DTC Advanced Diagnostics: P0420
DTC P0420:Catalyst System Efficiency Below Threshold

General Description

The three way catalytic converter (TWC) converts hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx) in the exhaust gas to water vapor, carbon dioxide (CO2), and dinitrogen (N2). The powertrain control module (PCM) fluctuates the air/fuel ratio temporarily to detect the performance of the TWC and measures the degree of fluctuation in the secondary heated oxygen sensor (secondary HO2S (sensor 2)) output. If the accumulated value for a set time is too great, deterioration of the performance of the catalyst is detected, the PCM detects a malfunction and stores a DTC.

Monitor Execution, Sequence, Duration, DTC Type
Execution
Once per driving cycle
Sequence
None
Duration
7.5 seconds or more
DTC Type
Two drive cycles, MIL on

Enable Conditions
Condition
Minimum
Maximum
Elapsed time that secondary HO2S activity is not monitored after starting the engine
15 seconds
–
Engine coolant temperature
[ECT SENSOR 1]
156 °F (69 °C)
–
Intake air temperature
[IAT sensor (1)]
-13 °F (-25 °C)
–
Estimated TWC temperature*1
1,022 °F (550 °C)
–
Estimated TWC temperature*2
986 °F (530 °C)
–
Vehicle speed [VEHICLE SPEED]
26 mph (41 km/h)
–
Fuel trim
0.75
1.47
Fuel feedback
Closed loop at stoichiometric
Monitoring priority
P0133, P219C, P219D, P219E, P219F
Other
Has record of deceleration at least once
Cruise load or more
*1: L15B7 (except Si), L15BY
*2: Si, L15BA
[ ]: HDS Parameter

Malfunction Threshold
The secondary HO2S (sensor 2) fluctuation integration value is 3.0 V or more for at least 7.5 seconds.

Possible Cause
NOTE: The causes shown may not be a complete list of all potential problems, and it is possible that there may be other causes.
TWC purification performance deterioration
Secondary HO2S (sensor 2) line electrical noise overlapped
Secondary HO2S (sensor 2) connector loose connection
Exhaust system change (non-genuine part)

Confirmation Procedure
Operating Condition

1.
Start the engine. Hold the engine speed [ENGINE SPEED] at 3,000 rpm without load (CVT in P or N, M/T in neutral) until the radiator fan comes on.
2.
Drive the vehicle at a speed between 45 - 75 mph (73 - 120 km/h) for at least 5 minutes, to warm up the TWC.
3.
Drive at a steady speed between 55 - 75 mph (89 - 120 km/h) for at least 10 seconds.
4.
Decelerate with the throttle valve fully closed.
5.
Repeat Driving Pattern steps 3 through 4, four times.
6.
Drive at steady speed 25 mph (40 km/h) or more for at least 68 seconds.
After disconnecting the 12 volt battery, extend Driving Pattern step 6 to 4 minutes or longer.
Drive the vehicle in this manner only if the traffic regulations and ambient conditions allow.

Diagnosis Details
Conditions for setting the DTC
When a malfunction is detected during the first drive cycle, a Pending DTC is stored in the PCM memory. If the malfunction returns in the next (second) drive cycle, the MIL comes on and a Confirmed DTC and the freeze data are stored.

Conditions for clearing the DTC
The MIL is cleared if the malfunction does not return in three consecutive trips in which the diagnostic runs. The MIL, the Pending DTC, the Confirmed DTC, and the freeze data can be cleared with the scan tool Clear command or by disconnecting the 12 volt battery.