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Home >> Toyota >> 2003 >> Matrix Base, FWD, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Self Diagnostics >> Diagnostic Tests >> DTC P0128: Thermostat Malfunction (Corolla Model) >> Diagnosis & Repair
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Diagnosis & Repair

NOTE: Read freeze frame data using hand-held tester or OBD II scan tool, as freeze frame data records engine conditions when malfunction is detected. When trouble shooting, it is useful for determining whether vehicle was running or stopped, engine was warmed up or not, air-fuel ratio was lean or rich, etc. at time of malfunction.
  1. Check thermostat. See appropriate article in ENGINES. If results are OK, go to next step. If results are not good, replace thermostat. See appropriate article in ENGINES.
  2. Check if DTC (besides P0128) are output. If DTC P0128 and other codes are output, diagnose and repair those codes first. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If only DTC P0128 is output, check and replace ECM. To check ECM inputs and outputs, see PIN VOLTAGE CHARTS article. To replace ECM, see REMOVAL & INSTALLATION - 4-CYLINDER article.
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