Fuel Gauge - Diagnostic Guidelines: Overview
Bulletin # 87-018Section: Product
Dated: 5/4/87
Subject:
GUIDELINES WHEN DIAGNOSING FUEL GAUGE OPERATION
To: ALL RANGE ROVER DEARS
The following guidelines should be followed when diagnosing problems with fuel gauge operation:
COMPLAINT:
No fuel gauge reading or intermittent reading.
POSSIBLE CAUSES:
Multifunction unit
Gauge/gauge wiring
Sending unit/sending unit wiring.
The multifunction unit, attached to the rear of the binnacle, provides a stabilized voltage to both the fuel and temperature gauges. Failure of this device usually results in the simultaneous failure of both gauges. A quick test involves removing the green/black wire from the fuel gauge sending unit and measuring for voltage with the ignition switched on. Specification: 10.0 +/- 0.25V. Replace if out of tolerance.
The fuel gauge is supplied with stabilized voltage from the multi function unit via printed circuit and with a variable resistance signal through the green/black wire from the fuel gauge sending unit. Resistance values will range from approximately 19 ohms to 275 ohms, full to empty. These resistances complete the ground circuit to the gauge and cause a deflection of a bi-metallic strip attached to the gauge needle proportionate to the ohm values suppled.
The sending unit is a simple variable resistor connected to a float and rod. In order for its resistance signal to accurately reflect the correct fuel level the following checks should be made:
1) Float integrity, i.e. no fuel present in the float ball.
2) Float arm not bent, distorted or jammed against the fuel pump reservoir.
3) Resistance values as measure with an accurate ohm meter will vary from approximately 19-275 ohms (full to empty) with no opens throughout the range.
4) ground continuity present on the 2 wire (black & blue/black) sending unit plug.
A failure in any three of the above components will of course prevent the system from operating but just as importantly, a failure in the interconnecting wiring or circuit board wiring will have the same results. Always check point to point continuity when troubleshooting electrical problems.
COMPLAINT:
Fuel gauge operates but appears to be inaccurate.
POSSIBLE CAUSES:
1) Poor wiring connections, poor grounds.
2) Out of tolerance multi function unit.
3) Defective gauge
4) Defective sending unit/distorted float arm.