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DTC 30: Brake Light Relay Circuit Malfunction

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  1. Check the brake lights without pressing the brake pedal.

    Are the brake lights off? 

    YES  -Go to step  10.

    NO  -Go to step 2.

  2. Check the brake pedal height, and adjust it if needed (see BRAKE PEDAL AND BRAKE PEDAL POSITION SWITCH ADJUSTMENT ).
  3. Check the brake lights without pressing the brake pedal.

    Are the brake lights off? 

    YES  -Intermittent failure, the system is OK at this time. Check for loose or poor connections.

    NO  -Go to step 4.

  4. Test the brake pedal position switch (see HIGH MOUNT BRAKE LIGHT REPLACEMENT ).

    Is the brake pedal position switch OK? 

    YES  -Go to step 5.

    NO  -Adjust or replace the brake pedal position switch, and recheck (see BRAKE PEDAL REPLACEMENT ).

  5. Test the brake light relay (see POWER RELAY TEST ).

    Is the relay OK? 

    YES  -Go to step 6.

    NO  -Replace the relay, and recheck.

  6. Disconnect the brake pedal position switch 4P connector.
  7. Measure the voltage between brake pedal position switch 4P connector terminal No. 2 and body ground.
    Fig 1: Measuring Voltage Between Brake Pedal Position Switch 4P Connector Terminal No. 2 And Body Ground
    G08058568Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there battery voltage? 

    YES  -Repair a short to power in the wire between the brake pedal position switch and the brake light relay.

    NO  -Go to step 8.

  8. Disconnect the ACC unit 20P connector.
  9. Measure the voltage between ACC unit 20P connector terminal No. 1 and body ground.
    Fig 2: Measuring Voltage Between ACC Unit 20P Connector Terminal No. 1 And Body Ground
    G08058569Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there battery voltage? 

    YES  -Repair a short to power in the wire between the ACC unit and the brake light relay, or between the ACC unit and the brake lights circuits.

    NO  -Check for loose or poor connections. If OK, update the ACC unit (see ACC UNIT UPDATE  ), then recheck. If the ACC unit was already updated, replace the ACC unit (see ADAPTIVE CRUISE CONTROL (ACC) UNIT REMOVAL/INSTALLATION  ).

  10. Clear the DTCs with the HDS (see HOW TO CLEAR DTCS  ).
  11. Press the MAIN switch ON.
  12. Check the brake lights with the brake pedal pressed.

    Do the brake lights come on? 

    YES  -Go to step 13.

    NO  -Go to step  37.

  13. Check for DTCs with the HDS (see HOW TO CLEAR DTCS  ).

    Is DTC 30 indicated? 

    YES  -Go to step 14.

    NO  -Go to step  21.

  14. Turn the ignition switch to LOCK (0).
  15. Remove the brake light relay.
  16. Disconnect the ACC unit 20P connector.
  17. Disconnect the VSA modulator-control unit 46P connector (see VSA MODULATOR-CONTROL UNIT REMOVAL AND INSTALLATION ).
  18. Disconnect both rear taillight connectors from the taillights and, if equipped, the trailer light harness connector from the rear fuse box.
  19. Measure the resistance between ACC unit 20P connector terminal No. 1 and body ground. There should be an open circuit or at least 1 MΩ.
    Fig 3: Measuring Resistance Between ACC Unit 20P Connector Terminal No. 1 And Body Ground
    G08058570Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is the resistance as specified? 

    YES  -Go to step 20.

    NO  -Repair a short to ground in the wire between the ACC unit and the brake light relay, or between the ACC unit and the brake lights circuits.

  20. Measure the resistance between ACC unit 20P connector terminal No. 1 and brake light relay 5P connector terminal No. 1. There should be less than 1.0 Ω.
    Fig 4: Measuring Resistance Between ACC Unit 20P Connector And Brake Light Relay 5P Connector
    G08058571Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is the resistance as specified? 

    YES  -Check for loose or poor connections. If OK, update the ACC unit (see ACC UNIT UPDATE  ), then recheck. If the ACC unit was already updated, replace the ACC unit (see ADAPTIVE CRUISE CONTROL (ACC) UNIT REMOVAL/INSTALLATION  ).

    NO  -Repair an open in the wire between the ACC unit and the brake light relay.

  21. Test the brake light relay (see POWER RELAY TEST ).

    Is the relay OK? 

    YES  -Go to step 22.

    NO  -Replace the relay, and recheck.

  22. Remove the brake light relay.
  23. Measure the voltage between brake light relay 5P connector terminal No. 2 and body ground. There should be battery voltage.
    Fig 5: Measuring Voltage Between Brake Light Relay 5P Connector Terminal No. 2 And Body Ground
    G08058572Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there battery voltage? 

    YES  -Go to step 24.

