Code P0420

Good afternoon.

The 420 is for a failed catalytic converter. The precious metals inside the catalytic converter that process the gases is not working anymore. There are a couple of checks you need to do first. I will list them for you.

Check for any exhaust leaks.
If the engine has any misfires or codes for cylinder misfires, check them first.

Roy

CIRCUIT DESCRIPTION
In order to control emissions of hydrocarbons (HO), carbon monoxide (CO), and oxides of nitrogen (NOx), a three-way catalytic converter is used. The catalyst within the converter promotes a chemical reaction which oxidizes the HO and CO present in the exhaust gas, converting them into harmless water vapor and carbon dioxide. The catalyst also reduces NOx, converting it to nitrogen. The converter 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 catalyst's 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 3-way converter. 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 MIL will be illuminated if subsequent tests also indicate a failure.

CONDITIONS FOR RUNNING THE DTC
Meet the conditions for engine warm up. Use the scan tool catalyst data list in order to verify the following.
- DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0130, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P0140, P0141, P0171, P0172, P0201-P0206, P0300, P0336, P0341, P0401, P0403, P0404, P0405, P0410, P0412, P0418, P0440, P0442, P0443, P0446, P0449, P0502, P0503, P0506, P0507, P1133, P1134, P1336, P1351, P1352, P1361, P1374, or P1441 are not set.
- The engine has been running more than 10 minutes.
- The engine coolant temperature (ECT) is above 70°C (158°F) and below 124°C (255°F).
- The barometric pressure (BARO) is above 75 kPa.
- The vehicle is in Closed Loop.
- The intake air temperature (IAT) is above -20°C (-4°F) and less than 100°C (212°F).
- The battery voltage above 10.7 volts
Warm up the catalyst.
- Fully open the hood.
- Place the transmission 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 150-250 RPM.

For any additional tests on the same key cycle, the engine speed must be between 1500-2500 RPM for 1 minute.
- In order to activate the diagnostic return the vehicle to idle and put the vehicle in drive, or depress the clutch for a manual transmission.
Test the catalyst.
- Place the transmission in drive (automatic) or neutral (for manuals with clutch depress).
- VIN K California Emissions- Within 60 seconds the air fuel ratio will go rich below 14.1 for up to 6 seconds, then it may go lean above 15.3 for up to 8 seconds.
- VIN K FED Emissions-Within 60 seconds the air fuel ratio will go lean above 15.3 for up to 6 seconds, then may go rich below 14.1 for up to 7 seconds.
- VIN 1-With in 60 seconds the air fuel ratio will go rich below 14.1 for up to 7 seconds, then it may go lean above 15.3 for up to 9 seconds.
- Check if DTC P0420 has passed or failed this key cycle using the scan tool.

CONDITIONS FOR SETTING THE DTC
The PCM determines that the catalyst's oxygen storage capacity is below an acceptable threshold.

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
Check for the following conditions:
The PCM will not enable the catalyst test until following conditions are met:
- The engine speed is plus or minus 100 RPM from the desired idle.
- The throttle position (TP) is 0.0 percent.
- The short term integrator is between -20 percent and +20 percent.
The catalyst test will abort if the vehicle falls outside the conditions listed below while the test is running:
- The engine speed is plus or minus 125 RPM from desired idle.
- The throttle position (TP) is 0.0 percent.
- Short term integrator is between -20 percent and +20 percent.
The catalyst test may abort due to a change in engine load, for example, from the A/C or from the coolant fan. If this condition occurs, use the scan tool in order to force the cooling fans ON, and return to Step 2 in the table.

IMPORTANT: When using the scan tool to force the cooling fans on use the next list and previous list soft keys to enter the catalyst data list. If the catalyst data list is not entered this way the cooling fan control will be canceled.

More than 6 tests may have to be attempted in order to get 6 completed tests. An aborted test counts as an attempted test. The number of attempt tests is limited to 18 per key cycle. After returning to an idle the HO2S 1 signal may stay rich or lean for several seconds causing the test to be delayed.
A faulty connection at PC-Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection. Use a corresponding mating terminal to test for correct terminal tension.
A damaged harness-Inspect the wiring harness for damage. If the harness appears to be OK, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the display will indicate the location of the fault.

TEST DESCRIPTION

Steps 1-8
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Steps 9-11
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The numbers below refer to the step numbers on the diagnostic table:
1. The Diagnostic System Check-Computers and Controls Systems prompts you to complete some basic checks and store the Freeze Frame And Failure records data on the scan tool.
2. If any component DTCs are set, diagnose those DTCs first. A fault in a component can cause the converter to appear degraded or may have caused its failure.
3. Clearing the DTCs allows the catalyst test to be completed up to 18 times and completed up to 6 times this ignition cycle. If the A/C is not turned off the diagnostic will not run. The engine must be warmed-up. The converter needs to be warmed-up by raising the engine speed above idle for the specified time prior to each attempted test. Check and see if DTC passed or failed this ignition cycle. If the DTC does not pass or fail look for a possible reason that would cause the test to abort.
4. This step includes checks for conditions that can cause the 3-way converter to appear degraded. Repair any conditions found before proceeding with this table.
9. If the 3-way converter needs to be replaced, make sure that another condition is not present which could damage the converter. These conditions may include misfire, leaking or plugged fuel injectors, high engine oil or coolant consumption, retarded spark timing or weak spark. Correct any possible causes of converter damage before replacing the converter.