P0128

1NZ-FXE ENGINE CONTROL SYSTEM: SFI SYSTEM: P0128: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)

DTC P0128 - Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)

DESCRIPTION
HINT: This is the purpose of detecting the "thermostat" malfunction.

If the engine coolant temperature (ECT) does not reach 75°C (167°F) despite sufficient warm-up time has elapsed.






MONITOR DESCRIPTION





The ECM estimates the engine coolant temperature (ECT) based on engine starting temperature, engine loads and engine speed. The ECM then compares the estimated ECT 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 will interpret this as a fault in the thermostat or the engine cooling system and set a DTC.

MONITOR STRATEGY





TYPICAL ENABLING CONDITIONS





TYPICAL MALFUNCTION THRESHOLDS





COMPONENT OPERATING RANGE





MONITOR RESULT

Refer to detailed information Mode 6 Data.

INSPECTION PROCEDURE
HINT: Read freeze frame data using Techstream. 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 Freeze Frame Data.

PROCEDURE

1. CHECK COOLING SYSTEM
(a) Check that there is a defect in the cooling system which causes overcooling, such as abnormal radiator fan operation, modified cooling system and so on.
OK:
There is no modification of cooling system.
NG -- REPAIR OR REPLACE COOLING SYSTEM
OK -- Continue to next step.

2. INSPECT THERMOSTAT
(a) Check the valve opening temperature of the thermostat.
OK:
Thermostat valve begins to open at temperature of 80 to 84°C (176 to 183°F).
HINT: Also check the valve is completely closed at a temperature lower than specified above.

NG -- REPLACE THERMOSTAT
OK -- REPLACE ECM