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Three Way Catalytic Converter (TWC)
lT042O I Th" """n tool indicates Diagnostic Trouble Code (DTC) P0420: catatyst system efficiency below threshold.
Descriotion
This system evaluates the catalyst's capacity by means of the HO2S (Primary and Secondary) output during stable driving
conditions. lf deterioration has been detected during three consecutive driving cycles, the MIL comes on and DTC p0420 will
be stored.
NOTE: lf some of the DTCS listed below are stored at the same time as DTC PO42O. troubleshoot those DTCS tirst. then
troubleshoot DTC P0420.
P0136, P0139: Secondarv HO2S
P0141:
Secondary HO2S Heater
Possible Cause
. TWC Deterioration
.
Exhaust system leakage
Troubleshooting Flowchart
Problem verification:
1. Do the ECM Reset Procedure.
2 . S t a r t t h e e n g i n e . H o l d t h e
engine at 3,000 rpm with no
load (in Park or neutral) until
the radiator fan comes on,
3. Connect the SCS service con,
4. Test drive 40 - 55 mph (64 -
88 km/h) for approx. two min-
u t e s , T h e n d e c e l e r a t e I o r a t
least 3 seconds with the throt
t l e c o m p l e t e l y c l o s e d . T h e n
r e d u c e t h e v e h i c l e s p e e d t o
35 mph (56 km/h), and try to
h o l d i t u n t i l t h e r e a d i n e s s
code comes on.
I
-
The MIL has been report€d on.
-
OTC P0420 is stored.
Intermittent tailure, sFtem is OK
at this time.
ls DTC P0420 indicated?
Check the TWC {s6e 3ection 91.
lf necessary, reolace the TWC.
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Troubleshooting
