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Diagnosis & Repair

WARNING: This page is about a different car, the 2002 Toyota Prius. However, it is still accessible from the selected car via links, so may be relevant.
  1. Remove and inspect cooling system thermostat for damage and proper operation. Thermostat is located behind thermostat housing which is located just below the intake manifold, just above the oil filter.
  2. If thermostat is okay, ensure proper cooling system bleeding procedure is performed when filling cooling system. See COOLING SYSTEM BLEEDING under COOLING SYSTEM in REMOVAL, OVERHAUL & INSTALLATION - 4-CYLINDER article. Go to next step. If thermostat is defective, replace thermostat as necessary and retest system. Ensure proper cooling system bleeding procedure is performed when filling cooling system. See COOLING SYSTEM BLEEDING under COOLING SYSTEM in REMOVAL, OVERHAUL & INSTALLATION - 4-CYLINDER article.
  3. Using Toyota hand-held tester or scan tool, check for any other DTCs. If other DTCs exist, diagnose and repair those DTCs first and retest. If only DTC P0128 exists, replace ECM. ECM is located behind glove box. See Figure.
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