what I get.

BTW, I cleared the code just to see how bad things really are. My guess is that if a component is in really bad shape, the code should kick back on fairly quickly. (CEL stayed off on my drive to work this morning).

Originally Posted by grandprixgtx00

that is where i purchased the Ubend delete for both my GT and SE. i purchased mine WITH the rear o2 instead of using the bung. i also have a res delete on my GT, and have not had any codes since it was installed.

Is the only difference between the two is that with one, there was an O2 sensor in the box when you opened it (or maybe it was pre-screwed in the bung for you? )? The actual apparatus is still the same regardless if you get the bung version or the "WITH O2 sensor" version, right? With the bung, you just screw in whatever O2 sensor you end up getting, right? I'm not sure what the difference is you're going after.

[grandprixgtx00]

the difference is simply the one with the o2 has the threads that you screw the sensor in. the one w/o is just a straight pipe, no hole for the o2

edit: the bung does not screw in. it just pretty much hangs there.

[00GTP4ME]

Oh, ok that makes sense. Thanks man.

Well I'm going to go ahead and try testing the pipe temp right before the cat and right after the cat and just see what happens. I'm not too clear on what I should expect to see, but I guess I can worry about that after I have my readings.
I drove the car around all day yesterday and the light never turned back on. I hope it's something I have some time with before I'm pinned in to making a repair.

So based on all feedback I've got so far (thank you all), I'm going to stick with an OEM cat, u-bend delete probably won't cause issues as long as I get one that will allow for a post-cat O2 sensor, and don't worry about replacing the post-cat O2 sensor for now. Right?

[tblake]

Originally Posted by 00GTP4ME

....u-bend delete probably won't cause issues as long as I get one that will allow for a post-cat O2 sensor

If you are lucky.....

Any sort of aftermarket exhaust work can sometimes trip the P0420 for no apparent reason (high flow cat, aftermarket cat, larger diameter pipes, u-bend, headers....).

If you get the exhaust work done and the P0420 still trips on occasion, let me know. Maybe we could figure out a way to get your code P0420 deleted with my powertuner.

I've got all my rear O2 sensor codes deleted so escentially I could unplug my rear O2 sensor and no codes would trip. The sensor is just there for looks , but I do still have a high flow cat. We all have to do our part to protect the environment..

[danielsatur]

My understanding only 15 states practice Federal emisssions, who really cares?
CA. residents can smoke, but there cars cant!

[00GTP4ME]

Originally Posted by tblake

If you get the exhaust work done and the P0420 still trips on occasion, let me know. Maybe we could figure out a way to get your code P0420 deleted with my powertuner.

Dude, you need to move to Utah. It's way too cold there! Bob found his GXP here! What more reason do you need? We can drag our GTP's one weekend and then take the girls out for some 4x4 in the mountains the next! And then your powertuner would be right where I (we ) need it!

The whole point of the rear O2 sensor is just to let you know if your cat is working properly, right?

What do you think about what I said here:

BTW, I cleared the code just to see how bad things really are. My guess is that if a component is in really bad shape, the code should kick back on fairly quickly.

Do you think that's a safe assumption to make?

Originally Posted by danielsatur

My understanding only 15 states practice Federal emisssions, who really cares?
CA. residents can smoke, but there cars cant!

I think Utah is one of them. I probably shouldn't complain though. Utah (Salt Lake City & Logan to be specific) have the officially worst air quality in the country so I'm sure not letting it get worse than it already is is probably a good thing (it's all those $*%& chipped diesels.)

[tblake]

I'm totally there! Wish I could afford it!

You are probably right on your assumption. I think it takes 3 consecutive drive cycles of a failed cat code in order for it to trip a P0420.

My P0420 was coming on every other day at most. I just kept my acctron code reader in the back seat to erase the code when the light came on. It just got old so I just deleted the code.

Chipped diesels! HAHA! Yeah they rip good, but you can see the unburned raw fuel drip from the tailpipe.

[00GTP4ME]

What is a "drive cycle?"

[danielsatur]

Who was thinking about being green with Ford Mustang, Chevy Camaro, and Dodge Challenger?

What about installing some O2 simulators down stream.

[BNaylor]

Originally Posted by 00GTP4ME

What is a "drive cycle?"

See the thread below going back to 2007.

Click here

Originally Posted by BNaylor

I would take the DTC at face value and replace the CAT convertor. The CAT has deteriorated and operating below the required threshold when the PCM looks at both the front and rear 02 sensors to make a determination. Plus there are alot of variables as to when that specific DTC will set so it may not set every drive cycle or on a specific trip. See some engine parameters below:

- Engine speed is 1,410- 3,100 rpm.
- Calculated TWC temperature in PCM is above 574 °C {1065 °F}.
- Calculated load is 15- 50% (at 2,000 rpm)

On my Actron scanner DTC P0420 shows up as a pending code. From what I understand the SES/CEL MIL illuminates if the PCM detects the above malfunction conditions in two consecutive drive cycles or in one drive cycle while the DTC for the same malfunction has been stored in the PCM. DIAGNOSTIC MONITORING TEST RESULTS and PENDING CODE are stored if PCM detects the above malfunction condition during first drive cycle.

Hope the info helps.

[BNaylor]

The P0420 code is a "Type A" DTC. See below.

Originally Posted by BNaylor

PCM Basics & Diagnostics 101:

There are 4 types of DTC error codes by category:

Type "A" - Emissions related, turns on MIL (SES) light the first time DTC sets.

Type "B" - Emissions related, turns on MIL (SES) light if fault is active for 2 consecutive driving cycles.

Type "C" - Non-emissions related, does not turn on MIL (SES) light but may turn in SERVICE VEHICLE SOON light.

Type "D" - Non-emissions related, does not turn on MIL (SES) light or SERVICE VEHICLE SOON light.

There are two category of failures hard and intermittent.

A hard failure will cause the MIL light to turn on and remain on until the malfunction is repaired.

An intermittent failure may cause the MIL light to flicker or glow and go out (flash) about 10 seconds after the intermitent fault goes away. However, a corresponding DTC will be retained in PCM memory. If a related fault does not occur in up to 50 drive cycles (engine starts) the DTC error code will be erased from memory by the PCM.

Certain DTC error codes classified as "A" are hard and normally will not reset or cure themselves. It will require a reset after review of the error code and corrective action. However, there are certain class "A" DTC error codes after corrective action is taken and when the PCM runs the test that will erase themselves and turn off the MIL (SES) light. Evaporative emissions codes are a good example. Loose gas cap P0440 - 0442.

Codes classified as "B" may clear themselves after a predetermined drive cycle but it varies.

GM categorizes DTC codes and you need to review the Master Code or Mode 6 code listings for your specific year, model and make of vehicle. A GM service manual will contain all DTC error codes applicable to your vehicle. The code description will contain what class the DTC error code is.

[00GTP4ME]

Thanks Bob!