DTC 22: Stoplight Switch System: Diagnosis

Required Special Tools: 

• MB991223: Harness Set
• MB991502: Scan Tool (MUT-II)

1. STEP 1. Check the brake pedal height. 

   Refer to ADJUSTMENTS .

   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. Using scan tool MB991502, read the diagnostic trouble code. 
   CAUTION: To prevent damage to scan tool MB991502, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991502.
   1. Connect scan tool MB991502 to the data link connector.
      Fig 1: Connecting Scan Tool MB991502 To Data Link Connector

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   2. Turn the ignition switch to the "ON" position.
   3. Check for A/T system diagnostic trouble code.
   4. Turn the ignition switch to the "LOCK" (OFF) position.

   Q: Is DTC 26 set? 

   1. YES :  Refer to Diagnostic Trouble Code Procedures - DTC 26: STOPLIGHT SWITCH SYSTEM .
   2. NO :  Go to Step 3.
3. STEP 3. Using scan tool MB991502, check data list item 06: Stoplight Switch. 
   CAUTION: To prevent damage to scan tool MB991502, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991502.
   1. Connect scan tool MB991502 to the data link connector.
      Fig 2: Checking Data List Item 06 Stoplight Switch Using Scan Tool

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   2. Turn the ignition switch to the "ON" position.
   3. Set scan tool MB991502 to data reading mode for auto-cruise control system item 06, Stoplight Switch.
      • When the brake pedal is depressed, the display on scan tool MB991502 should be "ON."
      • When the brake pedal is not depressed, the display on scan tool MB991502 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 is intermittent. Refer to HOW TO USE TROUBLESHOOTING/ INSPECTION SERVICE POINTS - How to Cope with Intermittent Malfunction .
   2. NO :  Go to Step 4.
4. STEP 4. Check stoplight switch connector D-123 for looser, corroded or damaged terminals, or terminals pushed back in the connector. 
   Fig 3: Identifying Stoplight Switch Connector D-123 Location And Terminal View

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   Q: Are the connector and terminals in good condition? 

   1. YES :  Go to Step 5.
   2. NO :  Repair or replace the damaged components. Refer to HARNESS CONNECTOR INSPECTION .
5. STEP 5. Measure the stoplight switch power supply voltage at connector D-123 by backprobing. 
   1. Do not disconnect connector D-123.
      Fig 4: Identifying Stoplight Switch Connector D-123 Location And Terminal View

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   2. Turn the ignition switch to the "ON" position.
   3. Measure the voltage between terminal 3 and ground by backprobing.
      • 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 volt.
   Fig 5: Measuring Stoplight Switch Power Supply Voltage

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   Q: Does the voltage measure the battery positive voltage when the brake pedal is depressed, and measure one volt or less when the pedal is released? 

   1. YES :  Go to Step  8 .
   2. NO :  Go to Step 6.
6. STEP 6. Check stoplight switch connector D-123, intermediate connector D-125, intermediate connector E-110 and PCM connector D-133 for looser, corroded or damaged terminals, or terminals pushed back in the connector. 
   Fig 6: Identifying Stoplight Switch Connector D-123 Location And Terminal View

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   Fig 7: Identifying Intermediate Connector D-125 Location And Terminal View

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   Fig 8: Identifying Intermediate Connector E-110 Location And Terminal View

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   Fig 9: Identifying PCM Connector D-133 Location And Terminal View

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   Q: Are the connectors and terminals in good condition? 

   1. YES :  Go to Step 7.
   2. NO :  Repair or replace the damaged components. Refer to HARNESS CONNECTOR INSPECTION .
7. STEP 7. Check the harness for an open circuit or damage between stoplight switch connector D-123 terminal 3 and PCM connector D-133 terminal 54. 
   Fig 10: Identifying Stoplight Switch Connector D-123 Location And Terminal 3 View

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   Fig 11: Identifying PCM Connector D-133 Location And Terminal 54 View

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   Q: Is the harness wire in good condition? 

   1. YES :  Go to Step 8.
   2. NO :  Repair or replace the harness wire.
8. STEP 8. Check the resistance of the ground circuit at stoplight switch connector D-123. 
   1. Disconnect stoplight switch connector D-123 and measure at the harness side.
      Fig 12: Identifying Stoplight Switch Connector D-123 Location And Terminal View

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   2. Check the resistance between terminal 4 and ground.
      • The resistance should measure less than 2 ohms.
   Fig 13: Checking Resistance Of Ground Circuit

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   Q: Is the resistance less than 2 ohms? 

   1. YES :  Go to Step  10 .
   2. NO :  Go to Step 9.
9. STEP 9. Check the harness for an open circuit or damage between stoplight switch connector D-123 terminal 4 and ground. 
   Fig 14: Identifying Stoplight Switch Connector D-123 Location And Terminal View

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   Q: Is the harness wire in good condition? 

   1. YES :  Go to Step 10.
   2. NO :  Repair or replace the harness wire.
10. STEP 10. Check the stoplight switch. 
    1. Disconnect stoplight switch connector D-123.
    2. Remove the stoplight switch and measure at the stoplight switch side.
       Fig 15: Identifying Stoplight Switch Connector D-123 Location And Terminal View

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    3. Measure the resistance value between terminals 3 and 4.
       Fig 16: Checking Stoplight Switch

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       • The resistance value should measure two ohms or less when the plunger is pushed within 4.5 mm (0.2 inch) from the outer case end.
       Fig 17: Identifying Plunger Position To Measuring Resistance

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    Q: Does the resistance value measure two ohms or less when the plunger is pushed within 4.5 mm (0.2 inch) from the outer case end? 

    YES:  Go to Step 11.

    NO :  Replace the stoplight switch. Refer to DISC article. .

11. STEP 11. Using scan tool MB991502, check data list item 06: Stoplight Switch. 
    CAUTION: To prevent damage to scan tool MB991502, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991502.
    1. Connect scan tool MB991502 to the data link connector.
       Fig 18: Connecting Scan Tool MB991502 To Data Link Connector

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    2. Turn the ignition switch to the "ON" position.
    3. Set scan tool MB991502 to data reading mode for auto-cruise control system item 06, Stoplight Switch.
       • When the brake pedal is depressed, the display on scan tool MB991502 should be "ON."
       • When the brake pedal is not depressed, the display on scan tool MB991502 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 is intermittent. Refer to HOW TO USE TROUBLESHOOTING/ INSPECTION SERVICE POINTS - How to Cope with Intermittent Malfunction .
    2. NO :  Replace the PCM. Refer to AUTO-CRUISE CONTROL