Toyota Tundra Service Manual: Thermostat (P0128)

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 less than 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 the Techstream to the DLC3.
3. Turn the ignition switch to ON and turn the Techstream on [A].
4. Enter the following menu items: Powertrain / Engine and ECT / Data List / Coolant Temp and Intake Air.
5. Check that "Coolant Temp" is 56°C (133°F) or less and "Intake Air" is between 0 and 35°C (0 and 95°F).
6. Set the heater to MAX HOT with fresh air mode selected and turn the A/C off.
7. 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 function. For example, setting the target point to an engine speed of 4000 rpm and then racing the engine, etc. to raise the engine speed to a speed of 4000 rpm or more will cause data capture to start.
8. 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.

CAUTION / NOTICE / HINT

HINT:

• 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 ECM and the engine coolant temperature sensor first.
• 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

(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.

HINT:

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

B

GO TO DTC CHART

A

(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

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

(b) Measure the valve opening temperature of the 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.

NG

REPLACE WATER INLET WITH THERMOSTAT SUB-ASSEMBLY

OK

(a) Inspect the engine coolant temperature sensor (See page ).

OK

REPLACE ECM

NG

REPLACE ENGINE COOLANT TEMPERATURE SENSOR