Diagnostic Procedure For Multiplex Communication Circuit

WARNING: This page is about a different car, the 2004 Infiniti M45. However, it is still accessible from the selected car via links, so may be relevant.

SYMPTOM:

A/C system does not come on.
A/C system cannot be controlled.

Fig 1: Identifying Multiplex Communication Circuit
Courtesy of NISSAN MOTOR CO., U.S.A.

CHECK FOR AUTO AMP. OUTPUT
1. Turn ignition switch ON.
2. Confirm multiplex communication signal between auto amp. harness connector M119 terminal 9 (W), 20 (B) and ground using an oscilloscope.
  
  Fig 2: Checking Auto Amp. Signal Using Oscilloscope
  Courtesy of NISSAN MOTOR CO., U.S.A.
  
  Fig 3: Confirming Multiplex Communication Signal Using Oscilloscope
  Courtesy of NISSAN MOTOR CO., U.S.A.
OK or NG
1. OK: GO TO 2.
2. NG: Replace auto amp.
CHECK CIRCUIT CONTINUITY BETWEEN AV C/U (AV AND NAVI C/U) AND AUTO AMP.
1. Turn ignition switch OFF.
2. Disconnect AV C/U (AV and NAVI C/U) and auto amp. connector.
3. Check continuity between AV and NAVI C/U harness connector B29 terminals 37 (L/W), 39 (L/R) or AV C/U harness connector M77 terminals 44 (L/W), 45 (L/R) and auto amp. harness connector M119 terminals 9 (L/W), 20 (L/R).
  
  Fig 4: Checking AV C/U (AV & NAVI C/U)-To-Auto Amp. Continuity
  Courtesy of NISSAN MOTOR CO., U.S.A.
  
  Fig 5: Determining Continuity Based On Switch Position
  Courtesy of NISSAN MOTOR CO., U.S.A.
OK or NG
1. OK: GO TO 3
2. NG: Repair harness or connector.
CHECK FOR AUTO AMP. INPUT
1. Reconnect AV C/U (AV and NAVI C/U) and auto amp. connector.
2. Turn ignition switch ON.
3. Confirm multiplex communication signal between auto amp. harness connector M119 terminal 10 (R) and ground using an oscilloscope.
  
  Fig 6: Checking Auto Amp. Signal Using Oscilloscope
  Courtesy of NISSAN MOTOR CO., U.S.A.
  
  Fig 7: Confirming Multiplex Communication Signal Using Oscilloscope
  Courtesy of NISSAN MOTOR CO., U.S.A.
OK or NG
1. OK: GO TO 2.
2. NG: GO TO 4.
CHECK CIRCUIT CONTINUITY BETWEEN AV C/U (AV AND NAVI C/U) AND AUTO AMP.
1. Turn ignition switch OFF.
2. Disconnect AV C/U (AV and NAVI C/U) and auto amp. connector.
3. Check continuity between AV and NAVI C/U harness connector B29 terminal 38 (L) or AV C/U harness connector M77 terminal 43 (L) and auto amp. harness connector M119 terminal 10 (L).
  
  Fig 8: Checking AV C/U (AV & NAVI C/U)-To-Auto Amp. Continuity
  Courtesy of NISSAN MOTOR CO., U.S.A.
  
  38 - 10: continuity should exist.
  
  43 - 10: continuity should exist.
OK or NG
1. OK: Replace auto amp.
2. NG: Repair harness or connector.