p0420 and high flow cat

[irondiezl3]

i read all the other posts i have a high flow mag cat been on car for 8 months now. never had a code or issue now i have this code came on today. if i change my 02 sensors and this code is still on can my 8 month old cat reallly be clogged that fast? car seems to run fine?

[a.graham52]

is the 420 the efficency code? If so it can also mean ur cats not working at changing the chemicals well enough. Doesnt nessasarly mean its clogged.

[irondiezl3]

yes so its deffinantly the cat if sensors dont change it?

[Mike The Canadian]

I've heard of aftermarket cats doing this...
It's the converter not cleaning the air efficiently..
Don't worry about it unless emissions is coming up!

[mastershake]

if your engine is running rich it could kill the cat converter prematurely

[sleepyalero]

mine has the same problem, but was told that its the o2 sensor behind the cat.

[Redog]

You're probably going to have to bypass it

[irondiezl3]

last month i had bad injectors for a month before they were all replaced idk if that could have ruined the cat that fast.

[unchained01]

you would be suprised and the sensor is next

[irondiezl3]

changed both sensors then cleared the code drove it for an hour after took on highway turned on and off a few times but according to my friend it could take a week of normal driving for the pcm to pop that code back up if its not fixed

[a.graham52]

do you have any exhaust leaks? thos could cause fauly readings i think.

[irondiezl3]

funny u asked that i checked yesterday for leaks didnt see or hear any. i can only hope it was one of the sensors but with my luck its the new cat.

[a.graham52]

i know we have a lot of bad luck with aftermarket o2 sensors. we only recommend gm sensors. but it is possible that cats been damaged due to the injectors but its also possible that the cats just not efficent enough period.

[irondiezl3]

yea i shoulda bought delco 02 sensors i have always had bosch i know better by now :/ i just hope if its not on in a week that it isnt the cat

[mastershake]

i think it's like 3 warm-up cycles with the conditions present to set a code

[a.graham52]

Circuit Description

To control emissions of hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx), a 3-way catalytic converter (TWC) is used. The catalyst within the converter promotes a chemical reaction which oxidizes the HC and CO present in the exhaust gas, converting these chemicals into harmless water vapor and carbon dioxide. The catalyst also reduces NOx, converting the NOx to nitrogen. The TWC also has the ability to store excess oxygen and release the stored oxygen to promote these reactions. This oxygen storage capacity (OSC) is a measurement of the catalysts ability to control emissions. The powertrain control module (PCM) monitors this process using a heated oxygen sensor (HO2S) located in the exhaust stream past the TWC. When the catalyst is functioning properly, the HO2S 2 is slow to respond to a large change in the HO2S 1 signal. When the HO2S 2 responds quickly to a large change in the HO2S 1 signal, the OSC and efficiency of the catalyst is considered to be bad and the malfunction indicator lamp (MIL) will be illuminated if subsequent tests also indicate a failure.

Conditions for Running the DTC

1. Meet the conditions for engine warm-up. Use the scan tool catalyst data list in order to verify the following conditions:

• DTCs P0030, P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0128, P0130, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P0140, P0141, P0171, P0172, P0201–P0206, P0300, P0336, P0341, P0404, P0405, P0410, P0440, P0442, P0443, P0502, P0503, P0506, P0507, P1133, P1134, P1351, P1352, P1361, P1362, or P1441 are not set.

• The engine has been running longer than 10 minutes.

• The engine coolant temperature (ECT) is between 76–124°C (169–255°F).

• The barometric pressure (BARO) is above 75 kPa.

• The vehicle is in Closed Loop.

• The intake air temperature (IAT) is between -20 to +100°C (-4 to +212°F).

• The battery voltage above 10.7 volts.

2. Warm up the catalyst.

• Fully open the hood.

• The transmission is in Park, automatic, or Neutral, manual.

• Set the parking brake.

• Press and hold the service brake.

• Each time the engine is started the diagnostic can run up to 18 times. After the 10 minute run time, and before the diagnostic runs the first time, the engine must run an additional 5 minutes between 1,500–2,500 RPM. For any additional tests on the same key cycle, the engine must be between 1,500–2,500 RPM for 1 minute.

• In order to activate the diagnostic, return the engine to idle and place the vehicle in drive, or depress the clutch pedal for a manual transmission.

3. Test the catalyst.

• The transaxle is in drive, for automatic transaxles, or neutral for manual transaxles with the clutch pedal depressed.

• Within 60 seconds the air/fuel ratio will go lean, below 14.1, for up to 7 seconds. The air/fuel ratio may then go rich, above 15.3, for up to 7 seconds.

• Using the scan tool check and see if DTC P0420 has passed or failed this key cycle.

Conditions for Setting the DTC

The PCM determines that the catalyst's oxygen storage capacity is below a threshold considered acceptable.

Action Taken When the DTC Sets

• The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.

• The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records.

Conditions for Clearing the MIL/DTC

• The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.

• A current DTC, Last Test Failed, clears when the diagnostic runs and passes.

• A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

• Clear the MIL and the DTC with a scan tool.

Diagnostic Aids

Inspect for the following conditions:

• The PCM will not enable the catalyst test until the following conditions are met:

- The engine speed is plus or minus 265 RPM from the desired idle.

- The throttle position (TP) is 1.5 percent or less.

- The short term FT is between −20 to +20 percent.

• The catalyst test will abort if the vehicle falls outside the conditions listed above while the test is running.

Important:: When you use the scan tool to force the cooling fans ON, use the next list and previous list soft keys in order to enter the catalyst data list. If the catalyst data list is not entered this way, the cooling fan control will be canceled.

• The catalyst test may abort due to a change in engine load, i.e., A/C, coolant fan. If this problem occurs, use the scan tool to force the cooling fans ON then return to step 3 in the table.

• The number of attempted tests is limited to 18 per key cycle.

• More than 6 tests may have to be attempted in order to get 6 completed tests. An aborted test counts as an attempted test.

• If 18 tests have been attempted, and a decision has not been made this key cycle, turn the key OFF for 30 seconds, start the vehicle, and perform the Conditions for Running the DTC, including the 10 minute run time.

• After returning to an idle, the HO2S 1 signal may stay rich or lean for several seconds, causing the test to be delayed.

If the condition is determined to be intermittent, refer to Intermittent Conditions .

[irondiezl3]

holy info lol idk what that means but thanks alot for that i have to assume by now ive been past all those since its been on and off like 7 times and benn on highyway and went from cold start to full temp all those times? there is no way im that lucky

[a.graham52]

now ASSUMING you have no intake leaks or exhaust leak, id throw a rear o2 sensor at it (a good gm one) and if the light comes back on then its gotta be the cat.

[irondiezl3]

i changed both 02 sensors last night but not gm ill try gm if it comes back on

[a.graham52]

woah if you did it last night then clear the codes (disconnect the battery for about 10 minutes or longer) and give it a while before going any further.