Toyota Sienna Service Manual: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)
HINT:
This DTC relates to the thermostat.
DESCRIPTION
This DTC is set when the Engine Coolant Temperature (ECT) does not reach 75°C (167°F) despite sufficient engine warm-up time.
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 sets the DTC.
MONITOR STRATEGY
TYPICAL ENABLING CONDITIONS
TYPICAL MALFUNCTION THRESHOLDS
INSPECTION PROCEDURE
HINT:
Read freeze frame data using the intelligent tester. 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.
1 CHECK ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0128)
(a) Connect the intelligent tester to the DLC3.
(b) Turn the ignition switch to the ON position.
(c) Turn the tester on.
(d) Select the following menu items: DIAGNOSIS / ENHANCED OBD II / DTC INFO / CURRENT CODES.
(e) Read the DTCs.
Result 
HINT: If any DTCs other than P0128 are output, troubleshoot those DTCs first.
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.
3 INSPECT THERMOSTAT
(a) Remove the thermostat (See page CO-16).
(b) Check the valve opening temperature of the thermostat (See page CO-17).
Standard: 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 (See page CO-17).
REPLACE ECM (See page ES-498)
Insufficient Coolant Temperature for Closed Loop Fuel Control
DESCRIPTION
Refer to DTC P0115 (See page ES-133).
MONITOR DESCRIPTION
The resistance of the ECT sensor varies in proportion to the actual ECT. The
ECM supplies a constant
voltage to the ...
Oxygen Sensor Circuit
HINT:
Sensor 2 refers to the sensor mounted behind the Three-Way Catalytic
Converter (TWC) and located far
from the engine assembly.
DESCRIPTION
A three-way catalytic converter (TWC) is used ...
Other materials:
On-vehicle inspection
1. INSPECT BRAKE BOOSTER
(a) Air tightness check.
(1) Start the engine and stop it after 1 or 2 minutes.
Depress the brake pedal several times slowly.
HINT:
If the pedal goes down farthest at the 1st time,
and gradually rises at the 2nd or 3rd time, the
booster is airtight.
(2) Depre ...
Before driving
Floor mat
Use only floor mats designed specifically for vehicles of the same
model and model year as your vehicle. Fix them securely in place
onto the carpet.
Insert the retaining hooks (clips)
into the floor mat eyelets.
Turn the upper knob of each
retaining hook (clip) to secu ...
Cruise Main Indicator Light Circuit
DESCRIPTION
When the cruise control main switch is on, the CRUISE main indicator light
and READY indicator light
come on. This indicates the control condition (presence or absence of a vehicle
in front, vehicle-to-vehicle
distance, and set vehicle speed) and fail-safe state through the multip ...
