Toyota Corolla (E120) 2002–2008 Repair Manual / Diagnostics / Sfi system / Coolant thermostat (coolant temperature below thermostat regulating temperature) / Circuit description

Toyota Corolla (E120): Circuit description

If the engine coolant temperature (ect) does not reach 75°c (167°f) despite sufficient warm – up time has elapsed.

Dtc no	Dtc detection condition	Trouble area
P0128	Condition (a), (b) and (c):  cold start  after engine is warmed up  engine coolant temperature is less than 75°c (167°f)	Thermostat cooling system engine coolant temperature sensor ecm

Monitor description

The ecm estimates the engine coolant temperature (ect) based on starting temperature, engine loads, and engine speeds. 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 engine cooling system or thermostat and set a dtc.

Monitor strategy

Typical enabling conditions

Typical malfunction thresholds

Component operating range

Monitor result (mode 06 data)

Refer to page 05–27 for the detailed information on checking monitor status.