DTC B240D: Front antenna(indoor) open: Diagnosis

WARNING: This page is about a different car, the 2008 Mitsubishi Lancer. However, it is still accessible from the selected car via links, so may be relevant.

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 HARNESS CONNECTOR INSPECTION . 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)
  
  Fig 1: Checking Continuity Between Connector Terminal 3 And 6
  Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
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)
  
  Fig 2: Checking Continuity Between Connector Terminal 2 And 16
  Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
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)
  
  Fig 3: Checking Continuity Between Connector Terminal 1 And 40
  Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
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).
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
  
  Fig 4: Checking Continuity Between Inside Transmitter Antenna Assembly (Front) Terminal 3 And Ground
  Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
3. Check the wiring harness between inside transmitter antenna assembly (front) connector C-121 (terminal No.2) and ground
  OK: No continuity
  
  Fig 5: Checking Continuity Between Inside Transmitter Antenna Assembly (Front) Terminal 2 And Ground
  Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
4. Check the wiring harness between inside transmitter antenna assembly (front) connector C-121 (terminal No.1) and ground
  OK: No continuity
  
  Fig 6: Checking Continuity Between Inside Transmitter Antenna Assembly (Front) Terminal 1 And Ground
  Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
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.
STEP 4. Keyless operation system communication test
Check that the communication with the interior transmitter antenna assembly (front) is normal (Refer to ANTENNA TEST ).

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 ID CODE REGISTRATION NECESSITY JUDGMENT TABLE ).

NO : The procedure is complete.