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For 1990-2009 cars only
Makes 🢒 Oldsmobile 🢒 2000 🢒 Intrigue 🢒 Engine 🢒 Engine Controls - 3.5L 🢒 DTC P0420 Catalyst System Low Efficiency

Circuit Description

In order to maintain a reasonably low emissions of hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx), a three-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. This reaction converts them into harmless water vapor and carbon monoxide. The catalyst also reduces NOx, converting it to nitrogen. The powertrain control module (PCM) monitors this process via the post catalyst heated oxygen sensor (HO2S) signal. The post catalyst HO2S, located in the exhaust stream after the TWC, produces an output signal which indicates the oxygen storage capacity of the catalyst. Oxygen storage capacity is one method of determining the catalyst ability to convert exhaust emissions effectively. If the catalyst is functioning correctly, the post catalyst HO2S signal will be far less active than that produced by the pre-catalyst HO2S. If the PCM detects excessive post catalyst signal activity, outside of an acceptable range, for an extended period of time, the PCM will set this DTC. This indicates that the TWC oxygen storage capacity is below a threshold considered acceptable.

Conditions for Running the DTC
  1. Meet conditions for engine warm up. Use the scan tool catalyst data list in order to verify the following.
    2. • The following types of diagnostic trouble codes (DTCs) are not set:
       - Misfire
       - Fuel trim
       - Injector or ignition control circuit
       - Evaporative emission (EVAP) system
       - Heated oxygen sensor (HO2S)
       - Vehicle speed sensor (VSS)
       - Idle air control (IAC) sensor
       - Exhaust gas recirculation (EGR) system
       - Throttle position (TP) sensor
       - Intake air temperature (IAT) sensor
       - Manifold absolute pressure (MAP) sensor
       - Engine coolant temperature (ECT) sensor
       - Mass air flow (MAF) sensor
       - Crankshaft position (CKP) sensor
    • Engine has been running longer than approximately 9 minutes.
    • IAT is between -18°C and +80°C (0°F and 176°F).
    • ECT is between 75°C and 120°C (167°F and 248°F).
    • BARO is above 75 kPa.
    • Closed Loop
  2. Warm up the catalyst.
    3. • Fully open hood
    • Transmission is in park (automatic) or neutral (manual).
    • Set the parking brake.
    • Engine speed is more than 1,500 RPM for 1 minute.
    • Return to idle.
  3. Test the catalyst.
    4. • Transmission is in drive (automatic) or neutral (manual).
    • Within 5-20 seconds, HO2S 1 should toggle rich above 600 mv for up to 7 seconds, then it may toggle lean below 300 mv for up to 7 seconds.
    • Using the scan tool, check and see if DTC P0420 has passed or failed this ignition cycle

Conditions for Setting the DTC

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

Action Taken When the DTC Sets
    • The PCM illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
    • The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Freeze Frame and/or Failure Records.

Conditions for Clearing the MIL/DTC
    • The PCM turns the MIL OFF after 3 consecutive drive trips during which the diagnostic runs and passes.
    • A last test failed, or the current DTC, clears when the diagnostic runs and passes.
    • A History DTC clears after 40 consecutive warm-up cycles, if no other emission related diagnostic failures are reported.
    • Use a scan tool in order to clear the MIL diagnostic trouble code.
    • Interrupting the PCM battery voltage may or may not clear DTCs. This practice is not recommended. Refer to Powertrain Control Module Description , Clearing Diagnostic Trouble Codes.

Diagnostic Aids

Notice: Use the connector test adapter kit J 35616-A for any test that requires probing the following items:

   • The PCM harness connectors
   • The electrical center fuse/relay cavities
   • The component terminals
   • The component harness connector
Using this kit will prevent damage caused by the improper probing of connector terminals.

