SECTION 3 - CHASSIS & TURNTABLE
3120740
– JLG Lift –
3-95
ENGINE COOLANT TEMPERATURE (ECT) SENSOR
The engine coolant temperature (ECT) sensor is a g thermistor
(a resistor which changes value based on temperature)
mounted in the engine coolant stream. Low coolant tempera-
ture 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 ECM supplies a 5-volt signal to the ECT sen-
sor through resistors in the ECM 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
ECM calculates the engine coolant temperature. Engine cool-
ant temperature affects most of the systems that the ECM con-
trols.
After engine start-up, the temperature should rise steadily to
about 85°C (185°F). it then stabilizes when the thermostat
opens. If the engine has not been run for several hours (over-
night), the engine coolant temperature and intake air tem-
perature 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 memory
(EEPROM) is a permanent memory chip that is located within
the ECM. The EEPROM contains the pro-gram and the calibra-
tion information that the ECM needs to control engine opera-
tions.
If the ECM is replaced, the new ECM will need to be pro-
grammed. An IBM-compatible computer and software con-
taining the correct program and calibration for the application
are required to program the ECM.
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-com-
patible computer with diagnostic software. By monitoring the
voltage out-put of the oxygen sensor, the ECM 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 seconds
will set OTC 32. A constant voltage above 650 mV for 10 con-
secutive seconds will set OTC 42.
When installing a new oxygen sensor, tighten to a torque of
29.5 to 40 ft. lbs. (40 to 54 Nm).
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