DIAGNOSTIC MANUAL
Horsepower (hp)
Horsepower is the unit of work done in a given period of time, equal to 33,000 pounds multiplied by one
foot per minute. 1 hp = 33,000 lb x 1 ft. /1 min.
Humidity Sensor (HS)
A sensor that measures the moisture content of filtered air entering the intake system.
Hydrocarbons
Organic compounds consisting of hydrogen and carbon (fuel and oil).
Hydrocarbon slip
A normal condition that occurs in the exhaust stream in high idle time applications, where diesel fuel does
not fully combust in the aftertreatment system during regeneration. The diesel fuel “slips” through the Diesel
Particulate Filter (DPF), and into the clean side of the exhaust.
Injection Pressure Regulator
(IPR) valve
A valve that is used to maintain desired injection control pressure.
Injection Control Pressure (ICP)
sensor
Provides a feedback signal to the ECM indicating injection control pressure.
Inlet Air Heater (IAH)
The IAH is primarily used to assist in starting the engine during cold weather. In addition, it helps to reduce
white smoke emissions by heating the incoming air.
Inlet Air Heater Fuel Igniter
(IAHFI)
The IAHFI heats the intake air by vaporizing and igniting fuel in the air inlet duct.
Inlet Air Heater Fuel Solenoid
(IAHFS)
As the engine is cranked, the ECM energizes the IAHFS valve, introducing fuel into the IAHFI, which ignites
and warms the air being drawn into the engine.
Inlet Air Heater Relay (IAHR)
The IAHR provides voltage to the IAHFI, and is controlled by the ECM.
Inlet Air Temperature (IAT)
sensor
A thermistor sensor that monitors intake air temperature.
Intake manifold
Engine component that evenly supplies air to each intake port in the cylinder head(s).
Intake Manifold Pressure (IMP)
sensor
A variable capacitance sensor used to indicate air pressure in the intake manifold.
Intake Manifold Temperature
(IMT) sensor
A thermistor sensor used to indicate air temperature in the intake manifold.
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