Instruments (Speedometer): Description and operation
- Make
- MG
- Model
- TF Factory Workshop Manual
- Year
- 2002–2005
- Section
- Description and operation › Speedometer
Speedometer
The speedometer is operated electronically by a signal output from a speed transducer fitted to the gearbox. The transducer output is shared with the EPAS ECU.
Odometer and trip distance is displayed on an LCD located at the bottom of the speedometer. A button allows the trip and odometer to be displayed individually. The button will also reset the trip meter if pressed and held. The LCD also shows gearbox information when the vehicle is fitted with a Stepspeed (Em-CVT) gearbox.
Tachometer
The tachometer signal is taken from the MEMS ECU to the control board which is secured to the rear of the tachometer sub-assembly. The instrument panel display reading is averaged over all the engine cylinders to reduce fluctuations due to individual cylinder retardation in spark timing which may occur on engines fitted with programmed ignition systems.
Fuel gauge
The fuel gauge is driven by an air cored electronic movement which is fluid damped. Fluid damping reduces the movement of the gauge pointer caused by fluid movement in the tank.
The fuel tank gauge unit comprises a float and is connected to a wire-wound resistor which is connected to the fuel gauge and back through the instrument panel to earth. The resistor controls the current flow through to the fuel gauge circuit, which in turn drives the gauge movement against the resistance of the fluid damping.
When the gauge unit float is at its lowest point, indicating an empty fuel tank, the resistance to earth is at its greatest. The resistance value to fuel gauge position to earth is:
| Sender resistance | Fuel gauge position |
|---|---|
| 105 Ω | Empty |
| 32.5 Ω | Half full |
| 5 Ω | Full |
The fuel gauge pointer will display the level of fuel in the tank when the ignition was last switched off.
Coolant temperature gauge
The coolant temperature gauge is fitted with a return magnet causing the gauge to return to zero when the ignition is switched off.
| Thermistor resistance | Temperature | Gauge position |
|---|---|---|
| 142 Ω | 56°C | No movement |
| 49 - 98 Ω | 65°C - 85°C | Approx. one third |
| 24.6 - 32.1 Ω | 100°C - 110°C | Approx. halfway |
| 16.9 Ω | 125°C | Enters red sector |
Instrument illumination
Four bulbs provide instrument illumination, 2 x 14V, 1.4W for back illumination and 2 x 14V, 1.4W for front illumination.
Operation
For operation of the instrument pack. See ELECTRICAL REFERENCE LIBRARY, Description and Operation.
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