GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2003 🢒 S10 Pickup - 2WD 🢒 DTC 🢒 DTC P0420

Circuit Description

A three-way catalytic converter (TWC) is used in order to control the exhaust emissions of hydrocarbons (HC), carbon monoxide (CO) and oxides of nitrogen (NOx). The catalyst within the converter promotes a chemical reaction which oxidizes the HC and the CO that is present in the exhaust gas. This will convert the HC and the CO into a harmless water vapor and a carbon dioxide, and reduces the NOx, converting the NOx into nitrogen. The catalytic converter also has the ability to store oxygen. The powertrain control module (PCM) has the capability to monitor this process by using a heated oxygen sensor (HO2S) which is in the exhaust stream past the TWC. The HO2S produces an output signal which indicates the oxygen storage capacity of the catalyst. This in turn indicates the catalysts ability to convert the exhaust emissions effectively. The PCM monitors the catalyst efficiency by first allowing the catalyst to heat up, waiting for a stabilization period while the engine is idling. Then, the PCM adds and removes the fuel while monitoring the reaction of the HO2S. When the catalyst is functioning properly, the HO2S 2 response to the extra fuel is slow compared to the oxygen sensor (O2S) 1. When the HO2S 2 response is close to that of the O2S 1, the oxygen storage capability or efficiency of the catalyst is considered to be bad and the malfunction indicator lamp (MIL) will illuminate.

Conditions for Running the DTC
    • DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0130, P0131, P0132, P0133, P0134, P0137, P0138, P0140, P0141, P0171, P0172, P0201-P0204, P0300, P0301-P0304, P0325, P0336, P0341, P0410, P0440, P0442, P0446, P0452, P0453, P0502, P0503, P0506, P0507, P0601, P0602, P1133, P1441 are not set.
    • The engine speed is more than 1,200 RPM for a minimum of 36 seconds since the end of last idle period.
    • The barometric pressure (BARO) is more than 72 kPa.
    • The intake air temperature (IAT) between -20.5 to +60.5°C (-4.9 to +141°F).
    • The engine coolant temperature (ECT) between 75-125°C (167-257°F).
    • The battery voltage is more than 9 volts.
    • The calculated air flow is less than 11 g/sec.
    • The engine run time is more than 530 seconds.
    • The vehicle speed is less than 4.8 km/h (3 mph).
    • Tests attempted this trip are less than 12.
    • The predicted catalyst temperature is between 345-477°C (653-891°F).

Conditions for Setting the DTC

The PCM determines that the oxygen storage capacity of the TWC is degraded past a calibrated value.

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

Thoroughly check any circuitry suspected of causing the intermittent complaint . Inspect for the following conditions :

    • A poor connection
    • A rubbed through wire insulation
    • A wire that is broken inside the insulation
    • Backed out terminals
    • Improper mating
    • Broken locks
    • Physical damage to the wiring harness

Test Description

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

  1. If any component diagnostic trouble codes (DTCs) are set, diagnose those DTCs first. A malfunction in a component can cause the converter to appear degraded or may have caused the malfunction.

    2.

  2. This step includes inspecting for conditions that can cause the TWC to appear degraded. Repair any problems found before proceeding with this table.

    3.

  3. If you need to replace the TWC, make sure that another condition is not present which would cause damage to the converter. Correct any possible causes of converter damage before replacing the TWC in order to avoid damage to the replacement converter.

Step

Action

Yes

No

1

Did you perform the Diagnostic System Check-Engine Controls?

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Are any other DTCs set?

Go to Diagnostic Trouble Code (DTC) List

Go to Step 3

3

  1. Verify that the three-way catalytic converter (TWC) is an original equipment part.
  2. Inspect the TWC for damage such as dents, severe discoloration caused by excessive temperature, holes, etc.
  3. Ensure that the internal TWC rattle caused by damaged catalyst is not present.
  4. Inspect the exhaust system for the following conditions:
    5. • Any leaks
    • Any damage
    • Any loose or missing hardware
    • Refer to Exhaust Leakage in Engine Exhaust.
  5. Ensure that the O2S 1 and the HO2S 2 are secure and that the pigtails and wiring are not damaged or contacting the exhaust.

Did you find and correct the condition?

Go to Step 5

Go to Step 4

4

Important: Before replacing a TWC, correct any condition that may have damaged the TWC.

Replace the TWC. Refer to Catalytic Converter Replacement in Engine Exhaust.

Did you complete the replacement?

Go to Step 5

--

5
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

Go to Step 2

Go to Step 6

6

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

Go to Diagnostic Trouble Code (DTC) List

System OK