Mitsubishi FUEL Manual page 135

Code No. P0431 Catalyst malfunction
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 left bank oxygen sensor (rear) and the left 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
69 Left bank oxygen sensor (rear)
D Transmission: 2nd
D Drive with wide open throttle
OK: 600 - 1,000 mV
MUT-II Data list
39 Left bank oxygen sensor (front)
OK: 600 - 1,000 mV when racing suddenly
MUT-II Data list
39 Left 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 left bank oxygen sensor (rear).
Check the trouble symptoms.
Replace the left 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 left bank side catalyst
D Malfunction of the left bank oxygen sensor (front)
D Malfunction of the left bank oxygen sensor (rear)
D Malfunction of engine-ECU
NG
Repair
NG
Check the oxygen sensor (rear) system <Bank 2 sensor 2>
(Refer to P.13A-31, INSPECTION PROCEDURE FOR
DIAGNOSIS TROUBLE CODE P0136.)
NG
Check the oxygen sensor (front) system <Bank 2 sensor 1>
(Refer to P.13A-113, INSPECTION PROCEDURE FOR
DIAGNOSIS TROUBLE CODE P0130.)
NG
Replace the left bank oxygen sensor (front).
13A-135