Hummer H1 (2006+). Manual - part 341

12-40

Electrical System

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12.

Turn the ignition ON leaving the engine OFF.
Reconnect the glow plug relay control harness.
With a DMM connected to ground, back probe
the glow plug relay signal circuit (506 LB) at the
ECM harness connector. Use a scan tool to com-
mand the glow plugs ON. Observe the DMM
while the glow plugs are commanded ON.
Is the voltage at the specified value?

5.0-5.6 Volts

Go to step 21.

Go to step 13.

13.

Turn the ignition OFF. Disconnect the right and
left bank glow plug output circuit connectors at
the glow plug relay. With an unpowered test lamp
connected to B+, probe each circuit.
Does each circuit turn ON the test lamp?

Go to step 26.

Go to step 14.

14.

Turn the ignition OFF. Disconnect each glow plug
connector at the glow plug that did not illuminate
the test lamp. With an unpowered test lamp con-
nected to B+, probe the terminal on the glow
plug.
Does each glow plug illuminate the test lamp?

Go to step 26.

Go to step 25.

15.

Turn the ignition OFF. Disconnect each glow plug
connector at the glow plug. With an unpowered
test lamp connected to B+, probe each circuit at
the glow plug output connectors.
Is the test lamp OFF at each of the circuits?

Go to step 20.

Go to step 27.

16.

Repair an open or a short to ground in the glow
plug relay ignition feed circuit (CKT 239 RD).
Did you complete the repair?

Go to step 30.

17.

Repair any opens or poor connections in the glow
plug relay ground circuit (BK).
Did you complete the repair?

Go to step 30.

18.

Inspect the glow plug relay control circuit (466
YL) for an open or short to ground. If the glow
plug relay control circuit is open or shorted to
ground, repair as necessary.
Did you find and correct the condition?

Go to step 30.

Go to step 19.

19.

Inspect the glow plug relay control circuit (CKT
466 YL) for a proper connection at the ECM and
replace the terminal if necessary.
Did you find an improper connection and make
the necessary repair?

Go to step 30.

Go to step 29.

20.

Inspect the glow plug relay signal circuit (CKT
506 LB) for an open or short to ground. If the
glow plug relay signal circuit is open or shorted
to ground, repair as necessary.
Did you find and correct the condition?

Go to step 30.

Go to step 28.

Glow Plugs Inoperative (Cont’d) (Figure 12-117)

Step

Action

Value

Yes

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Electrical System 12-41

21.

Inspect the glow plug relay signal circuit (CKT
506 LB) for a proper connection at the ECM and
replace the terminal if necessary.
Did you find an improper connection and make
the necessary repair?

Go to step30.

Go to step 22.

22.

Test for a short to voltage in the glow plug relay
signal circuit (CKT 506 LB).
Did you find the improper condition?

Go to step 30.

Go to step 28.

23.

Test for a short to voltage in the glow plug relay
control circuit (CKT 466 YL).
Did you find and correct the condition?

Go to step 30.

Go to step 29.

24.

Repair the open or poor connection on the battery
feed circuit.
Did you complete the repair?

Go to step 30.

25.

Replace any glow plug that did not illuminate the
test lamp.
Did you complete the repair?

Go to step 30.

26.

Repair the open or poor connections in the glow
plug harness.
Did you complete the repair?

Go to step 30.

27.

Repair the short to ground in the glow plug har-
ness.
Did you complete the repair?

Go to step 30.

28.

Replace the glow plug relay.
Did you complete the repair?

Go to step 30.

29.

THE NEW ECM MUST BE PRO-
GRAMMED.Replace the ECM.
Did you complete the repair?

Go to step 30.

30.

Use a scan tool to clear the DTC’s. Start the
engine. Allow the engine to idle until the engine
reaches normal operating temperature. Select the
DTC and the specific DTC function. Enter the
DTC number which was set. Operate the vehicle,
with the Conditions for Setting this DTC, until the
scan tool indicates the diagnostic Ran.
Does the scan tool indicate the diagnostic Passed?

