Mitsubishi FUEL Manual page 134

13A-134
Code No. P0421 Catalyst malfunction (Bank 1)
Range of Check
D The engine speed is 3,000 r/min or less.
D During driving
D During air/fuel ratio feedback control
Set Conditions
D The ratio between the right bank oxygen sensor (rear) and the right bank
oxygen sensor (front) output frequencies reaches 0.8 per 12 seconds on
average.
Check the exhaust manifold. (Are there any cracks?)
MUT-II Data list
59 Right bank oxygen sensor (rear)
D Transmission: 2nd
D Drive with wide open throttle
OK: 600 - 1,000 mV
MUT-II Data list
11 Right bank oxygen sensor (front)
OK: 600 - 1,000 mV when racing suddenly
MUT-II Data list
11 Right bank oxygen sensor (front)
D Transmission: 2nd
OK: Changeover between 0 - 400 mV and 600 - 1,000
mV occur 15 times in 10 seconds.
Replace the right bank oxygen sensor (rear).
Check the trouble symptoms.
Replace the right bank side catalytic converter.
Check the trouble symptoms.
Replace the engine-ECU.
MPI <6A1> -
OK
OK
OK
OK
NG
NG
Troubleshooting
Probable cause
D Malfunction of right bank side catalyst
D Malfunction of the right bank oxygen sensor (front)
D Malfunction of the right bank oxygen sensor (rear)
D Malfunction of engine-ECU
NG
Repair
NG
Check the oxygen sensor (rear) system <Bank 1 sensor 2>
(Refer to P.13A-116, INSPECTION PROCEDURE FOR
DIAGNOSIS TROUBLE CODE P0136.)
NG
Check the oxygen sensor (front) system <Bank 1 sensor 1>
(Refer to P.13A-113, INSPECTION PROCEDURE FOR
DIAGNOSIS TROUBLE CODE P0130.)
NG
Replace the right bank oxygen sensor (front).