P0128
2AZ-FE ENGINE CONTROL: SFI SYSTEM: P0128: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)
P0128 - Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)
DESCRIPTION
HINT
This DTC relates to the thermostat.
This DTC is set when the engine coolant temperature does not reach 75°C (167°F) despite sufficient engine warm-up time having elapsed.
MONITOR DESCRIPTION
The ECM estimates the engine coolant temperature based on the starting temperature, engine loads, and engine speeds. The ECM then compares the estimated temperature with the actual engine coolant temperature. When the estimated engine coolant temperature reaches 75°C (167°F), the ECM checks the actual engine coolant temperature. If the actual engine coolant temperature is less than 75°C (167°F), the ECM interprets this as a malfunction in the thermostat or the engine cooling system and sets the DTC.
MONITOR STRATEGY
TYPICAL ENABLING CONDITIONS
TYPICAL MALFUNCTION THRESHOLDS
CONFIRMATION DRIVING PATTERN
1. Connect the Techstream to the DLC3.
2. Turn the ignition switch to ON and turn the Techstream on.
3. Clear the DTCs (even if no DTCs are stored, perform the clear DTC procedure) DTC Check / Clear.
4. Turn the ignition switch off for 30 seconds.
5. Turn the ignition switch to ON and turn the Techstream on [A].
6. Enter the following menus: Powertrain / Engine / Data List / All Data / Coolant Temp and Intake Air.
7. Check that "Coolant Temp" and "Intake Air" in the Data List are within the range of 0 to 35°C (32 to 95°F).
8. Heater set to MAX HOT with fresh air mode selected.
9. Start the engine and wait 15 minutes or more [B].
10. Enter the following menus: Powertrain / Engine and ECT / Trouble Codes / Pending.
11. Read Pending DTCs [C].
HINT
If a pending DTC is output, the system is malfunctioning.
HINT
- If the judgment result shows ABNORMAL, the system has a malfunction.
- If the judgment result shows INCOMPLETE or UNKNOWN, perform steps [B] and [C].
12. If the test result is UNKNOWN, enter the following menus: Powertrain / Engine and ECT / Trouble Codes / Pending.
13. Read Pending DTCs.
HINT
If a pending DTC is output, the system is malfunctioning.
14. If the test result is INCOMPLETE or UNKNOWN and no pending DTC is output, perform a universal trip and check for permanent DTCs DTC Check / Clear.
HINT
- If a permanent DTC is output, the system is malfunctioning.
- If no permanent DTC is output, the system is normal.
INSPECTION PROCEDURE
HINT
Read freeze frame data using the Techstream. The ECM records vehicle and driving condition information as freeze frame data the moment a DTC is stored. When troubleshooting, freeze frame data can be helpful in determining whether the vehicle was running or stopped, whether the engine was warmed up or not, whether the air fuel ratio was lean or rich, as well as other data recorded at the time of a malfunction.
PROCEDURE
1. CHECK ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0128)
(a) Connect the Techstream to the DLC3.
(b) Turn the ignition switch to ON.
(c) Turn the Techstream on.
(d) Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.
(e) Read DTCs.
Result:
HINT
If any DTCs other than P0128 are output, troubleshoot those DTCs first.
B -- GO TO DTC CHART Engine Control System - SFI System
A -- Continue to next step.
2. CHECK COOLING SYSTEM
(a) Check for defects in the cooling system that might cause the system to be too cold, such as abnormal radiator fan operation or any modifications.
NG -- REPAIR OR REPLACE COOLING SYSTEM
OK -- Continue to next step.
3. INSPECT THERMOSTAT
(a) Remove the thermostat Removal.
(b) Measure the valve opening temperature of the thermostat.
Standard Value:
80 to 84°C (176 to 183°F)
HINT
In addition to the above check, confirm that the valve is completely closed when the temperature is below the standard.
(c) Reinstall the thermostat Installation.
NG -- REPLACE THERMOSTAT Components
OK -- REPLACE ECM Components