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Home >> Mazda >> 2001 >> MX-5 Miata Base, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P1602: Immobilizer Unit-Pcm Communication Line Error >> Diagnosis & Repair Procedure

Diagnosis & Repair Procedure

  1. Check for related service bulletins. Repair as necessary and go to next step.
  2. Using scan tool, clear DTCs. See CLEARING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. Turn ignition off and on. Check for DTCs. If DTC P1602 is not present, go to next step. If DTC P1602 is present, go to step  10.
  3. Turn ignition off. Disconnect immobilizer unit connector. Immobilizer control unit is located above accelerator and brake pedals. Check connector for loose or damaged terminals, poor contact or corrosion. Repair as necessary and go to step  19. If no problem is found, go to next step.
  4. Check for continuity between ground and immobilizer unit harness connector terminal "C" (Black wire). See Fig 1. If continuity is present, go to next step. If continuity is not present, repair open in Black wire. See WIRING DIAGRAMS article. Go to step  19.
  5. Disconnect clock spring connector. Clock spring connector is located in steering column cover. Check connector for loose or damaged terminals, poor contact or corrosion. Repair as necessary and go to step  19. If no problem is found, go to next step.
  6. Check for continuity between ground and clock spring connector terminal "A" (Yellow/Green wire). If continuity is not present, go to next step. If continuity is present, replace clock spring and go to step  19.
  7. Reconnect clock spring connector. Check for continuity between ground and immobilizer unit harness connector terminal "F" (Yellow/Green wire). See Fig 1. If continuity is not present, go to next step. If continuity is present, repair short in Yellow/Green wire. See WIRING DIAGRAMS article. Go to step  19.
  8. Disconnect appropriate PCM connector. Check connector for loose or damaged terminals, poor contact or corrosion. Repair as necessary and go to step  19. If no problem is found, go to next step.
  9. Check for continuity of Red/Black wire between PCM harness connector terminal No. 3S and immobilizer unit harness connector terminal "A". See Figure and Fig 1 . If continuity is present, go to step  19. If continuity is not present, repair open in Red/Black wire. See WIRING DIAGRAMS article. Go to step  19.
  10. Using scan tool, ensure DTC P1602 is still present. If DTC is not present, go to next step. If DTC is still present, go to step  14.
  11. Disconnect clock spring connector. Clock spring connector is located in steering column cover. Check connector for loose or damaged terminals, poor contact or corrosion. Repair as necessary and go to step  19. If no problem is found, go to next step.
  12. Check for continuity between clock spring connector terminals. If continuity is present, go to next step. If continuity is not present, replace clock spring.
  13. Reconnect clock spring connector. Check for continuity between immobilizer unit harness connector terminals "D" (Yellow/Red wire) and "F" (Yellow/Green wire). See Fig 1. If continuity is present, go to step  19. If continuity is not present, repair open circuit and go to step  19.
  14. Check for immobilizer unit DTCs. See IMMOBILIZER SYSTEMS - MIATA article in ACCESSORIES & EQUIPMENT. If immobilizer unit DTC 3 is not present, go to next step. If immobilizer unit DTC 3 is present transponder in ignition key is malfunctioning or is missing. Replace key and go to step  19.
  15. Check for immobilizer unit DTCs. See IMMOBILIZER SYSTEMS - MIATA article in ACCESSORIES & EQUIPMENT. If immobilizer unit DTC 1 is not present, go to next step. If immobilizer unit DTC 1 is present transponder in ignition key is not or is incorrectly registered. Reprogram or replace key as necessary and go to step  19.
  16. Turn ignition off. Disconnect immobilizer unit connector. Immobilizer control unit is located above accelerator and brake pedals. Check connector for loose or damaged terminals, poor contact or corrosion. Repair as necessary and go to step  19. If no problem is found, go to next step.
  17. Turn ignition on. Measure voltage between ground and immobilizer unit harness connector terminal "J" (Blue/Red wire). See Fig 1. If battery voltage is present, go to next step. If battery voltage is not present, repair open in circuit and go to step  19.
  18. Turn ignition off. Check for continuity between ground and immobilizer unit harness connector terminal "A" (Red/Black wire). See Fig 1. If continuity is not present, go to next step. If community is present, repair short in Red/Black wire and go to next step.
  19. Reconnect all connectors. Clear DTCs. See CLEARING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. Turn ignition off. Start engine. Check for DTCs. See RETRIEVING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. If DTC P1602 is present, replace PCM and go to next step. On vehicles equipped with immobilizer system, reprogram ignition key identification numbers. See COMPUTER RELEARN PROCEDURES article in GENERAL INFORMATION. If DTC P1602 is not present, go to next step.
  20. Cycle ignition from off to on. Check for DTCs. See RETRIEVING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. If any other DTC is present, go to appropriate test.
Fig 1: Identifying Immobilizer Unit Harness Connector Terminals
G00032512Courtesy of MAZDA MOTORS CORP.
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