Ses P0420
06-07-2008, 09:07 PM
#1
Staging Lane
Thread Starter
Join Date: Nov 2007
Posts: 66
Likes: 0
Received 0 Likes
on
0 Posts
Ses P0420 I have a 2000 firebird with a 3.8L and the darn thing has been throwing the p0420 code for 6 months now. I have replaced the Cat with a magnaflow highflow model and it did nothing and I have also replaced the O2 sensor. Neither helped. What else could it be???
06-08-2008, 03:24 AM
#2
On The Tree
iTrader: (2)
Join Date: Feb 2006
Location: ATX
Posts: 149
Likes: 0
Received 0 Likes
on
0 Posts
Here ya go...
P0420
CIRCUIT DESCRIPTION
To control emissions of Hydrocarbons (HC) , 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 HC 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 catalysts ability to control emissions. The PCM monitors this process using a Heated Oxygen Sensor (HO2S) located in the exhaust stream past the three-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 conditions for engine warm up. Use the scan tool catalyst data list in order to verify the following.
No VSS, EVAP, Misfire, HO2S, EGR, ECT, MAF, ETC, IAT, MAP, CMP, CKP sensor, Fuel Trim, or Fuel Injector DTCs set.
Engine has been running longer than 10 minutes.
Engine Coolant Temperature (ECT) is more than 76°C (169°F) and less than 124°C (255°F).
Baro is more than 75 kPa.
Vehicle is in Closed Loop.
Intake Air Temperature (IAT) is more than -20°C (-4°F) and less than 100°C (212°F).
Battery voltage more than 10.7 volts.
Warm up the catalyst.
Fully open hood.
Transmission is in park (automatic) or neutral (manual).
Set the parking brake.
Press and hold service brake.
Each time the engine is started the diagnostic can run up to 18 times. After the ten minute run time, and before the diagnostic runs the first time, the engine must run an additional 5 minutes between 1500 and 2000 RPM. Any additional tests on the same key cycle, the RPM must be between 1500 and 2000 RPM for 1 minute.
To activate the diagnostic: Return to idle and put the vehicle in drive (automatic) or depress the clutch (manual).
Test the catalyst.
Place the transmission in drive (automatic) or neutral and depress the clutch (manual).
Within 60 seconds the air fuel ratio will go rich below 14.1 for up to 5 seconds , then it may go lean above 15.3 for up to 6 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 catalysts oxygen storage capacity is less than a threshold considered acceptable.
ACTION TAKEN WHEN THE DTC SETS
The PCM will illuminate the Malfunction Indicator Lamp (MIL) during the first trip in which the diagnostic test has been run and failed.
The PCM will store conditions which were present when the DTC set as Freeze Frame/Failure Records data.
CONDITIONS FOR CLEARING THE MIL/DTC
The PCM will turn the MIL OFF during the third consecutive trip in which the diagnostic has been run and passed.
The History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
The DTC can be cleared by using a scan tool.
DIAGNOSTIC AIDS
Inspect for the following:
The PCM WILL NOT ENABLE the catalyst test until following conditions are met:
Engine speed is plus or minus 250 RPM from desired idle.
Throttle Position (TP) is less than .5 percent.
Short term integrator is between -20 percent and +20 percent .
The catalyst test WILL ABORT if the vehicle falls out side the conditions listed below while the test is running:
Engine speed is plus or minus 250 RPM from desired idle.
Throttle Position (TP) is less than .5 percent.
Short term integrator is between -20 percent and +20 percent.
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 return to step 3 in the table then repeat the test.
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.
The number of attempted tests is limited to 18 per key cycle.
More than 6 tests may have to be attempted 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 then turn the key OFF for 30 seconds . Start the engine 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.
IMPORTANT: Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.
Poor terminal connection. Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Use a corresponding mating terminal to test for proper tension. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Diagrams.
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 may indicate the location of the fault. Refer to Wiring Repairs in Diagrams.
Inspect the PCM and the engine grounds for clean and secure connections.
If the DTC is determined to be intermittent, reviewing the Failure Records can be useful in determining when the DTC was last set.
P0420
CIRCUIT DESCRIPTION
To control emissions of Hydrocarbons (HC) , 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 HC 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 catalysts ability to control emissions. The PCM monitors this process using a Heated Oxygen Sensor (HO2S) located in the exhaust stream past the three-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 conditions for engine warm up. Use the scan tool catalyst data list in order to verify the following.
No VSS, EVAP, Misfire, HO2S, EGR, ECT, MAF, ETC, IAT, MAP, CMP, CKP sensor, Fuel Trim, or Fuel Injector DTCs set.
Engine has been running longer than 10 minutes.
Engine Coolant Temperature (ECT) is more than 76°C (169°F) and less than 124°C (255°F).
Baro is more than 75 kPa.
Vehicle is in Closed Loop.
Intake Air Temperature (IAT) is more than -20°C (-4°F) and less than 100°C (212°F).
Battery voltage more than 10.7 volts.
Warm up the catalyst.
Fully open hood.
Transmission is in park (automatic) or neutral (manual).
Set the parking brake.
Press and hold service brake.
Each time the engine is started the diagnostic can run up to 18 times. After the ten minute run time, and before the diagnostic runs the first time, the engine must run an additional 5 minutes between 1500 and 2000 RPM. Any additional tests on the same key cycle, the RPM must be between 1500 and 2000 RPM for 1 minute.
To activate the diagnostic: Return to idle and put the vehicle in drive (automatic) or depress the clutch (manual).
Test the catalyst.
Place the transmission in drive (automatic) or neutral and depress the clutch (manual).
Within 60 seconds the air fuel ratio will go rich below 14.1 for up to 5 seconds , then it may go lean above 15.3 for up to 6 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 catalysts oxygen storage capacity is less than a threshold considered acceptable.
ACTION TAKEN WHEN THE DTC SETS
The PCM will illuminate the Malfunction Indicator Lamp (MIL) during the first trip in which the diagnostic test has been run and failed.
The PCM will store conditions which were present when the DTC set as Freeze Frame/Failure Records data.
CONDITIONS FOR CLEARING THE MIL/DTC
The PCM will turn the MIL OFF during the third consecutive trip in which the diagnostic has been run and passed.
The History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
The DTC can be cleared by using a scan tool.
DIAGNOSTIC AIDS
Inspect for the following:
The PCM WILL NOT ENABLE the catalyst test until following conditions are met:
Engine speed is plus or minus 250 RPM from desired idle.
Throttle Position (TP) is less than .5 percent.
Short term integrator is between -20 percent and +20 percent .
The catalyst test WILL ABORT if the vehicle falls out side the conditions listed below while the test is running:
Engine speed is plus or minus 250 RPM from desired idle.
Throttle Position (TP) is less than .5 percent.
Short term integrator is between -20 percent and +20 percent.
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 return to step 3 in the table then repeat the test.
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.
The number of attempted tests is limited to 18 per key cycle.
More than 6 tests may have to be attempted 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 then turn the key OFF for 30 seconds . Start the engine 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.
IMPORTANT: Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.
Poor terminal connection. Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Use a corresponding mating terminal to test for proper tension. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Diagrams.
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 may indicate the location of the fault. Refer to Wiring Repairs in Diagrams.
Inspect the PCM and the engine grounds for clean and secure connections.
If the DTC is determined to be intermittent, reviewing the Failure Records can be useful in determining when the DTC was last set.
