Oil Pressure Sensor-Pcm Input; Power Grounds; Power Steering Pressure Switch-Pcm Input - Jeep cherokee 2000 Service Manual

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DESCRIPTION AND OPERATION (Continued)
The range of voltage output from the sensor is usu-
ally between 4.6 volts at sea level to as low as 0.3
volts at 26 in. of Hg. Barometric pressure is the pres-
sure exerted by the atmosphere upon an object. At
sea level on a standard day, no storm, barometric
pressure is approximately 29.92 in Hg. For every 100
feet of altitude, barometric pressure drops.10 in. Hg.
If a storm goes through it can change barometric
pressure from what should be present for that alti-
tude. You should know what the average pressure
and corresponding barometric pressure is for your
area.
OIL PRESSURE SENSOR—PCM INPUT
DESCRIPTION
The 3–wire, solid-state engine oil pressure sensor
(sending unit) is located in an engine oil pressure
gallery.
OPERATION
The oil pressure sensor uses three circuits. They
are:
• A 5–volt power supply from the Powertrain Con-
trol Module (PCM)
• A sensor ground through the PCM's sensor
return
• A signal to the PCM relating to engine oil pres-
sure
The oil pressure sensor has a 3–wire electrical
function very much like the Manifold Absolute Pres-
sure (MAP) sensor. Meaning different pressures
relate to different output voltages.
A 5–volt supply is sent to the sensor from the PCM
to power up the sensor. The sensor returns a voltage
signal back to the PCM relating to engine oil pres-
sure. This signal is then transferred (bussed) to the
instrument panel on either a CCD or PCI bus circuit
(depending on vehicle line) to operate the oil pressure
gauge and the check gauges lamp. Ground for the
sensor is provided by the PCM through a low-noise
sensor return.

POWER GROUNDS

OPERATION
The Powertrain Control Module (PCM) has 2 main
grounds. Both of these grounds are referred to as
power grounds. All of the high-current, noisy, electri-
cal devices are connected to these grounds as well as
all of the sensor returns. The sensor return comes
into the sensor return circuit, passes through noise
suppression, and is then connected to the power
ground.
The power ground is used to control ground cir-
cuits for the following PCM loads:
• Generator field winding
• Fuel injectors
• Ignition coil(s)
• Certain relays/solenoids
• Certain sensors
POWER STEERING PRESSURE SWITCH—PCM
INPUT
DESCRIPTION
A pressure sensing switch (Fig. 2) is included in
the power steering system (mounted on the high-
pressure line). This switch will be used only on vehi-
cles equipped with a 2.5L engine and power steering.
Fig. 2 Power Steering Pump Pressure Switch—2.5L
1 – POWER STEERING PRESSURE SWITCH
2 – ELECTRICAL CONNECTOR
3 – POWER STEERING PUMP
OPERATION
The power steering pressure switch provides an
input to the Powertrain Control Module (PCM). This
input is provided during periods of high pump load
and low engine rpm; such as during parking maneu-
vers. The PCM will then increase the idle speed
through the Idle Air Control (IAC) motor. This is
done to prevent the engine from stalling under the
increased load.
When steering pump pressure exceeds 3275 kPa
690 kPa (475 psi
switch will open and the PCM will increase the
engine idle speed. This will prevent the engine from
stalling.
FUEL SYSTEM
Engine
100 psi), the normally closed
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