Hummer H1 Service Manual page 150

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Low Temperature—High Resistance Test
1. Connect scan tool and start engine.
2. Note indicated temperature:
• If temperature is normal, problem is with sensor wires
and connections.
• If temperature is at or above 266° F (130° C), continue
with test. Disconnect sensor wires and note scan tool
reading:
• If temperature now reads -22° F (-30° C), sensor has
failed.
• If temperature is OK, problem is faulty sensor ground,
reference wire shorted to ground, or PCM has fault.
Figure 3-11: Coolant Temperature Sensor Circuit
Baro Sensor
The baro sensor on turbo diesel models is used to send a baro-
metric pressure signal to the PCM. The signal is in the form of
a voltage that is interpreted by the PCM. The sensor signal is to
adjust fuel metering and timing at different altitudes. The scan
tool is used for baro sensor testing.
Engine Shut-Off Solenoid Test
A shut-off solenoid failure can result in run-on, or a no start
condition. The failure may be with the solenoid, or with the re-
lated wiring (Figure 3-12).
1. Connect the scan tool.
2. Select Miscellaneous Tests, Engine Outputs, Injection
Pump, then Engine Shutoff.
3. Use the arrow keys to toggle the solenoid Off/On and
listen for the solenoid to activate or click.
5745159
COOLANT
TEMPERATURE
SENSOR
PCM
Fuel, Emissions, and Exhaust
4. If the solenoid does not activate, perform wiring tests with
a DVOM (Figure 3-12).
5. If the wiring tests OK, replace the solenoid.
ENGINE
SHUTOFF SOLENOID
F/SOL
TO IGNITION
SWITCH
20 AMP
Figure 3-12: Engine Shut-Off Solenoid Circuit
Engine Shut-Off Solenoid Replacement
Removal
1. Disconnect the electrical connector from the ESO solenoid
(Figure 3-13).
NOTE: Remove any debris from the ESO mounting surface
on the injection pump before servicing the ESO solenoid. This
will prevent contaminants from getting into and damaging the
injection pump.
2. Remove the solenoid (style may vary) and O-ring from the
injection pump housing.
ESO
SOLENOID
Figure 3-13: ESO Solenoid Replacement
3-13
PCM
TO
FUEL
SOLENOID
DRIVER
SOLENOID
CONTROL
TO HARNESS
CONNECTION
INJECTION
PUMP