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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 P0125: Insufficient Coolant Temperature For Closed Loop Fuel Control › 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  6. If repair information is not available, go to next step.
  2. Start engine and let it idle until it reaches normal operation temperature. Using New Generation Star (NGS) tester or equivalent, monitor ECT PID. If ECT PID is below 140°F (60°C), go to next step. If ECT PID is above 140°F (60°C), problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES article.
  3. Turn ignition off. Disconnect ECT sensor 3-pin harness connector. See Figure. Check ECTsensor for poor connection 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  6.
  4. With ECT sensor harness connector disconnected, measure resistance between ECT sensor connector terminals "A" and "B" (component side). Resistance should be 2.27-2.74 k/ohms at 68°F (20°C). If resistance is as specified, go to next step. If resistance is not as specified, replace ECT sensor. After repair, go to step  6.
  5. Leave ECT sensor harness connector disconnected and disconnect PCM 31-pin harness connector. See Figure. Check PCM harness connector terminal "4P" and "4O" for poor connection 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. For circuit identification, see MIATA in WIRING DIAGRAMS article. After repair, go to next step.
  6. Return vehicle to original condition. Using NGS tester or equivalent, clear DTCs from PCM memory. Access ECT PID and wait until ECT PID is below 68°F (20°C). Start engine and let it idle until it reaches normal operation temperature. Monitor for pending DTCs. If same DTC P0125 is present, replace PCM. For PCM removal and installation, see POWERTRAIN CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL, OVERHAUL & INSTALLATION article. If any other DTC is present, follow appropriate DTC diagnostic procedure.
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