P0128

3UR-FE ENGINE CONTROL: SFI SYSTEM: P0128: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)
P0128 - Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)

CAUTION / NOTICE / HINT

DESCRIPTION

This DTC is stored when the Engine Coolant Temperature (ECT) does not reach 75°C (167°F) despite sufficient engine warm-up time having elapsed.





MONITOR DESCRIPTION





The ECM estimates the ECT based on the starting temperature, engine loads, and engine speeds. The ECM then compares the estimated temperature with the actual ECT. When the estimated ECT reaches 75°C (167°F), the ECM checks the actual ECT. If the actual ECT is below 75°C (167°F), the ECM interprets this as a malfunction in the thermostat or the engine cooling system and stores the DTC.

MONITOR STRATEGY





TYPICAL ENABLING CONDITIONS





TYPICAL MALFUNCTION THRESHOLDS





CONFIRMATION DRIVING PATTERN





1. Stop the engine and allow it to soak.

2. Connect Techstream to the DLC3.

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

4. Clear the DTCs (even if no DTCs are stored, perform the clear DTC operation).

5. Enter the following menu items: Powertrain / Engine and ECT / Data List / All Data / 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. Set the heater to MAX HOT with fresh air mode selected and turn the A/C off.

8. 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 menu: Data List / Function / Snap-shot configuration / Record time / 5 min.
- Data capture can be started by using the target point. For example, setting the target point to an engine speed of 4000 rpm and then revving the engine, etc. to raise the engine speed to a speed of 4000 rpm or more will cause data capture to start.

9. 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
- This DTC relates to the thermostat.
- Read freeze frame data using the Techstream. Freeze frame data records the engine condition when malfunctions are detected. 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.

PROCEDURE

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

(a) Connect the Techstream to the DLC3.

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

(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 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 WATER INLET SUB-ASSEMBLY WITH THERMOSTAT

(a) Remove the water inlet sub-assembly with thermostat Removal.

(b) Measure the valve opening temperature of the water inlet sub-assembly with thermostat.

Standard opening temperature:

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 water inlet sub-assembly with thermostat Installation.

NG -- REPLACE WATER INLET SUB-ASSEMBLY WITH THERMOSTAT Removal

OK -- REPLACE ECM Removal