DTC Troubleshooting: P0420
DTC P0420: Catalyst System Efficiency Below Threshold
NOTE:
Before you troubleshoot, review the general troubleshooting information.
If some of the DTCs listed below are stored at the same time as DTC P0420, troubleshoot them first, then recheck for DTC P0420.
P0137, P0138, P2270: Secondary HO2S (Sensor 2)
P0141: Secondary HO2S (Sensor 2) heater
P0300: Random misfire
P0301, P0302, P0303, P0304: No. 1?No. 4 cylinder misfire
Poor quality fuel may cause this DTC.

DTC Description
Confirmed DTC
Pending DTC
Freeze Frame
P0420 Catalyst System Efficiency Below Threshold
      

1.
PGM-FI system check 1:

PGM-FI system check 1
?1.
Turn the vehicle to the ON mode.

?2.
Clear the DTC with the HDS.


?3.
Start the engine.

?4.
Hold the engine speed at 3,000 rpm without load (in P or N) until the radiator fan comes on, then let it idle.

?5.
Test-drive under these conditions:
Engine coolant temperature (ECT SENSOR 1) above 158 °F (70 °C)
Transmission in D
Vehicle speed between 45?75 mph (70?120 km/h) for 5 minutes or more with cruise control set
Vehicle speed between 55?75 mph (90?120 km/h) for 10 seconds, then decelerate (with the throttle fully closed). Repeat this three or more times
Maintain the vehicle speed at 55 mph (90 km/h) for 4 minutes or more with cruise control set.

Signal
Current conditions
Values
Unit
ECT SENSOR 1
    
VEHICLE SPEED
    

?6.
Monitor the OBD STATUS for DTC P0420 in the DTCs MENU with the HDS.
DTC Description
OBD STATUS
P0420 Catalyst System Efficiency Below Threshold
  

Does the HDS indicate FAILED?

     
YES
     
     
     
     
NO
     
     
     
If the HDS indicates EXECUTING, go to step 2. If the HDS indicates OUT OF CONDITION, meet the test conditions and recheck. If the HDS indicates PASSED, intermittent failure the system is OK at this time.
2.
PGM-FI system check 2:

PGM-FI system check 2
?1.
Continue test-drive until a result comes on.

?2.
Monitor the OBD STATUS for DTC P0420 in the DTCs MENU with the HDS.
DTC Description
OBD STATUS
P0420 Catalyst System Efficiency Below Threshold
  

Does the HDS indicate FAILED?

     
YES
     
     
     
     
NO
     
     
     
If the HDS indicates PASSED, intermittent failure, the system is OK at this time. If the freeze data/on-board snapshot of this DTC is recorded, try to reproduce the failure under the same conditions with the freeze data/on-board snapshot. If the HDS indicates EXECUTING, keep driving until a result comes on. If the HDS indicates OUT OF CONDITION, meet the test conditions and recheck.?