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Home >> Ford >> 2000 >> Taurus LX, 3.0 2, AX4N >> Repair and Diagnosis >> External Pages >> Different car >> Section 1808 (Engine Controls - Self-Diagnostics Introduction- EEC-V - Gasoline & NGV) >> Diagnostic Monitors >> Thermostat Monitor

Thermostat Monitor

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Thermostat Monitor is designed to verify proper thermostat operation. This monitor only applies to certain applications beginning with the 2000 model year and replaces "Insufficient temperature for closed-loop test" (DTC P0125). This monitor will be executed once per drive cycle and has a monitor run duration of 300-800 seconds. If a malfunction is indicated by thermostat monitor a DTC P0125 will be set and MIL will be illuminated. The monitor checks Engine Coolant Temperature (ECT) or Cylinder Head Temperature (CHT) sensor to warm up in a predictable manner when engine is generating sufficient heat. A timer is started while engine is at moderate load and vehicle speed is above a calibrated limit. Target timer value is based on ambient air temperature at start-up. If timer exceeds the target time and ECT/CHT has not warmed up to target temperature, a malfunction is indicated. The test runs if start-up intake air temperature from IAT sensor is at, or below target temperature. A 2-hour engine off soak time is required to erase a pending or confirmed DTC. This soak time feature prevents false-passes of monitor when the engine coolant temperature rises after engine is turned off during a short engine off soak period. The target temperature will be calibrated to thermostat regulating temperature minus 20°F (11°C). For a typical 195°F (90°C) thermostat, warm-up temperature would be calibrated to 175°F (79°C).

NOTE: Vehicles not part of thermostat monitor phase-in, will utilize a 140°F (60°C) warm-up temperature.

  1. Inputs

    ECT or CHT, IAT, engine LOAD (from MAF sensor) and vehicle speed input. Typical monitor entry conditions are as follows:
    • Vehicle speed more than 15 MPH.
    • Intake air temperature at start-up is between 20°F (-7°C) and target thermostat temperature.
    • Engine load more than 30 percent.
    • Engine off (soak) time to clear pending or confirmed DTC is more than 2 hours.

  2. Output

    Malfunction Indicator Lamp (MIL)
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