P0128

2AZ-FXE 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 hybrid vehicle control ECU estimates the engine coolant temperature based on the starting temperature, engine load, and engine speeds. The hybrid vehicle control ECU then compares the estimated temperature with the actual engine coolant temperature. When the estimated engine coolant temperature reaches 75°C (167°F), the hybrid vehicle control ECU checks the actual engine coolant temperature. If the actual engine coolant temperature is less than 75°C (167°F), the hybrid vehicle control ECU interprets this as a malfunction in the water inlet with thermostat sub-assembly or the engine cooling system and sets the DTC.

MONITOR STRATEGY





TYPICAL ENABLING CONDITIONS





TYPICAL MALFUNCTION THRESHOLDS





CONFIRMATION DRIVING PATTERN





1. Stop the engine and allow it to soak.

2. Connect the Techstream to the DLC3.

3. Turn the power switch on (IG) and turn the Techstream on [A].

4. Clear the DTCs (even if no DTCs are stored, perform the clear DTC procedure) Reading and Clearing Diagnostic Trouble Codes.

5. Enter the following menus: Powertrain / Engine and ECT / Data List / Primary / Coolant Temp and Intake Air.

6. Check if "Coolant Temp" is 56°C (133°F) or less and "Intake Air" is between 0 and 35°C (32 and 95°F).

7. Put the engine in inspection mode (maintenance mode) Component Tests and General Diagnostics.

8. Set the heater to MAX HOT with fresh air mode selected and turn the A/C off.

9. Start the engine and drive the vehicle at 80 km/h (50 mph) for 15 minutes [B].

CAUTION:
When performing the confirmation driving pattern, obey all speed limits and traffic laws.

HINT
- Data can be captured relatively easily by using the snapshot function in the Data List.
- Enter the following menus: Data List / Function / Snapshot Configure / Duration / 5 min.
- Data capture can be started by using the target point. For example, setting the target point to an accelerator position of 90% and then racing the engine, etc. to depress the accelerator pedal for accelerator position of 90% or more will cause data capture to start.

10. After driving the vehicle at 80 km/h (50 mph) and "Coolant Temp" stabilizes, check that "Coolant Temp" is 75°C (167°F) or higher [C].

HINT
If "Coolant Temp" is below 75°C (167°F) while driving the vehicle at 80 km/h (50 mph), inspect the cooling system and thermostat.

INSPECTION PROCEDURE

HINT
- Read freeze frame data using the Techstream. The hybrid vehicle control ECU records vehicle and driving condition information as freeze frame data the moment a DTC is stored. When troubleshooting, freeze frame data can help determine if the vehicle was moving or stationary, if the engine was warmed up or not, if the air fuel ratio was lean or rich, and other data from the time the malfunction occurred.
- When the DTC is output, check the engine coolant temperature using the Techstream. Enter the following menus: Powertrain / Engine and ECT / Data List / Coolant Temp. If the Coolant Temp value is lower than the actual engine coolant temperature, the engine coolant temperature sensor circuit may be malfunctioning. In this case, check the wire harnesses and connectors (and those connections) between the hybrid vehicle control ECU and the engine coolant temperature sensor first.

PROCEDURE

1. CHECK ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0128)

(a) Connect the Techstream to the DLC3.

(b) Turn the power switch on (IG).

(c) Turn the Techstream on.

(d) Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.

(e) Read the DTCs.

Result:





HINT
If any DTCs other than P0128 are output, troubleshoot those DTCs first.

B -- GO TO DTC CHART 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 Removal

OK -- REPLACE HYBRID VEHICLE CONTROL ECU Removal