P0128

2ZR-FE ENGINE CONTROL SYSTEM: SFI SYSTEM: P0128: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)
P0128 - Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)

DESCRIPTION

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

HINT
This DTC relates to the thermostat.





MONITOR DESCRIPTION





The ECM estimates the Engine Coolant Temperature (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 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





- Stop the engine and allow it to soak.

- Connect the Techstream to the DLC3.

- Turn the ignition switch to ON and turn the Techstream on [A].

- Enter the following menu items: Powertrain / Engine and ECT / Data List / All Data / Coolant Temp and Intake Air.

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

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

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

HINT
- Data can be captured relatively easily by using the snapshot function in the Data List.
- Enter the following menu: Data List / Function / Snapshot configuration / Record time / 5 min.
- Data capture can be started by using the target point function. 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.
- After "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. 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 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 Removal

OK -- REPLACE ECM Removal