INSPECTION PROCEDURE O-5: The fog light switch signal is not sent to the ETACS-ECU.: Diagnosis

Required Special Tools: 

• MB991223: Test Harness Set
• MB991502: Scan Tool (MUT-II)
• MB991529: Diagnostic Trouble Code Check Harness

1. STEP 1. Check the fog light switch. 
   TESTER CONNECTION SPECIFIED CONDITION CHART
   
   

   SWITCH POSITION	TESTER CONNECTION	SPECIFIED CONDITION
   Released	6 - 7	Open circuit
   Pressed	6 - 7	Less than 2 ohms

   Q: Is the fog light switch in good condition? 

   YES  : Go to Step 2.

   NO:  The wiring harness may be damaged or the connector(s) may have loose, corroded or damaged terminals, or terminals pushed back in the connector. Repair the wiring harness as necessary. The fog light switch input signal should be able to be checked and the fog lights should work normally.

   Fig 1: Identifying Connector C-139 - Harness Side

   Courtesy of DAIMLERCHRYSLER CORPORATION
   Fig 2: Identifying Fog Light Switch

   Courtesy of DAIMLERCHRYSLER CORPORATION
2. STEP 2. Check the ground circuit to the fog light switch. Test at fog light switch connector C-139. 
   1. Disconnect the fog light switch connector C-139 and measure the resistance available at the wiring harness side of the connector.
      Fig 3: Identifying Connector C-139 - Harness Side

      Courtesy of DAIMLERCHRYSLER CORPORATION
   2. Measure the resistance between terminal 7 and ground.
      • The resistance should equal 2 ohms or less.

   Q: Is the measured resistance 2 ohms or less? 

   YES  : Go to  Step 5.

   NO:  Go to Step 3.

   Fig 4: Identifying Connector C-139 - Harness Side

   Courtesy of DAIMLERCHRYSLER CORPORATION
3. STEP 3. Check the fog light switch connector C-139 for loose, corroded or damaged terminals, or terminals pushed back in the connector. 

   Q: Is fog light switch connector C-139 in good condition? 

   YES  : Go to Step 4.

   NO:  Repair or replace the damaged component(s). Refer to , HARNESS CONNECTOR INSPECTION . The fog light switch input signal should be able to be checked and the fog light should work normally.

   Fig 5: Identifying Connector C-139 - Harness Side

   Courtesy of DAIMLERCHRYSLER CORPORATION
4. STEP 4. Check the wiring harness between fog light switch connector C-139 (terminal 7) and ground. 
   Fig 6: Identifying Connectors C-139, C-141 - Harness Side

   Courtesy of DAIMLERCHRYSLER CORPORATION
   NOTE: Also check joint connector C-141 for loose, corroded, or damaged terminals, or terminals pushed back in the connector. If joint connector C-141 is damaged, repair or replace the damaged component(s) Refer to , HARNESS CONNECTOR INSPECTION .

   Q: Are the wiring harness between fog light switch connector C-139 (terminal 7) and ground in good condition? 

   YES  : No action is necessary and testing is complete.

   NO:  The wiring harness may be damaged or the connector(s) may have loose, corroded or damaged terminals, or terminals pushed back in the connector. Repair the wiring harness as necessary. The fog light switch input signal should be able to be checked and the fog lights should work normally.

5. STEP 5. Check the fog light switch connector C-139 and ETACS-ECU connector C-318 for loose, corroded or damaged terminals, or terminals pushed back in the connector. 

   Q: Are fog light switch connector C-139 and ETACS-ECU connector C-318 in good condition? 

   YES  : Go to Step 6.

   NO:  Repair or replace the damaged component(s). Refer to , HARNESS CONNECTOR INSPECTION . The fog light switch input signal should be able to be checked and the fog lights should work normally.

   Fig 7: Identifying Connector C-139 - Harness Side

   Courtesy of DAIMLERCHRYSLER CORPORATION
   Fig 8: Identifying Connector C-318

   Courtesy of DAIMLERCHRYSLER CORPORATION
6. STEP 6. Check the wiring harness between fog light switch connector C-139 (terminal 6) and ETACS-ECU connector C-318 (terminal 54). 

   Q: Is the wiring harness between fog light switch connector C-139 (terminal 6) and ETACS-ECU connector C-318 (terminal 54) in good condition? 

   YES  : Replace the ETACS-ECU. The fog light switch input signal should be able to be checked and the fog lights should work normally.

   NO:  The wiring harness may be damaged or the connector(s) may have loose, corroded or damaged terminals, or terminals pushed back in the connector. Repair the wiring harness as necessary. The fog light switch input signal should be able to be checked and the fog lights should work normally.

   Fig 9: Identifying Connector C-139 - Harness Side

   Courtesy of DAIMLERCHRYSLER CORPORATION
   Fig 10: Identifying Connector C-318 - Harness Side

   Courtesy of DAIMLERCHRYSLER CORPORATION