Mitsubishi Electric Lancer Evolution-VII Workshop Manual page 473

54B-6
Code No. 21 Short circuit in communication lines.
This diagnostic code is output when the voltage on an SWS communication line
goes LOW for 0.3 seconds. The diagnosis code output stops when the
ETACS-ECU data line voltage goes HIGH for 0.3 seconds, or when the
ETACS-ECU receives a normal signal from another ECU or switch. During the
output of this code, other codes are suppressed.
Check the following connectors: C-228, C-203, C-135,
A-11X, C-102, C-24, E-07, C-110, D-25, C-25
Check the trouble symptoms.
Check the harnesses of the column switch ETACS-ECU,
front-ECU, power window main switch.
Is code 21 no longer output when column switch connector
C-203 is disconnected? (Note that code 12 is still output with
C-203 disconnected.)
When the front-ECU connector A-11X disconnected, is Code
NO. 21 output? (However, Code No. 13 is output)
When the power window main switch connector E-07 is
disconnected, is Code No. 21 output?
Replace ETACS-ECU.
SWS -
OK
NG
OK
YES
YES
YES
Troubleshooting
Probable cause
D Column switch fault
D front-ECU fault
D Power window main switch fault
D ETACS-ECU fault
D Harness or connector fault
NG
Repair
NG
Repair
NO
Replace column switch.
NO
Replace front-ECU.
NO
Replace power window main switch.