LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Jaguar >> 2000 >> XJ8 Base >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Trouble Code Identification >> DTC P1571: Brake Switch Malfunction >> Diagnostic Test Procedure
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Diagnostic Test Procedure

  1. Disconnect negative battery cable. Disconnect the brake switch connector. Disconnect ECM connector EM82. Measure resistance between brake switch harness connector terminal No. 1 and ECM harness connector EM82 terminal No. 8. Is resistance greater than 5 ohms? If yes, repair high resistance between brake switch harness connector terminal No. 1 and ECM harness connector EM82 terminal No. 8. If no, go to next step.
  2. Reconnect negative battery cable. Turn ignition on. Measure voltage between brake switch harness connector terminal No. 1 and ground. Is voltage greater than 3 volts? If yes, repair short to voltage. If no, go to next step.
  3. Turn ignition off. Measure resistance between brake switch harness connector terminal No. 1 and ground. Is resistance less than 10,000 ohms? If yes, repair short to ground. If no, go to next step.
  4. Disconnect ignition switch connector. Measure resistance between brake switch harness connector terminal No. 4 and ignition switch harness connector terminal No. 3. Is resistance greater than 5 ohms? If yes, repair high resistance between brake switch harness connector terminal No. 4 and ignition switch harness connector terminal No. 3. If no, go to next step.
  5. Measure resistance between brake switch terminals No. 1 and 4. Operate the brake pedal up and down. Does resistance switch between open circuit and continuity as pedal is operated? If yes, go to next step. If no, install a new brake switch.
  6. Disconnect negative battery cable. Disconnect ECM connector EM80. Measure resistance between brake switch harness connector terminal No. 2 (brake cancel circuit) and ECM harness connector EM80 terminal No. 20. Is resistance greater than 5 ohms? If yes, repair high resistance between brake switch harness connector terminal No. 2 and ECM harness connector EM80 terminal No. 20. If no, go to next step.
  7. Reconnect the battery negative terminal. Turn ignition on. Measure voltage between brake switch harness connector terminal No. 2 (brake cancel circuit) and ground. Is voltage greater than 3 volts? If yes, repair short to voltage. If no, go to next step.
  8. Turn ignition off. Measure resistance between brake switch harness connector terminal No. 2 (brake cancel circuit) and ground. Is resistance less than 10,000 ohms? If yes, repair short between brake switch harness connector terminal No. 2 and ground. If no, go to next step.
  9. Disconnect negative battery cable. Disconnect cruise control switch connector. Disconnect ECM connector EM81. Measure resistance between cruise control switch harness connector terminal No. 9 and ECM harness connector EM81 terminal No. 13. Is resistance greater than 5 ohms? If yes, repair high resistance between cruise control switch harness connector terminal No. 9 and ECM harness connector EM81 terminal No. 13. If no, go to next step.
  10. Reconnect negative battery cable. Turn ignition on. Measure voltage between cruise control switch harness connector terminal No. 9 and ground. Is voltage greater than 3 volts? If yes, repair short to voltage. If no, go to next step.
  11. Turn ignition off. Measure resistance between cruise control switch harness connector terminal No. 9 and ground. Is resistance less than 10,000 ohms? If yes, repair short between cruise control switch harness connector terminal No. 9 and ground. If no, go to next step.
  12. Turn ignition on. Measure voltage between cruise control switch harness connector terminal No. 8 and ground. Is voltage less than 10 volts? If yes, repair circuit between the cruise control switch and ignition switch. If no, go to next step.
  13. Measure resistance between brake switch terminals No. 2 and 3 (brake cancel circuit). Operate the brake pedal up and down. Does resistance switch between open circuit and continuity as pedal is operated? If yes, clear codes and recheck system for other speed control circuits that will set DTCs, indicating the component at fault. If resistance does not switch between open circuit and continuity as pedal is operated, install a new brake switch.
scientia non olet · About LEMON Manuals