LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Infiniti >> 2004 >> QX56 AWD >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System >> DTC P1805: Brake Switch >> Diagnostic Procedure
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Diagnostic Procedure

  1. CHECK STOP LAMP SWITCH CIRCUIT 
    1. Turn ignition switch OFF.
    2. Check the stop lamp when depressing and releasing the brake pedal.
    BRAKE PEDAL POSITION

    Brake pedal Stop lamp
    Fully released Not illuminated
    Depressed Illuminated

    OK or NG

    OK: GO TO  4.

    NG: GO TO 2.

  2. CHECK STOP LAMP SWITCH POWER SUPPLY CIRCUIT 
    1. Disconnect stop lamp switch harness connector.
      Fig 1: Locating ASCD Brake Switch, Stop Lamp Switch & Brake Pedal
      G02691850Courtesy of NISSAN MOTOR CO., U.S.A.
    2. Check voltage between stop lamp switch terminal 1 and ground with CONSULT-II or tester.

    Voltage: Battery voltage 

    OK or NG

    OK: GO TO  4.

    NG: GO TO 3.

    Fig 2: Checking Voltage Between Stop Lamp Switch Terminal 1 & Ground
    G02691851Courtesy of NISSAN MOTOR CO., U.S.A.
  3. DETECT MALFUNCTIONING PART 

    Check the following.

    • Harness connectors M31, E152
    • Fuse block (J/B) connector M60
    • 10A fuse
    • Harness for open and short between stop lamp switch and fuse

      : Repair open circuit or short to ground or short to power in harness or connectors.

  4. CHECK STOP LAMP SWITCH INPUT SIGNAL CIRCUIT FOR OPEN AND SHORT 
    1. Turn ignition switch OFF.
    2. Disconnect ECM harness connector.
    3. Check harness continuity between ECM terminal 101 and stop lamp switch terminal 2. Refer to Wiring Diagram.

      Continuity should exist. 

    4. Also check harness for short to ground and short to power.

    OK or NG

    OK: GO TO 5.

    NG: Repair open circuit or short to ground or short to power in harness or connectors.

  5. CHECK STOP LAMP SWITCH 

    Refer to COMPONENT INSPECTION .

    OK or NG

    OK: GO TO 7.

    NG: Replace stop lamp switch.

  6. CHECK INTERMITTENT INCIDENT 

    Refer to TROUBLE DIAGNOSIS FOR INTERMITTENT INCIDENT .

    : INSPECTION END