Hummer H1 Service Manual page 818

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Fuel Tank Selector System Inoperative (No Tank Switch)
Step
1 Important: Before clearing the DTC's use the
scan tool Capture Info in order to record the
Freeze Frame and the failure records for refer-
ence, as the data will be lost when the clear func-
tion is used.
Was the On-Board Diagnostic (OBD) System
Check performed?
2 Turn the ignition OFF for 10 seconds. Turn the
ignition ON. Does the fuel pump operate during
the glow plug cycle?
3 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?
4 Using a DVOM set to measure voltage, place the
ground lead on the negative studs to right of the
IP panel. Place the positive lead on the grey wire
(CKT 787) at the fuel tank selector switch. Turn
the ignition OFF for 10 seconds. Turn the ignition
ON. Does the meter read voltage?
5 Re-connect fuel tank selector switch. Using a
DVOM set to measure voltage, backprobe the red
wire (CKT 786) with the negative lead and brown
wire (CKT 789) with the positive lead.Turn the
ignition OFF for 10 seconds. 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. If fuel pump shuts off during
test, repeat cycle of key. Does meter show oppo-
site voltages when moved between AUX and
MAIN
6 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 OFF for 10 seconds. 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
05745159
Action
Electrical System
Value(s) Yes
Go to step 2.
Go to step 3.
<.2 Ω
Go to step 4
12 v Go to step 5
12 v+=AUX Go to step 5.
12 v-=MAIN
12 v+=AUX Replace fuel
12 v-=MAIN selector valve
12-47
No
Go to Power-
train OBD sys-
tem check.
Diagnose Fuel
lift pump first.
Repair open or
bad connection
in CKT 59
between fuel
selector switch
and IP ground
studs.
Repair open or
short to ground
in CKT 787 fuel
pump relay and
fuel selector
switch
Replace fuel
tank selector
switch and
recheck system.
Go to step 7.
4-1-00