Mitsubishi Evolution X. Manual - part 546

DIAGNOSIS

TSB Revision

KEYLESS OPERATION SYSTEM (KOS)

42B-91

.

TROUBLESHOOTING HINTS

• Malfunction of the inside transmitter antenna 

assembly (front)

• Malfunction of the KOS-ECU

• Damaged wiring harness and connectors

DIAGNOSIS

STEP 1. Check KOS-ECU connector C-05 and inside 
transmitter antenna assembly (front) connector C-121 for 
loose, corroded or damaged terminals, or terminals 
pushed back in the connector.
Q: Are KOS-ECU connector C-05 and inside transmitter 

antenna assembly (front) connector C-121 in good 
condition?
YES : Go to Step 2.
NO :  Repair or replace the damaged component(s). Refer 

to GROUP 00E, Harness Connector Inspection 

P.00E-2

. Check that the inside transmitter antenna 

assembly (front) works normally.

STEP 2. Check the wiring harness between the KOS-ECU 
connector C-05 (terminal Nos. 6, 16, 40) and inside 
transmitter antenna assembly (front) connector C-121 
(terminal Nos. 3, 2, 1) for open circuit.
(1) Disconnect KOS-ECU connector C-05 and inside 

transmitter antenna assembly (front) connector C-121, and 
check the wiring harness.

(2) Check the wiring harness between KOS-ECU connector 

C-05 (terminal No.6) and inside transmitter antenna 
assembly (front) connector C-121 (terminal No.3).

OK: Continuity exists (2 

Ω or less)

(3) Check the wiring harness between KOS-ECU connector 

C-05 (terminal No.16) and inside transmitter antenna 
assembly (front) connector C-121 (terminal No.2).

OK: Continuity exists (2 

Ω or less)

AC709707FN

Harness side: C-05

Harness side: C-121

AC709707 FO

Harness side: C-05

Harness side: C-121

DIAGNOSIS

TSB Revision

KEYLESS OPERATION SYSTEM (KOS)

42B-92

(4) Check the wiring harness between KOS-ECU connector 

C-05 (terminal No.40) and inside transmitter antenna 
assembly (front) connector C-121 (terminal No.1).

OK: Continuity exists (2 

Ω or less)

Q: Is the wiring harness between KOS-ECU connector C-05 

(terminal Nos. 6, 16, 40) and inside transmitter antenna 
assembly (front) connector C-121 (terminal Nos. 3, 2, 1) 
in good condition?
YES  : Go to Step 3.
NO (KOS-ECU connector C-05 terminal No.6 

− inside 

transmitter antenna assembly (front) connector C-121 
terminal No.3.) : Repair the wiring harness between 

KOS-ECU connector C-05 (terminal No.6) and inside 
transmitter antenna assembly (front) connector C-121 
(terminal No.3).

NO (KOS-ECU connector C-05 terminal No.16 

− inside 

transmitter antenna assembly (front) connector C-121 
terminal No.2.) : Repair the wiring harness between 

KOS-ECU connector C-05 (terminal No.16) and 
inside transmitter antenna assembly (front) connector 
C-121 (terminal No.2).

NO (KOS-ECU connector C-05 terminal No.40 

− inside 

transmitter antenna assembly (front) connector C-121 
terminal No.1.) : Repair the wiring harness between 

KOS-ECU connector C-05 (terminal No.40) and 
inside transmitter antenna assembly (front) connector 
C-121 (terminal No.1).

AC709707

Harness side: C-121

Harness side: C-05

FP

DIAGNOSIS

TSB Revision

KEYLESS OPERATION SYSTEM (KOS)

42B-93

STEP 3. Check the wiring harness between the inside 
transmitter antenna assembly (front) connector C-121 
(terminal Nos. 3, 2, 1) and the ground for short circuit.
(1) Disconnect inside transmitter antenna assembly (front) 

connector C-121, and check the wiring harness.

(2) Check the wiring harness between inside transmitter 

antenna assembly (front) connector C-121 (terminal No.3) 
and ground

OK: No continuity

(3) Check the wiring harness between inside transmitter 

antenna assembly (front) connector C-121 (terminal No.2) 
and ground

OK: No continuity

(4) Check the wiring harness between inside transmitter 

antenna assembly (front) connector C-121 (terminal No.1) 
and ground

OK: No continuity

Q: Is the wiring harness between inside transmitter 

antenna assembly (front) connector C-121 (terminal 
Nos. 3, 2, 1) and the ground in good condition?
YES  : Go to Step 4.
NO [inside transmitter antenna assembly (front) 
connector C-121 terminal No.3 

− ground.] : Repair the 

wiring harness between inside transmitter antenna 
assembly (front) connector C-121 (terminal No.3) and 
ground.

NO [inside transmitter antenna assembly (front) 
connector C-121 terminal No.2 

− ground.] : Repair the 

wiring harness between inside transmitter antenna 
assembly (front) connector C-121 (terminal No.2) and 
the ground.

NO [inside transmitter antenna assembly (front) 
connector C-121 terminal No.1 

− ground.] : Repair the 

wiring harness between inside transmitter antenna 
assembly (front) connector C-121 (terminal No.1) and 
the ground.

AC709707IL

Harness side: C-121

AC709707IM

Harness side: C-121

AC709707IN

Harness side: C-121

DIAGNOSIS

TSB Revision

KEYLESS OPERATION SYSTEM (KOS)

42B-94

STEP 4. Keyless operation system communication test
Check that the communication with the interior transmitter 
antenna assembly (front) is normal (Refer to Antenna Test 

P.42B-275

).

Antennas to be checked

• front antenna (interior)

OK: Normal is displayed.

Q: Is the check result normal?

YES : Go to Step 5.
NO :  Replace the interior transmitter antenna assembly 

(front).

STEP 5. Check whether the diagnostic trouble code is 
reset.
(1) Erase the DTC.
(2) Turn the ignition switch from the LOCK (OFF) position to the 

ON position.

(3) Check if the DTC is set.
Q: Is the DTC set?

YES : Replace KOS-ECU and register the ID codes (Refer 

to 

P.42B-12

).

NO :  The procedure is complete.