DTC DETECTING CONDITION: Detected when two consecutive driving cycles with fault occur. TROUBLE SYMPTOM: Thermostat remains open. CAUTION: After servicing or replacing faulty parts, perform Clear Memory Mode Clear Memory Mode > OPERATION, and Inspection Mode Inspection Mode > PROCEDURE. | STEP | CHECK | YES | NO | 1.CHECK FOR ANY OTHER DTC ON DISPLAY. | Is any other DTC displayed- | Check the appropriate DTC using the “List of Diagnostic Trouble Code (DTC)”. List of Diagnostic Trouble Code (DTC) | Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC P0128 COOLANT THERMOSTAT (ENGINE COOLANT TEMPERATURE BELOW THERMOSTAT REGULATING TEMPERATURE) | | Is the engine coolant amount normal- | Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC P0128 COOLANT THERMOSTAT (ENGINE COOLANT TEMPERATURE BELOW THERMOSTAT REGULATING TEMPERATURE) | Refill the engine coolant. Engine Coolant | 3.CHECK RADIATOR FAN. 2) Check the radiator fan operation. | Does the radiator fan continuously rotate for 3 minutes or more during idling- | Repair radiator fan circuit. Radiator Fan and Fan Motor Assembly | Replace the thermostat. Thermostat |
1. OUTLINE OF DIAGNOSIS Detect malfunctions of the thermostat function. Judge as NG when any one of the following conditions is established. • When the actual engine coolant temperature does not reach the maximum temperature necessary to perform other OBDII diagnosis and Σ (Estimated engine coolant temperature − actual engine coolant temperature) exceeded the predetermined value. (Judgment 1) • When the actual engine coolant temperature does not reach the range within −11°C (−19.8°F) from the regulated temperature and Σ (Estimated engine coolant temperature − actual engine coolant temperature) exceeded the predetermined value. (Judgment 2) • When the difference between the estimated coolant temperature and the actual engine coolant temperature exceeds the predetermined value, and Σ (Estimated engine coolant temperature − actual engine coolant temperature) exceeded the predetermined value. (Judgment 3) 2. COMPONENT DESCRIPTION (1) | Jiggle valve | (5) | Dust seal | (9) | Bypass spring | (2) | Piston | (6) | Main spring | (10) | Bypass valve | (3) | Flange | (7) | Wax element | (11) | Stop ring | (4) | Stop ring | (8) | Frame | | |
3. EXECUTION CONDITION Secondary Parameters | Execution condition | | Battery voltage | ≥ 10.9 V | Ambient air temperature | ≥ −7 °C (19.4 °F) | Vehicle speed | ≥ 30 km/h (18.6 MPH) | Estimated coolant temperature | ≥ Value of Map 1 | Engine coolant temperature at engine starting | < 63 °C (145.4 °F) | | Battery voltage | ≥ 10.9 V | Ambient air temperature | ≥ −7 °C (19.4 °F) | Vehicle speed | ≥ 30 km/h (18.6 MPH) | Estimated coolant temperature | ≥ Value from Map 2 | Engine coolant temperature at engine starting | < 63 °C (145.4 °F) | | Battery voltage | ≥ 10.9 V | Ambient air temperature | ≥ −7 °C (19.4 °F) | Vehicle speed | ≥ 30 km/h (18.6 MPH) | Estimated coolant temperature | ≥ Value from Map 3 | Engine coolant temperature at engine starting | < 63 °C (145.4 °F) |
Map 1Engine coolant temperature at engine starting °C (°F) | −7 (19.4) | 8 (46.4) | 10 (50) | 25 (77) | Estimated coolant temperature °C (°F) | 60 (140) | 60 (140) | 60 (140) | 60 (140) | Map 2Engine coolant temperature at engine starting °C (°F) | −7 (19.4) | 8 (46.4) | 10 (50) | 25 (77) | Estimated coolant temperature °C (°F) | 73.5 (164.3) | 82.7 (180.9) | 82.7 (180.9) | 82.7 (180.9) | Map 3Engine coolant temperature at engine starting °C (°F) | −7 (19.4) | 10 (50) | 25 (77) | 33.5 (92.3) | Estimated coolant temperature °C (°F) | 46 (114.8) | 57 (134.6) | 72 (161.6) | 82.7 (180.9) | 4. GENERAL DRIVING CYCLE Perform the diagnosis only once after starting the engine. 5. DIAGNOSTIC METHOD If the duration of time while the following conditions are met is longer than the time indicated, judge as NG. Judgment ValueMalfunction Criteria | Threshold Value | When any one of the followings is established: | | Actual engine coolant temperature | < Value of Map 4 | and | | Σ (Estimated engine coolant temperature − actual engine coolant temperature) | > Value of Map 5 | | Actual engine coolant temperature | < Regulated temperature − Value of Map 6 | and | | Σ (Estimated engine coolant temperature − actual engine coolant temperature) | > Value of Map 7 | | Estimated engine coolant temperature − actual engine coolant temperature | > Value of Map 8 | and | | Σ (Estimated engine coolant temperature − actual engine coolant temperature) | > Value of Map 9 | Map 4Estimate ambient temperature °C (°F) | −7 (19.4) | 8 (46.4) | 10 (50) | 25 (77) | Threshold Value °C (°F) | 60 (140) | 60 (140) | 60 (140) | 60 (140) | Map 5Engine coolant temperature at engine starting °C (°F) | −7 (19.4) | 0 (32) | 8 (46.4) | 10 (50) | 30 (86) | 40 (104) | Threshold Value °C (°F) | 1731.6 (3116.9) | 1731.6 (3116.9) | 1731.6 (3116.9) | 1731.6 (3116.9) | 1731.6 (3116.9) | 1200 (2160) | Map 6Estimate ambient temperature °C (°F) | −7 (19.4) | 8 (46.4) | 10 (50) | 25 (77) | Threshold Value °C (°F) | 20.3 (36.5) | 11.1 (20) | 11.1 (20) | 11.1 (20) | Map 7Engine coolant temperature at engine starting °C (°F) | −7 (19.4) | 0 (32) | 8 (46.4) | 10 (50) | 30 (86) | 35 (95) | Threshold Value °C (°F) | 1731.6 (3116.9) | 1731.6 (3116.9) | 1731.6 (3116.9) | 1731.6 (3116.9) | 1731.6 (3116.9) | 1500 (2700) | Map 8Estimate ambient temperature °C (°F) | −7 (19.4) | 8 (46.4) | 10 (50) | 25 (77) | Threshold Value °C (°F) | 11.1 (20) | 11.1 (20) | 11.1 (20) | 11.1 (20) | Map 9Engine coolant temperature at engine starting °C (°F) | −7 (19.4) | 8 (46.4) | 10 (50) | 25 (77) | Threshold Value °C (°F) | 1731.6 (3116.9) | 1731.6 (3116.9) | 1731.6 (3116.9) | 1731.6 (3116.9) | Time Needed for Diagnosis: Less than 1 second Malfunction Indicator Light Illumination: Illuminates when malfunction occurs in 2 continuous driving cycles. | 
Dtc p0851 park/neutral switch input circuit low