Mitsubishi Lancer Evolution-IV Workshop Manual page 355

CHASSIS ELECTRICAL –
Code No. 21 Communication system between MUT-II and
engine-ECU
After the ignition switch is turned to the ON position, the confirmation code is not
received from the engine-ECU within the allowable time, or an abnormal code is received.
Is diagnosis code No. 54 being gener-
ated by the engine-ECU?
YES
Check the following connectors.
B-100, B-65, B-61
OK
Check trouble symptoms.
Code No. 31 EEPROM abnormality inside immobilizer-
ECU
No data has been written to the EEPROM inside the immobilizer-ECU.
Check trouble symptoms.
Ignition Switch and Immobilizer System
NO
Check the engine-ECU power source
and the earth circuit.
(Refer to GROUP 13A – Troubleshoot-
ing.)
NG
Repair
NG
Check the harness wire between
engine-ECU and immobilizer-ECU.
Check trouble symptoms.
Replace the immobilizer-ECU.
Check trouble symptoms.
NG
Replace the immobilizer-ECU.
Probable cause
D Malfunction of harness or connector
D Malfunction of the engine-ECU
D Malfunction of the immobilizer-ECU
NG
OK
NG
NG
Probable cause
D Malfunction of the immobilizer-ECU
54-15
Repair
Replace the engine-ECU.