P0128: Thermostat: Coolant Temperature Doesn't Reach Warmed-Up Temp.; Dtc: P0128 - Hino Motors HINO 155 series Workshop Manual

Table of Contents

P0128: Thermostat - The coolant temperature does not reach a warmed-up temperature

Technical description

• The thermostat prevents coolant from flowing into the radiator when the engine coolant temperature is less than

76.5 C {169.7 F}, in order to secure the engine warm up function. When the temperature rises above 76.5 C

{169.7 F}, the valve opens and allows coolant to flow into the radiator, thereby preventing the engine from over-

• If the thermostat fails and the valve stays open, it is difficult for the engine coolant temperature to rise, so the

exhaust components that work after the engine coolant temperature has reached a certain value (warm up) will not

operate for a long time. The thermostat must therefore be diagnosed to see if it is working properly.

• In order to detect a malfunction of the thermostat, the above failure is determined when the actual engine coolant

temperature is a certain amount lower than the predicted temperature.

DTC set condition

DTC detection condition

• Engine speed ≥ 700 r/min

• Engine coolant temperature at engine start-up ≤ 52 C {125.6 F}.

• Engine coolant temperature is 76 C {168.8 F} or more after running the engine for 60 seconds or more.

Judgement criteria

• The condition that the actual engine coolant temperature is less than 65 C {149 F} remains for 5 seconds or

Reset condition

• After restoration to normal condition.

Indication, warning or system control regulation when the DTC is set.

• SVS light: OFF

ENGINE (J05E)/TROUBLESHOOTING

Engine coolant

temperature sensor

Coolant temperature sensor

EN01H02127030602016049

SHTS021270300255

Show Quick Links

Table of Contents

Troubleshooting