A system for diagnosing operation of a cooling system for an internal combustion
engine includes a coolant temperature sensor producing a temperature signal corresponding
to coolant fluid temperature, means for determining either an engine load or a
throttle percentage, and a control computer configured to diagnose operation of
the cooling system as a function of the temperature signal, either the engine load
or throttle percentage, and a fuel delivery command for controllably supplying
fuel to the engine. After expiration of a diagnostic period, the control computer
diagnoses the cooling system as normally operating if the diagnostic period ended
by the temperature signal meeting or exceeding a predefined temperature and if
a total energy used by the engine during the diagnostic period is less than an
estimated energy, and diagnoses the cooling system as failing if the total energy
used during the diagnostic period otherwise meets or exceeds the estimated energy.
