JLG 740A, Service And Maintenance Manual

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SECTION 3 - CHASSIS & TURNTABLE
3-100 – JLG Lift – 3121160
ELECTRICALLY ERASABLE PROGRAMMABLE
READ ONLY MEMORY (EEPROM)
The electrically erasable programmable read only mem-
ory (EEPROM) is a permanent memory chip that is
located within the Engine Module. The EEPROM contains
the pro-gram and the calibration information that the
Engine Module needs to control engine operations.
If the Engine Module is replaced, the new Engine Module
will need to be programmed. An IBM-compatible com-
puter and software containing the correct program and
calibration for the application are required to program the
Engine Module.
HEATED OXYGEN SENSOR
The heated oxygen sensor is mounted in the exhaust
stream where it can monitor the oxygen content of the
exhaust gas. The oxygen present in the exhaust gas
reacts with the sensor to produce a voltage output. This
voltage should constantly fluctuate from approximately
100 mV to 900 mV. The heated oxygen sensor voltage can
be monitored on an IBM PC-compatible computer with
diagnostic software. By monitoring the voltage out-put of
the oxygen sensor, the Engine Module calculates the
pulse width command for the injectors to produce the
proper combustion chamber mixture.
Low HO2S voltage indicates a lean mixture which will
result in a rich command to compensate.
High HO2S voltage indicates a rich mixture which will
result in a lean command to compensate.
A constant voltage below 200 mV for 10 consecutive sec-
onds will set OTC 32. A constant voltage above 650 mV
for 10 consecutive seconds will set OTC 42.
INTAKE AIR TEMPERATURE (IAT) SENSOR
The intake air temperature (IAT) sensor is a thermistor
which changes its resistance based on the temperature of
air entering the engine. Low temperature produces a high
resistance of 100,000 ohms at -40°C (-40°F). High temper-
ature causes a low resistance of 70 ohms at 130°C
(266°F). The Engine Module supplies a 5-volt signal to the
sensor through a resistor in the Engine Module and moni-
tors the signal voltage. The signal voltage will be high
when the incoming air is cold and low when the incoming
air is hot. By measuring the voltage, the Engine Module
calculates the incoming air temperature. The IAT sensor
signal is used to adjust spark timing according to the
incoming air density. An IBM PC-compatible computer
with diagnostic soft-ware can be used to display the tem-
perature of the air entering the engine. The temperature
should read close to the ambient air temperature when
the engine is cold, and rise as engine compartment tem-
perature increases. If the engine has not been run for sev-
eral hours (overnight), the IAT sensor temperature and
engine coolant temperature should read close to each
other. A failure in the IAT sensor circuit will set DTC 35 or
DTC 45.