JLG 601S ANSI Service Manual - Manual (Page 118)

SECTION 3 - CHASSIS & TURNTABLE
3-78 – JLG Lift – 3120746
ENGINE COOLANT TEMPERATURE (ECT)
SENSOR
The engine coolant temperature (ECT) sensor is a g
thermistor (a resistor which changes value based on tem-
perature) mounted in the engine coolant stream. Low cool-
ant temperature produces a high resistance of 100,000
ohms at -40°C (-40°F). High temperature causes a low
resistance of 70 ohms at 130°C (266°F). The Engine Mod-
ule supplies a 5-volt signal to the ECT sensor through
resistors in the Engine Module and measures the voltage.
The signal voltage will be high when the engine is cold and
low when the engine is hot. By measuring the voltage, the
Engine Module calculates the engine coolant temperature.
Engine coolant temperature affects most of the systems
that the Engine Module controls.
After engine start-up, the temperature should rise steadily
to about 85°C (185°F). it then stabilizes when the thermo-
stat opens. If the engine has not been run for several
hours (overnight), the engine coolant temperature and
intake air temperature displays should be close to each
other. A fault in the engine coolant sensor circuit will set
DTC 33 or DTC 43.
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.