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DTC P1769: Stoplight Switch System: Diagnosis

WARNING: This page is about a different variant/trim than selected.

Required Special Tools: 

  1. STEP 1. Check the brake pedal height. 

    Refer to BRAKE PEDAL CHECK AND ADJUSTMENT .

    Q: Is the height adjusted properly? 

    1. YES:  Go to Step 2.
    2. NO:  Adjust the brake pedal to the proper height.
  2. STEP 2. Check the stoplight valve. 

    Refer to REAR COMBINATION LIGHT .

    Q: Is the stoplight valve in good condition? 

    1. YES:  Go to Step 3.
    2. NO:  Replace the stoplight switch. Refer to BRAKE PEDAL .
  3. STEP 3. Using scan tool MB991958, check data list item 19: Stoplight Switch. 
    CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.
    1. Connect scan tool MB991958 to the data link connector.
    2. Turn the ignition switch to the "ON" position.
    3. Set scan tool MB991958 to the data reading mode.
      • Item 19: Stoplight Switch.
        • When the brake pedal is depressed, the display on scan tool MB991958 should be "ON."
        • When the brake pedal is not depressed, the display on scan tool MB991958 should be "OFF."
    4. Turn the ignition switch to the "LOCK" (OFF) position.

      Q: Is the switch operating properly? 

      1. YES:  It can be assumed that this malfunction may be intermittent. Refer to HOW TO COPE WITH INTERMITTENT MALFUNCTION .
      2. NO:  Go to Step 4.
        Fig 1: Connecting Special Tool MB991910 To Data Link Connector
        G04230562Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
  4. STEP 4. Measure the stoplight switch power supply voltage at connector C-103 by backprobing. 
    1. Remove the stoplight switch from the mounting bracket.
    2. Do not disconnect connector C-103.
      Fig 2: Locating Stoplight Switch Connector C-103
      G06685115Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
    3. Measure the voltage between terminal 2 and ground by backprobing.
      • The voltage should measure battery positive voltage.

      Q: Is the measured voltage battery positive voltage? 

      1. YES:  Go to Step  7.
      2. NO:  Go to step 5.
        Fig 3: Measuring Voltage Between Terminal 2 And Ground
        G06685116Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
  5. STEP 5. Check stoplight switch connector C-103 for loose, corroded or damaged terminals, or terminals pushed back in the connector. 

    Q: Are the connector and terminals in good condition? 

    1. YES:  Go to Step 6.
    2. NO:  Repair or replace the damaged components. Refer to HARNESS CONNECTOR INSPECTION .
      Fig 4: Locating Stoplight Switch Connector C-103
      G06685115Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
  6. STEP 6. Check the harness for damage between stoplight switch connector C-103 terminal 2 and the power supply fuse. 

    Q: Is the harness wire in good condition? 

    1. YES:  Go to Step 7.
    2. NO:  Repair or replace the harness wire.
      Fig 5: Locating Stoplight Switch Connector C-103
      G06685115Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
  7. STEP 7. Measure the stoplight switch output voltage to the PCM at connector C-103 by backprobing. 
    1. Remove the stoplight switch from the mounting bracket.
    2. Do not disconnect connector C-103.
      Fig 6: Locating PCM Connector C-103
      G06685115Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
    3. Measure the voltage between terminal 1 and ground by backprobing.
      • When the switch button is out (closed circuit), voltage should equal battery positive voltage.
      • When the switch button is depressed (open circuit), voltage should measure less than 1.0 volt.
        Fig 7: Measuring Voltage Between Terminal 1 And Ground
        G06685120Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.

      Q: Is the measured voltage battery positive voltage with the switch button released (closed circuit), and less than 1.0 volt with the switch button depressed (open circuit)? 

      1. YES:  Go to Step  9.
      2. NO:  Go to Step 8.
  8. STEP 8. Check the stoplight switch. 

    Refer to STOPLIGHT SWITCH CHECK .

    Q: Does the stoplight switch pass the checks? 

    1. YES:  Go to Step 9.
    2. NO:  Replace the stoplight switch. Refer to BRAKE PEDAL .
      Fig 8: Stoplight Switch
      G05102189Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
  9. STEP 9. Measure the stoplight switch output voltage at the PCM connector B-18 by using check harness special tool MB991923. 
    1. Install the stoplight switch into the mounting bracket if it was removed.
    2. Disconnect all the connectors from the PCM.
      Fig 9: Locating PCM Connector B-18
      G06685122Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
    3. Connect special tool MB991923 (check harness) between the PCM and the body-side harness connector.
      Fig 10: Connecting Special Tool MB991923 (Check Harness) Between PCM And Body-Side Harness Connector
      G06685123Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
    4. Measure the voltage between terminal 9 and ground.
      • When the brake pedal is depressed, voltage should measure battery positive voltage.
      • When the brake pedal is not depressed, voltage should measure less than 1.0 volt.
        Fig 11: Measuring Voltage Between Terminal 9 And Ground
        G06685124Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.

      Q: Is the measured voltage battery positive voltage with the brake pedal depressed (closed circuit), and less than 1.0 volt with the brake pedal released (open circuit)? 

      1. YES:  Go to Step  12.
      2. NO:  Go to Step 10.
  10. STEP 10. Check PCM connector B-18 and joint connector (1) C-28 for loose, corroded or damaged terminals, or terminals pushed back in the connector. 

    Q: Are the connectors and terminals in good condition? 

    1. YES:  Go to Step 11.
    2. NO:  Repair or replace the damaged components. Refer to HARNESS CONNECTOR INSPECTION .
      Fig 12: Locating PCM Connector B-18
      G06685122Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
      Fig 13: Locating Joint Connector C-28
      G04231095Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
  11. STEP 11. Check the harness for damage between PCM connector B-18 terminal 9 and stoplight switch connector C-103 terminal 1. 

    Q: Is the harness wire in good condition? 

    1. YES:  Go to Step 12.
    2. NO:  Repair or replace the harness wire.
      Fig 14: Locating PCM Connector B-18
      G06685122Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
      Fig 15: Locating Stoplight Switch Connector C-103
      G06685115Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
  12. STEP 12. Using scan tool MB991958, check data list item 19: Stoplight Switch. 
    CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.
    1. Connect scan tool MB991958 to the data link connector.
    2. Turn the ignition switch to the "ON" position.
    3. Set scan tool MB991958 to the data reading mode.
      • Item 19: Stoplight Switch.
        • When the brake pedal is depressed, the display on scan tool MB991958 should be "ON."
        • When the brake pedal is not depressed, the display on scan tool MB991958 should be "OFF."
    4. Turn the ignition switch to the "LOCK" (OFF) position.
      Fig 16: Connecting Special Tool MB991910 To Data Link Connector
      G04230562Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.

      Q: Is the switch operating properly? 

      1. YES:  It can be assumed that this malfunction may be intermittent. Refer to HOW TO COPE WITH INTERMITTENT MALFUNCTION .
      2. NO:  Replace the PCM. When the PCM is replaced, register the encrypted code. Refer to ENCRYPTED CODE REGISTRATION CRITERIA TABLE .
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