Check 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 100 RPM from the desired idle.
       - The throttle position (TP) is 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 the desired idle.
       - The throttle position (TP) is 0 percent.
       - The short term integrator is between -20 percent and +20 percent.
    • The catalyst test may abort due to a change in the engine load, such as A/Cor the coolant fan. Repeat the test if a load change occurs during the test.
    • More than 6 tests may have to be attempted to get 6 completed tests. An aborted test counts as an attempted test.
    • The number of attempted tests is limited to 18 per ignition cycle.
    • After returning to an idle, the HO2S 1 signal may stay rich or lean for several seconds causing the test to be delayed.
    •  Poor connections at the PCM -- Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connections.
    • Harness damage -- 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

The numbers below refer to the step numbers on the diagnostic table.

  1. 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.

    2.

  2. Clearing the DTCs allows the catalyst test to be completed up to 6 times this ignition cycle. The diagnostic will abort if the A/C clutch cycles. Turn the A/C OFF. 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.

    3.

  3. This step includes checks for conditions that can cause the three-way converter to appear degraded. Repair any problems found before proceeding with this table.

    4.

  4. If the three-way converter needs to be replaced, make sure that another condition is not present which could damage the converter. These conditions may include: misfire, high engine oil or coolant consumption, HO2S silicon contamination, retarded spark timing or weak spark. Correct any possible causes of converter damage before replacing the converter.

Step

Action

Value(s)

Yes

No

1

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

Are any other DTCs set?

--

Go to the applicable DTC table

Go to Step 3

3

  1. Clear the DTCs using the scan tool.

    2. Important: If the A/C clutch cycles, the diagnostic will abort.

  2. Turn the A/C OFF.
  3. Start the engine and idle until normal operating temperature is reached.
  4. Fully open the hood.
  5. Operate the vehicle within the conditions that are required for this diagnostic to run. Refer to the Conditions for Running the DTC.

    6. Important: If more than 6 tests have been attempted and the DTC has not passed or failed this ignition cycle the test may be aborting. Refer to Diagnostic Aids .

  6. The diagnostic test may need to be completed up to 6 times in order to pass or fail.

Does the scan tool indicate the DTC ran and passed this ignition cycle?

--

System Ok

Go to Step 4

4

  1. Visually and physically inspect the three-way catalytic converter for damage.
  2. Check for the following:
    3. • Dents, holes, or other physical damage
    • Severe discoloration caused by excessive temperatures
    • Internal rattle caused by damaged catalyst substrate
  3. Also, ensure that the three-way catalytic converter is a proper original equipment manufacturer part.

Was a problem found?

--

Go to Step 7

Go to Step 5

5
  1. Visually and physically inspect the exhaust system for leaks.
  2. If a problem is found, repair as necessary. Refer to Exhaust System Inspection in Engine Exhaust.

Was a problem found and corrected?

--

Go to Step 8

Go to Step 6

6

Visually check for the following conditions:

    • Damaged or contaminated heated oxygen sensors
    • HO2S wiring harness damage

Was a problem found and corrected?

--

Go to Step 8

Go to Step 7

7

Notice: In order to avoid damaging the replacement three-way catalytic converter, correct the engine misfire or mechanical fault before replacing the three-way catalytic converter.

Replace the three way catalytic converter. Refer to Catalytic Converter Replacement in Engine Exhaust.

Is the action complete?

--

Go to Step 8

--

8
  1. Clear the DTCs using the scan tool.

    2. Important: If the A/C clutch cycles, the diagnostic will abort.

  2. Turn the A/C OFF.
  3. Start the engine and idle until normal operating temperature is reached.
  4. Fully open the hood.
  5. Operate the vehicle within the conditions that are required for this diagnostic to run. Refer to the Conditions for Running the DTC.

    6. Important: If more than 6 tests have been attempted and the DTC has not passed or failed this ignition cycle, the test may be aborting. Refer to Diagnostic Aids.

  6. The diagnostic test may need to be completed up to 6 times in order to pass or fail.

Does the scan tool indicate the DTC ran and passed this ignition cycle?

--

Go to Step 9

Go to Step 4

9

Review Captured Info using the scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to the applicable DTC table

System OK