Mitsubishi 1992 3000GT, Service Manual

Page: 148 / 1308

MULTIPORT FUEL INJECTION Troubleshooting
DTC No. Title
PO400 Exhaust Gas Recirculation Flow Malfunction
Probable causes
I
Background EGR valve does not open.
l
When the EGR solenoid switches from OFF to ON while the engine is running, EGR gas
l
EGR control vacuum is too low.
flows.
l
The engine control module checks how the EGR gas flow signal changes.
Range of Check, Set Conditions
The EGR gas flow signal changes little when the EGR solenoid switches from OFF to ON.
l
EGR solenoid failed.
l
Open or shorted EGR solenoid
circuit, or loose connector.
l
Manifold differential pressure
sensor failed.
Engine control module failed.
DTC No.
Title
PO403 Exhaust Gas Recirculation Solenoid Malfunction
Probable causes
Background
l
EGR solenoid failed.
l
The engine control module checks current flows in the EGR solenoid drive circuit when
l
Open or shorted EGR solenoid
the solenoid is ON and OFF.
Range of Check, Set Conditions
No surge voltage is detected even when the EGR solenoid is turned off.
circuit, or loose connector.
Engine control module failed.
DTC No.
Title
PO421
Probable causes
Warm Up Catalyst Efficiency Below Threshold (Bank 1)
Background
Catalytic converter deteriorated.
l
The signal from the heated oxygen sensor which follows the catalytic converter differs
l
Engine control module failed.
from that which precedes the catalytic converter. That is because the catalytic converter
purifies exhaust gas. When the catalytic converter has deteriorated, the signal from the
heated oxygen sensor which follows the catalytic converter becomes similar to that which
precedes the catalytic converter.
l
The engine control module checks the outputs of the heated oxygen sensor signals.
Range of Check, Set Conditions
The relation between the signals from the heated oxygen sensors preceding (engine side) and
following the catalytic converter meets specified condition.
Probable causes
I
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