Honda Civic Service Manual page 374

Catalytic Converter System
DTC Troubleshooting
DTC P0420: Catalytic System Efficiency
Below Threshold
NOTE: lf some of the DTCS listed below are stored at
the same time as DTC P0420, troubleshoot those DTCS
first, then recheck for DTC P0420.
P 0 1 3 7 , P 0 1 3 8 : S e c o n d a r y H e a t e d O x y g e n S e n s o r
(secondary HO2S) (Sensor 2)
P 0 1 4 1 : S e c o n d a r y H O 2 S ( S e n s o r 2 ) h e a t e r
1 . R e s e t t h e E C M { s e e p a g e 1 ' l - 4 } , t h e n c o n t i n u e t o
step 2 through 5 to reset the readiness code.
2. Start the engine. Hold the engine at 3,000 rpm with
n o l o a d ( i n n e u t r a l ) u n t i l t h e r a d i a t o r f a n c o m e s o n .
D r i v e f o r a b o u t l 0 m i n u t e s w i t h o u t s t o p p i n g . Y o u r
speeo can vary.
With the transmission in 4th gear, drive at a steady
speed between 50 62 mph (80-'100 km/h) for
30 seconds.
Repeat step 4 three times. Between each repetition,
close the throttle completely for 1 2 seconds. lf
the engine is stopped during this part of the
procedure, repeat steps 3, 4 and 5.
Check for a Temporary DTC with the scan tool.
Does the scan tool indicate Temporaty DTC
P0420?
YES Check the TWC. lf necessary, replace the
TWC.I
N O C h e c k f o r r e a d i n e s s c o d e c o m p l e t i o n . l f t h e
readiness is complete, it was a interminent failure,
and the system is OK at this time. lf the readiness
code is incomplete, repeat steps 2 through 5.1
4 .
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