GMC 4000 Series Service Manual page 477

Sec. 8A
Page 466
FUEL TANK A N D EXHAUST
FUEL GAUGE SYSTEM TROUBLE DIAGNOSIS CHART
W IR IN G C O N N E C T O R
T A N K J
U N IT i tjJ
R E SIST O R ' 1 ------ 1 +
L A N ^ H V \
a
FULL SLIDER
C l ' ' '
E M P T Y ^
Fuel G auge System Wiring Diagram
PROBABLE CAUSE
Loose connection anywhere in circuit
1 .
2. Poor dash fuel gauge calibration
3. Poor tank unit calibration
4. Circuit grounded in resistor of tank unit
5. Circuit grounded between tank unit
resistor and dash gauge
6. Circuit within dash gauge grounded.
7. Circuit grounded between battery and
dash gauge.
8. Open circuit between ignition switch
and dash gauge
9. Open circuit between ground terminal
on gauge and ground
10. Open circuit between sending unit
terminal on dash gauge and
resistor terminal on tank unit
11. Open circuit in resistor of tank unit at
1/4 full position
12. Open circuit between tank unit slider
resistor and ground
13. Needle rubbing on face of gauge
14. Fuel tank float hang-up
15. Top of fuel tank deformed
16. Bottom of fuel tank deformed
17. Tank unit mounting flange bent
* Ignition switch must be "OFF" before removing tank sending unit, otherwise full battery voltage may des­
troy unit or ignite fuel vapors. For maximum safety, remove cable from negative battery terminal.
G M C S E R V I C E M A N U A L
AT D A S H
IG N IT IO N S W IT C H
/
f
i
- X
BATTERY
/
/
7 2398
/ W
/ M ?
A ?
X
X
X
x
POSSIBLE COMPLAINT
S / < > /
> / p V V * / o S /
^ y ^ y ^ y ^ y ^ y ^ y § y ^ y
w l w #
y .
SUGGESTED REMEDIES
y
r
Inspect and, if necessary, clean and
X
tighten all connections in circuit
Install new dash fuel gauge
X
Install new tank unit
X
Install new tank unit*
X
X
Insulate grounded circuit
X
Install new dash fuel gauge
X
Insulate grounded circuit
X
Clean and tighten appropriate
X
terminals or repair broken wire
Clean and tighten mounting bracket
X
where contact is made between
dash gauge and ground
Clean and tighten appropriate
X
terminals or repair broken wire
Install new tank unit*
Install new tank unit *
X
Position needle to prevent contact
X
X X X X
with face or install new gauge
Free binding float or install new
X
X X X
X
tank unit *
Straighten tank top or replace tank
X
Straighten bottom of tank or replace
tank
Straighten mounting flange or r e ­
X X
place tank unit*
/
*