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HEST Indicator (High Exhaust System Temperature). An instrument panel indicator
which appears when the exhaust temperature is unusually high due to recent regen-
eration. This is normal behavior of the aftertreatment system, intended to notify the
driver and technician that the exhaust system temperature is high and that caution
should be observed around the exhaust system.
DPF Indicator. An instrument panel indicator which displays when particulate ac-
cumulation has reached a preset level in the DPF, and regeneration is needed. The
bus should either be operated with a more demanding duty cycle until the indicator
goes off, or it should be scheduled for a Stationary Regeneration at a service facility.
Levels of Notification
Regeneration—the process which burns off soot accumulation in the DPF—occurs
automatically as the bus is operated, as long as certain operating conditions (such as
minimum speed thresholds) are met. When bus operating conditions do not provide
adequate opportunity for the regeneration system to keep the DPF clear, soot begins
to accumulate. A system of driver alerts keeps the driver informed when the exhaust
system is in need of regeneration, and of high exhaust temperature associated with
regeneration. Several levels of regeneration alerts occur in sequence, each indicating
a more imperative warning.
High Exhaust Temperature Notification
The High Exhaust System Temperature (HEST) indicator appears to alert the driver
when exhaust temperature is unusually high and that prudent judgement should be
applied regarding the proximity of people or combustibles to the exhaust system.
For example, the bus should not be parked on a surface of grass or weeds.
With the Cummins engine, the HEST indicator appears whenever the exhaust
temperature is high (752°F or above), regardless of moving speed.
The driver should be familiar with and abide by all instructions, warnings, and
cautions in the engine manufacturer's operator's manual regarding safe operation
when the HEST indicator is on.
• The HEST alert appears in the instrument panel.
• The audible alarm sounds one beep.
ROUTINE OPERATION
HEST Notification
The HEST alert appears in the instrument
panel' s warning bank.
The audible alert
sounds one beep.
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