JLG 450A_AJ Series II Service Manual - Manual (Page 148)

SECTION 3 - CHASSIS & TURNTABLE
3-98 – JLG Lift – 3121180
ENGINE COOLANT TEMPERATURE (ECT) SENSOR
The Engine Coolant Temperature (ECT) sensor is a therm-
istor (a resistor which changes value based on tempera-
ture) mounted in the engine coolant stream. Low coolant
temperature produces a high resistance of 100,000 ohms
at -40°C (-40°F). High temperature causes a low resis-
tance of 70 ohms at 130°C (266°F). The ECM supplies a
5-volt signal to the ECT sensor 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 coolant temperature
affects most of the systems that the ECM controls.
After engine start-up, temperature should rise steadily to
about 85°C (185°F), then stabilize when the thermostat
opens. If engine has not been run for several hours (over-
night), engine coolant temperature and intake air tempera-
ture displays should be close to each other. A fault in the
engine coolant sensor circuit sets 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 located within
the ECM. The EEPROM contains program and calibration
information needed to control engine operations. If
replaced, the new ECM must be programmed. An IBM-
compatible computer and software containing 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 to monitor exhaust gas oxygen content. Oxygen in
the exhaust gas reacts with the sensor to produce a volt-
age output. This voltage should constantly fluctuate from
approximately 100 mV to 900 mV. Heated oxygen sensor
voltage can be monitored on an IBM PC-compatible com-
puter with diagnostic software. By monitoring oxygen sen-
sor voltage output, the ECM calculates the pulse width
command for injectors to produce proper combustion
chamber mixture.
Low HO2S voltage indicates a lean mixture which results
in a rich command to compensate.
High HO2S voltage indicates a rich mixture which results
in a lean command to compensate.
A constant voltage below 200 mV for 10 consecutive sec-
onds sets OTC 32. A constant voltage above 650 mV for
10 consecutive seconds sets OTC 42.