T1000 L4-111 1.8L DSL (1983)
Fuel Gauge: Testing and Inspection
The fuel gauge system consists of a sending unit, instrument voltage regulator and an electric fuel gauge. The sending unit is a variable resistor that is
controlled by a float, and the float rises and falls in response to fuel level. When the ignition is on voltage is applied to the gauge through the voltage
regulator, and the gauge ground circuit is completed through the sending unit.
When the tank is full and the float is raised, maximum resistance (approximately 90 ohms) is produced by the sending unit, current flow through the
gauge is decreased, and the gauge pointer moves very little. As the tank empties and the float drops resistance in the sending unit decreases, current flow
through the gauge increases and the gauge pointer moves toward empty.
Most analog fuel gauges are of the free floating type, which means that the gauge pointer does not remain against the full stop when the ignition is off.
Rather, the pointer floats to a mid-position when no voltage is applied to the gauge.
TROUBLESHOOTING
Gauge Reads Empty When Tank Is Full
This condition is generally caused by a short in the tank unit circuit
1.
Disconnect electrical connector to sending unit, then turn on ignition.
2.
If gauge reads past full, test gauge with tester BT-6508 or equivalent. If gauge still reads empty, disconnect main body harness connector (near
fuse block).
3.
If gauge still shows empty, check for short in printed circuit or defective gauge. If gauge reads beyond full, reconnect front body harness
connector and disconnect rear body harness connector (in left wheel house).
4.
If gauge shows empty, locate and repair grounded wire in harness between front and rear body harness connectors. If gauge reads beyond full,
check for short between rear body harness connector, damaged float or defective sending unit.
Gauge Reads Full Or Beyond At All Times
This condition is generally caused by an open in the tank unit circuit.
1.
Check tank unit ground for proper contact with body or chassis and repair as needed.
2.
If tank unit ground is satisfactory, disconnect electrical connector at tank unit and connect a jumper wire from the harness side sensing wire to
ground, then turn on ignition.
3.
If gauge reads empty, remove fuel tank and inspect wiring to sending unit. If wiring and connections are satisfactory, replace tank unit.
4.
If gauge still shows full, disconnect front body harness connector and ground fuel gauge wire terminal in instrument panel side of connector.
5.
If gauge still reads full, check for loose connection in cluster, open (crack) in printed circuit or defective gauge. If gauge reads empty, locate and
repair open or poor connection between front body connector and tank unit connector.
Fuel Gauge Inaccurate
Tester BT-6508 or equivalent must be used to diagnose dash gauge malfunction
1.
Ensure battery is fully charged, disconnect electrical connector to tank unit and connect tester to between harness connector and suitable ground
following manufacturer's instructions.
2.
Set tester on empty then turn on ignition. Gauge should read empty or below.
3.
Set tester on full. Gauge should read full or above.
4.
If gauge does not respond to tester input, replace dash gauge. If gauge responds correctly, check for poor connections at tank unit, poor tank unit
ground or defective tank unit.
