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Home >> Mazda >> 2002 >> MX-5 Miata Base, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P1518: Variable Tumble Control System Stuck Open >> 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  9. If repair information is not available, go to next step.
  2. Turn ignition off. Disconnect VTCS vacuum switch 2-pin harness connector. See Figure. Check for poor connection at VTCS vacuum switch 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  9.
  3. With VTCS vacuum switch harness connector disconnected, check continuity between ground and VTCS vacuum switch harness connector terminal "B" (Black wire). If continuity is found, go to next step. If continuity is not found, repair open circuit (in Black wire) between VTCS vacuum switch and PCM. For circuit identification, see MIATA in WIRING DIAGRAMS article. After repair, go to step  9.
  4. Inspect VTCS vacuum switch for being stuck open. See VTCS Vacuum Switch Check (Miata) at VARIABLE TUMBLE CONTROL SYSTEM (MIATA 1.8L, PROTOGE, PROTOGE5 & 626 2.0L) in VARIABLE TUMBLE CONTROL SYSTEM in SYSTEM & COMPONENT TESTING - MIATA, MILLENIA, MPV, PROTEGE, PROTEGE5 & 626 article. If VTCS vacuum switch is okay, go to next step. If VTCS vacuum switch is faulty, replace VTCS vacuum switch. After repair go step  9.
  5. Inspect VTCS solenoid valve for being stuck open. See VTCS Solenoid Check at VARIABLE TUMBLE CONTROL SYSTEM (MIATA 1.8L, PROTOGE, PROTOGE5 & 626 2.0L) in VARIABLE TUMBLE CONTROL SYSTEM in SYSTEM & COMPONENT TESTING - MIATA, MILLENIA, MPV, PROTEGE, PROTEGE5 & 626 article. If VTCS solenoid valve is okay, go to next step. If VTCS solenoid valve is faulty, replace VTCS solenoid valve. After repair go step  9.
  6. Inspect vacuum hoses for damage or misconnection. See VACUUM DIAGRAM REFERENCE in VACUUM DIAGRAMS article. If vacuum hoses are okay, go to next step. If vacuum hoses are faulty, repair or replace as necessary. After repair, go to step  9.
  7. Turn ignition off. Disconnect PCM 31-pin harness connector. See Figure. Check for poor connection at PCM connector terminals "4J" 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 and go to step  9.
  8. With VTCS vacuum switch and PCM harness connector disconnected, turn ignition on. Measure voltage between ground and PCM harness connector terminal "4J" (Orange wire). If voltage is not found, go to next step. If voltage is found, repair short circuit to voltage (in Orange wire) between VTCS vacuum switch and PCM. After repair, go to next step.
  9. 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 P1518 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.
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