Diagnostic Trouble Code (Dtc) P0420 Catalyst System Efficiency Below Threshold - Isuzu 1999 RODEO Workshop Manual

6E1–248 RODEO X22SE 2.2L ENGINE DRIVEABILITY AND EMISSION
DIAGNOSTIC TROUBLE CODE (DTC) P0420 CATALYST SYSTEM EFFICIENCY
Circuit Description
The PCM uses the Bank 1 HO2S 1 and the Bank 1 HO2S
2 heated oxygen sensors. The Bank 1 HO2S 1 sensor
produces an output signal which indicates the amount of
oxygen present in the exhaust gas entering the
three–way catalytic converter. The Bank 1 HO2S 2
sensor produces an output signal which indicates the
oxygen storage capacity of the catalyst; this in turn
indicates the catalyst's ability to convert exhaust gases
efficiently. If the catalyst is operating efficiently, the Bank
1 HO2S 1 signal will be far more active than that produced
by the Bank 1 HO2S 2 sensor. If the PCM detects a level
of Bank 1 HO2S 2 activity that indicates the catalyst is no
longer operating efficiently, Diagnostic Trouble Code
P0420 will be set. DTC P0420 is a type A code.
Conditions for Setting the DTC
f No related Diagnostic Trouble Codes.
f The engine is operating in "Closed Loop".
f Engine air load is below 99.6%.
f Engine coolant temperature is above 60°C (140°F).
f Calculated air flow is between 10 g/second and 32
g/second.
f Change in engine load is below 3.91%.
f Engine speed is below 3500 RPM.
f Vehicle speed is between 24 km/h and 123 km/h (15
mph and 75 mph).
f Catalyst temperature is above 399°C (750°F).
BELOW THRESHOLD
f The PCM determines that the catalyst's oxygen
storage capacity is below the acceptable threshold.
Action Taken When the DTC Sets
f The PCM will illuminate the malfunction indicator lamp
(MIL) the first time the fault is detected.
f The PCM will store conditions which were present
when the Diagnostic Trouble Code was set as Freeze
Frame and in the Failure Records data.
Conditions for Clearing the MIL/DTC
f The PCM will turn the MIL OFF on the third consecutive
trip cycle during which the diagnostic has been run and
the fault condition is no longer present.
f A history Diagnostic Trouble Code P0420 will clear
after 40 consecutive warm–up cycles have occurred
without a fault.
f Diagnostic Trouble Code P0420 can be cleared by
using the Scan Tool's "Clear Info" function.
Diagnostic Aids
Check for the following conditions:
f Poor connection at PCM – Inspect harness connectors
for backed–out terminals, improper mating, broken
locks, improperly formed or damaged terminals, and
poor terminal–to–wire connection.
f Damaged harness – Inspect the wiring harness for
damage; shorts to ground, shorts to battery positive
and open circuits. If the harness appears to be OK,
observe the display on the Tech 2 while moving
D06RX048