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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 1068 (Engine Controls Diagnosis - 4.8L, 5.3L, & 6.0L (DTCS P0141 To P0446)) >> Diagnosis >> DTC P0420 or P0430 (With HP2) >> Test Description

Test Description

WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

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

  1. 5:  A catalytic converter which has been discolored may be due to an engine running rich, lean or had a previous misfire. Verifying the fuel trim percentages may be of assistance in determining if such a condition exists.
  2. 6:  This steps inspects for conditions than can cause the TWC efficiency to appear degraded.
DTC P0420 or P0430 (With HP2)

Step Action Values Yes No
1 Did you perform the Diagnostic System Check - Vehicle? - Go to Step 2  Go to Diagnostic System Check - Engine Controls
2 Review the DTC information on the scan tool.
Are any other DTCs set?		 - Go to Diagnostic Trouble Code (DTC) List Go to Step 3 
3
  1. Start and idle the engine.
  2. Allow the engine to reach operating temperature.
  3. Increase the engine speed to 2,000 RPM for 2 minutes.
  4. Ensure Closed Loop operation is enabled.
  5. Return the engine to a stabilized idle.
  6. Observe the HO2S 2 voltage parameter on the scan tool for the applicable bank.
Is the applicable HO2S 2 voltage parameter transitioning below the first specified value and above the second specified value?		 350 mV
600 mV		 Go to Step 5  Go to Step 4 
4
  1. Clear the DTCs with a scan tool.
  2. Start the engine.
  3. 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 DTC P0420 or P0430 set?		 - Go to Step 5  Go to Diagnostic Aids
5 
IMPORTANT: Verify that the three-way catalytic converter (TWC) is a high quality part that meets the OEM specifications.
Visually and physically inspect the TWC for the following conditions:
  • Physical damage
  • Severe discoloration caused by excessive temperatures
  • Internal rattles caused by loose catalyst substrate
  • Restrictions-Refer to Restricted Exhaust .
Did you find and correct the condition?		 - Go to Step 10  Go to Step 6 
6  Visually inspect the exhaust system for the following conditions:
  • Leaks-Refer to Exhaust Leakage .
  • Physical damage
  • Loose or missing hardware
  • The heated oxygen sensor (HO2S) 2 for the applicable bank for proper torque

Did you find and correct the condition?		 - Go to Step 10  Go to Step 7 
7 Visually inspect the HO2S 2 at the applicable bank for the following conditions:
  • The pigtail and wiring harness contacting the exhaust or any ground
  • Road damage

Did you find a condition?		 - Go to Step 8  Go to Step 9 
8 Replace the applicable HO2S 2 sensor. Refer to Heated Oxygen Sensor (HO2S) Replacement Bank 1 Sensor 2 or Heated Oxygen Sensor (HO2S) Replacement Bank 2 Sensor 2 .
Did you complete the replacement?		 - Go to Step 10  -
9
NOTE: 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 TWC. Refer to Catalytic Converter Replacement (4.3L, 4.8L, and 5.3L Engines) or Catalytic Converter Replacement (6.0L and 8.1L Engines) or Catalytic Converter Replacement (6.6L Engine) .Did you complete the replacement?		 - Go to Step 10  -
10
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
    4. CAUTION: Refer to Road Test Caution in Cautions and Notices.
    IMPORTANT: A new catalyst may fail this test due to out-gassing of the internal matting. If this occurs, operate the vehicle at highway speeds for approximately 1 hour and retest the vehicle.
  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 11 
11 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
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