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DTC P1025/16509 - Insufficient Coolant Temp. For Closed Loop Fuel Control

NOTE: DTC is set when Electronic Control Module (ECM) cannot use engine coolant temperature signal for Heated Oxygen Sensor (HO2S) control, or time taken for engine to reach normal operating temperature is too long.
  1. Check Engine Coolant Temperature (ECT) sensor circuit. See DTCs P0117/16501 and P0118/16502. Repair ECT sensor circuit as necessary. Erase DTC memory and test drive vehicle. See CLEARING DTCS in this article. Recheck DTC memory and verify DTC does not reset. If DTC resets, go to next step. If ECT sensor circuit is okay, go to next step.
  2. Replace faulty thermostat. Clear DTCs and perform test drive. See CLEARING DTCS  in this article. Recheck DTC memory and verify DTC does not reset. If DTC resets, go to next step.
  3. Replace faulty ECM. Test drive vehicle. Recheck DTC memory and verify DTC does not reset. If DTC resets, repeat testing procedure.
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