DSG-423 ENGINE CONTROLS
08-6
Cylinder Head Temperature (CHT) Sensor
The Cylinder Head Temperature (CHT) Sensor is a
thermistor which changes its resistance based on the
temperature of cylinder head. Low 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 GCP supplies a 5 volt
signal to the sensor through a resistor in the GCP and
monitors the signal voltage. The signal voltage will be
high when the cylinder head is cold and low when the
cylinder head is hot. By measuring the voltage, the GCP
calculates the cylinder head temperature. The CHT
sensor signal is used to adjust spark timing according to
the incoming air density.
Heated Oxygen Sensor (HO2S)
The Heated Oxygen Sensor (HO2S) 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 100mV to 900 mV, when the engine is
running in closed loop fuel control.
The Heated Oxygen Sensor (HO2S) voltage can be
monitored on an IBM PC compatible computer with
diagnostic software. By monitoring the voltage output of
the oxygen sensor, the GCP calculates the pulse width
command for the injectors to produce the proper
combustion chamber mixture.
The 4-wire HO2S indicates whether the air/fuel ratio is
rich or lean with respect to stoichiometry. The signal
from this sensor contains valid air/fuel ratio information
only when the sensor element has reached its normal
operating temperature. The 4-wire HO2S also has an
isolated case ground which goes to Signal Return
(SIGRTN) either in the processor (as a dedicated HO2S
ground) or as a jumper to SIGRTN in the wiring
harness.
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.
Specifications
• Accuracy of measurement: ±1.5%
• Operating Temp. Range: 350°C to 850°C (sensor
tip)
• Sensor Response Time: 300-1500 msec.
• Heater Current Draw: 1 A steady state
• Voltage Output:
0 - 450 mV (lean exhaust gas)
450 - 1000 mV (rich exhaust gas)
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