Jeep Cherokee 2000 Service Manual - page 1257
cycle. This is on a cold or cool engine. After heating,
the current draw will drop to approximately 9–12
amps per plug.
Total momentary current draw for all four plugs is
approximately 100 amps on a cold engine dropping to
a total of approximately 40 amps after the plugs are
heated.
Electrical operation of the glow plugs are con-
trolled by the glow plug relay. Refer to the previous
Glow Plug Relay—ECM Output for additional infor-
mation.
ELECTRIC VACUUM MODULATOR (EVM)—ECM
OUTPUT
DESCRIPTION
This circuit controls operation of the Electric Vac-
uum Modulator (EVM). The EVM controls operation
of the EGR valve.
Refer to Group 25, Emission Control System for
information. See Electric Vacuum Modulator.
DIAGNOSIS AND TESTING
DIESEL DIAGNOSTICS
The ECM controllers perform engine off diagnostic
tests, which may be heard for about 60 seconds after
turning the key off.
ASD RELAY TEST
To perform a test of the relay and its related cir-
cuitry, refer to the DRB scan tool. To test the relay
only, refer to Relays—Operation/Testing in this sec-
tion of the group.
Diagnostic Trouble Codes: Refer to On-Board
Diagnostics in Group 25, Emission Control System
for a list of Diagnostic Trouble Codes (DTC’s) for cer-
tain fuel system components.
ENGINE SPEED SENSOR TEST
To perform a test of the engine speed sensor and
its related circuitry, refer to the 3.1L Powertrain
Diagnostic Procedures Manual.
Diagnostic Trouble Codes: Refer to On-Board
Diagnostics in Group 25, Emission Control System
for a list of Diagnostic Trouble Codes (DTC’s) for cer-
tain fuel system components.
ENGINE COOLANT TEMPERATURE SENSOR
TEST
The sensor is located on the side of cylinder head
near the rear of fuel injection pump (Fig. 15).
For a list of Diagnostic Trouble Codes (DTC’s) for
certain fuel system components, refer to On-Board
Diagnostics in Group 25, Emission Control System.
To test the sensor only, refer to the following:
(1) Disconnect wire harness connector from coolant
temperature sensor.
(2) Test the resistance of the sensor with a high
input impedance (digital) volt–ohmmeter. The resis-
tance (as measured across the sensor terminals)
should be less than 1340 ohms with the engine
warm. Refer to the following Sensor Resistance
(OHMS) chart. Replace the sensor if it is not within
the range of resistance specified in the chart.
(3) Test continuity of the wire harness. Do this
between the ECM wire harness connector and the
sensor connector terminal. Also test continuity of
wire harness to the sensor connector terminal. Refer
to Group 8W for wiring connector and circuitry infor-
mation. Repair the wire harness if an open circuit is
indicated.
(4) After tests are completed, connect electrical
connector to sensor.
GLOW PLUG TEST
Hard starting or a rough idle after starting may be
caused by one or more defective glow plugs. Before
testing the glow plugs, a test of the glow plug relays
should be performed. This will ensure that 12V+ is
available at the plugs when starting the engine.
Refer to the Glow Plug Relay Test for information.
For accurate test results, the glow plugs should be
removed from the engine. The plugs must be checked
Fig. 15 Engine Coolant Temperature Sensor
Location
1 – PCM ENGINE COOLANT TEMPERATURE (ECT) SENSOR
2 – ECM ENGINE COOLANT TEMPERATURE (ECT) SENSOR
3 – ECM ECT SENSOR HARNESS CONNECTOR
4 – PCM ECT SENSOR HARNESS CONNECTOR
XJ
FUEL SYSTEM—2.5L DIESEL ENGINE
14 - 31
DESCRIPTION AND OPERATION (Continued)