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Home >> Mazda >> 2002 >> MX-5 Miata Base, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P1602: Immobilizer Unit-Pcm Communication Line Error >> Diagnostic Procedure

Diagnostic Procedure

  1. Turn ignition off. Connect New Generation Star (NGS) tester or equivalent to OBD-II Data Link Connector-2 (DLC-2). See Figure. Turn ignition on. Monitor for FREEZE FRAME DATA and ensure data has been recorded. Check for service bulletins and/or other line of repair information related to this DTC. If repair information is available, perform diagnosis and repair as necessary. After repair, go to step  19. If repair information is not available, go to next step.
  2. Leave ignition on. Using NGS tester or equivalent, clear DTCs from PCM memory. Start engine and let it idle until it reaches normal operation temperature. Monitor for DTCs. If DTC P1624 is present, go to step  10. If no other DTC is present, go to next step.
  3. Turn ignition off. Disconnect immobilizer unit 12-pin harness connector. See Fig 1. Check for poor connection at immobilizer unit connector terminals due to damaged, pulled-out pins, corrosion, etc. If connector terminals are okay, go to next step. If connector terminals are found faulty, repair or replace as necessary. After repair, go to step  19.
  4. With immobilizer unit harness connector disconnected, check continuity between ground and immobilizer unit harness connector terminal "C" (Black wire). If continuity is found, go to next step. If continuity is not found, repair open circuit (in Black wire) between immobilizer unit and body ground. For circuit identification, see MIATA in WIRING DIAGRAMS article. After repair, go to step  19.
  5. Disconnect coil 2-pin harness connector. See Fig 1. Check for poor connection at coil connector terminals due to damaged, pulled-out pins, corrosion, etc. If connector terminals are okay, go to next step. If connector terminals are found faulty, repair or replace as necessary. After repair, go to step  19.
  6. With coil harness connector disconnected, check continuity between ground and coil connector terminal "A" (component side). If continuity is not found, go to next step. If continuity is found, replace coil. After repair, go to step  19.
  7. Reconnect coil harness connector and leave immobilizer unit connector disconnected. Check continuity between ground and immobilizer unit harness connector terminal "F" (Yellow/Green wire). If continuity is not found, go to next step. If continuity is found, repair short circuit. After repair, go to step  19.
  8. Disconnect PCM 24-pin harness connector. See Fig 1. Check for poor connection at PCM connector terminals due to damaged, pulled-out pins, corrosion, etc. If connector terminals are okay, go to next step. If connector terminals are found faulty, repair or replace as necessary. After repair, go to step  19.
  9. With immobilizer unit and PCM harness connectors disconnected, check continuity between immobilizer unit harness connector terminal "A" and PCM harness connector terminal "3S" (Red/Black wire). If continuity is found, go to step  19. If continuity is not found, repair open circuit between immobilizer unit and PCM. After repair, go to step  19.
  10. While monitoring for other malfunction codes and DTC P1624 is been found present, also check for presence of DTC P1602. If DTC P1602 is present, go to step  14. If DTC P1602 is not present, go to next step.
  11. Turn ignition off. Disconnect coil 2-pin harness connector. See Fig 1. Check for poor connection at coil connector terminals due to damaged, pulled-out pins, corrosion, etc. If connector terminals are okay, go to next step. If connector terminals are found faulty, repair or replace as necessary. After repair, go to step  19.
  12. With coil harness connector disconnected, check continuity between coil connector terminal "A"and "B" (component side). If continuity is found, go to next step. If continuity is not found, replace coil. For circuit identification, see MIATA in WIRING DIAGRAMS article. After repair, go to step  19.
  13. Reconnect coil harness connector and disconnect immobilizer unit 12-pin harness connector. See Fig 1. Check continuity between immobilizer unit harness connector terminals "D" (Yellow/Red wire) and "F" (Yellow/Green wire). If continuity is found, go to step  19. If continuity is not found, repair open circuit (in ether Yellow/Red or Yellow/Green wire) between coil and immobilizer unit. After repair, go to step  19.
  14. Malfunction codes P1624 and P0602 are been found present in system. Now check immobilizer system for DTCs. If DTC 03 is present, check key being used, key has not transponder, replace and reprogram with registered key new key. For key reprogram, see appropriate IMMOBILIZER SYSTEMS article in ACCESSORIES & EQUIPMENT. After key being reprogrammed go to step  19. If DTC 03 is not present, go to next step.
  15. Also check immobilizer system for malfunction code 01. If DTC 01 is present, check key being used, may not be programmed to immobilizer system. Reprogram key or use another programed key. For key reprogram, see appropriate IMMOBILIZER SYSTEMS article in ACCESSORIES & EQUIPMENT. After key being reprogrammed go to next step. If DTC 01 is not present, go to next step.
  16. Turn ignition off. Disconnect immobilizer unit 10-pin harness connector. See Fig 1. Check for poor connection at immobilizer unit connector terminals due to damaged, pulled-out pins, corrosion, etc. If connector terminals are okay, go to next step. If connector terminals are found faulty, repair or replace as necessary. After repair, go to step  19.
  17. With immobilizer unit harness connector disconnected, turn ignition on. Measure voltage between ground and immobilizer unit harness connector terminal "J" (Blue/Red wire). If battery voltage is found, go to next step. If battery voltage is not found, repair open circuit (in Blue/Red wire) between immobilizer unit and inside vehicle fuse block. For circuit identification, see MIATA in WIRING DIAGRAMS article. After repair, go to step  19.
  18. Turn ignition off. With immobilizer unit harness connector disconnected, check continuity between ground and immobilizer unit harness connector terminal "A" (Red/Black wire). If continuity is not found, go to next step. If continuity is found, repair short circuit to ground (in Red/Black wire) between immobilizer unit and PCM. After repair, go to next step.
  19. Return vehicle to original condition. Using NGS tester or equivalent, clear DTCs from PCM memory. Start engine and let it idle until it reaches normal operation temperature. Monitor for DTCs. If same DTC P1602 is present, replace PCM. For PCM removal and installation, see POWERTRAIN CONTROL MODULE in REMOVAL, OVERHAUL & INSTALLATION article. If any other DTC is present, follow appropriate DTC diagnostic procedure.
Fig 1: Identifying Immobilizer Unit, Coil & Powertrain Control Module Connectors Terminals
G00162131Courtesy of MAZDA MOTORS CORP.
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