Go to step 31.

Go to step 2.

31.

Does the scan tool display any addition undiag-
nosed DTC’s?

Go to the appli-

cable DTC

table.

System OK.

Glow Plugs Inoperative (Cont’d) (Figure 12-117)

Step

Action

Value

Yes

12-42

Electrical System

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Fuel Tank Selector System Inoperative (No Tank Switch) (Figure 12-114)

Step

Action

Value(s)

Yes

Remove fuel tank selector switch from dash, and
disconnect switch from harness. Using a DVOM,
set to measure resistance, probe the black wire of
the fuel selector switch connector (CKT 59) with
the black lead, and the positive lead on the ground
studs at left of dash.Is resistance below specifica-
tion?

<.2

Go to step 4

Repair open or
bad connection
in CKT 59
between fuel
selector switch
and IP ground
studs.

Using a DVOM set to measure voltage, place the
positive lead on the grey wire (CKT 787) at the
fuel tank selector switch. Turn the ignition ON.
Does the meter read voltage?

+12 v

Go to step 3

Repair open or
short to ground
in CKT 787.

Re-connect fuel tank selector switch. Using a
DVOM, set to measure voltage, back probe the
red wire (CKT 786) with the negative lead and
brown wire (CKT 789) with the positive lead.
Turn the ignition ON. With the switch in the AUX
position voltage should be present, when the
switch is moved to the MAIN position, reverse
polarity voltage should be present. Does meter
show opposite voltages when moved between
AUX and MAIN?

+12 v= AUX

-12 v=MAIN

Go to step 4.

Replace fuel
tank selector
switch and
recheck system.

Disconnect fuel selector valve electrical connec-
tion. Using a DVOM, set to measure voltage,
probe the brown wire with the positive lead, and
the red lead with the negative lead. Turn the igni-
tion ON. With the switch in the AUX position
voltage should be present, when the switch is
moved to the MAIN position, reverse polarity
voltage should be present. Does meter show
opposite voltages when moved between AUX and
MAIN

12 v+=AUX

12 v-=MAIN

Replace fuel
selector valve

Go to step 5.

Relocate the ground lead of the DVOM, set to
measure voltage to a known good ground. Turn
the ignition ON, and the tank selector switch in
the AUX position, probe the brown wire (CKT
789) with the positive meter lead.
Is voltage present?

+12 v

Go to step 8.

Repair open,
bad connection
or short to
ground in CKT
789.

Turn the ignition ON, and the tank selector switch
in the MAIN position, probe the red wire (CKT
786) with the positive meter lead, the ground lead
should be on a know good ground.
Is voltage present?

+12 v

No electrical
problems found,
problem may be
intermittent or
mechanical.

Repair open,
bad connection
or short to
ground in CKT
786.

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Electrical System 12-43

IGNITION SYSTEM

System Description

The ignition switch is located on the steering column just below the ignition lock cylinder (Figure 12-34). The ignition switch bolts
to the lock cylinder housing and is controlled by the column lock actuator. When the ignition lock cylinder is rotated forward it
pushes the lock actuator down. The downward action of the actuator is transferred to the ignition switch causing the switch to se-
lect a different status (“Off”, “Run”, “Start”). When the lock cylinder is released after a full forward motion it will default to the
“Run” position. When the ignition lock cylinder is rotated backwards it pulls the lock actuator up. The upward action of the actua-
tor is again transferred to the ignition switch causing the switch to select a different status (“Start”, “Run”, “Off” “Lock” “Acces-
sory”).

Figure 12-34: Ignition Switch Exploded View

HORN BRUSH

IGNITION INTERLOCK SOLENOID

IGNITION INTERLOCK

CABLE

IGNITION

LOCK CYLINDER

CONTACT

TURN SIGNAL SWITCH

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