    NO  -Repair an open in the wire between the No. 11 (15 A) fuse in the main under-hood fuse box and the brake light relay.

  24. Turn the ignition switch to ON (II).
  25. Measure the voltage between brake light relay 5P connector terminal No. 5 and body ground. There should be battery voltage,
    Fig 6: Measuring Voltage Between Brake Light Relay 5P Connector Terminal No. 5 And Body Ground
    G08058573Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there battery voltage? 

    YES  -Go to step 26.

    NO  -Repair an open in the wire between the No. 21 (7.5 A) fuse in the under-dash fuse/relay box and the brake light relay.

  26. Turn the ignition switch to LOCK (0).
  27. Disconnect the ACC unit 20P connector.
  28. Measure the resistance between ACC unit 20P connector terminal No. 16 and body ground. There should be an open circuit or at least 1 MΩ.
    Fig 7: Measuring Resistance Between ACC Unit 20P Connector Terminal No. 16 And Body Ground
    G08058574Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is the resistance as specified? 

    YES  -Go to step 29.

    NO  -Repair a short to ground in the wire between the ACC unit and the brake light relay.

  29. Measure the resistance between ACC unit 20P connector terminal No. 16 and brake light relay 5P connector terminal No. 3. There should be less than 1.0 Ω.
    Fig 8: Measuring Resistance Between ACC Unit 20P Connector And Brake Light Relay 5P Connector
    G08058575Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is the resistance as specified? 

    YES  -Go to step 30.

    NO  -Repair an open in the wire between the ACC unit and the brake light relay.

  30. Install the brake light relay.
  31. Reconnect the ACC unit 20P connector.
  32. Clear the DTCs with the HDS (see HOW TO CLEAR DTCS  ).
  33. Turn the ignition switch to ON (II), then wait for 10 seconds, and press the MAIN switch ON.
  34. Select ADAPTIVE CRUISE CONTROL (ACC) from the DRIVING SUPPORT menu, then enter ACC RELAY from the FUNCTION TEST menu.
  35. Do the brake light relay function test with the HDS.
  36. Check for DTCs with the HDS (see HOW TO CLEAR DTCS  ).

    Is DTC 30 indicated? 

    YES  -Check for loose or poor connections. If OK, update the ACC unit (see ACC UNIT UPDATE  ), then recheck. If the ACC unit was already updated, replace the ACC unit (see ADAPTIVE CRUISE CONTROL (ACC) UNIT REMOVAL/INSTALLATION  ).

    NO  -Troubleshoot the indicated DTC(s). If there are no DTCs, the system is OK at this time.

  37. Check for DTCs with the HDS (see HOW TO CLEAR DTCS  ).

    Is DTC 30 indicated? 

    YES  -Go to step 38.

    NO  -Go to step  44.

  38. Test the brake light relay (see POWER RELAY TEST ).

    Is the relay OK? 

    YES  -Go to step 39.

    NO  -Replace the relay, and recheck.

  39. Remove the brake light relay.
  40. Disconnect the ACC unit 20P connector.
  41. Disconnect each taillight 3P connector and the high mount brake light 2P connector.
  42. Measure the resistance between ACC unit 20P connector terminal No. 1 and body ground. There should be an open circuit or at least 1 MΩ.
    Fig 9: Measuring Resistance Between ACC Unit 20P Connector Terminal No. 1 And Body Ground
    G08058576Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is the resistance as specified? 

    YES  -Go to step 43.

    NO  -Repair a short to ground in the wire between the ACC unit and the brake light relay, or between the ACC unit and the brake lights circuits.

  43. Measure the resistance between ACC unit 20P connector terminal No. 1 and brake light relay 5P connector terminal No. 1. There should be less than 1.0 Ω.
    Fig 10: Measuring Resistance Between ACC Unit 20P Connector And Brake Light Relay 5P Connector
    G08058577Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is the resistance as specified? 

    YES  -Check for loose or poor connections. If OK, update the ACC unit (see ACC UNIT UPDATE  ), then recheck. If the ACC unit was already updated, replace the ACC unit (see ADAPTIVE CRUISE CONTROL (ACC) UNIT REMOVAL/INSTALLATION  ).

    NO  -Repair an open in the wire between the ACC unit and the brake light relay.

  44. Check the brake pedal height, and adjust it if needed (see BRAKE PEDAL AND BRAKE PEDAL POSITION SWITCH ADJUSTMENT ).
  45. Test the brake pedal position switch (see HIGH MOUNT BRAKE LIGHT REPLACEMENT ).
  46. Check the brake lights with the brake pedal pressed.

    Do the brake lights come on? 

    YES  -Intermittent failure, the system is OK at this time. Check for loose or poor connections.

    NO  -Repair an open in the wire or poor ground (G701, G702).

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