Instrument Panel, Gauges and Warning Indicators: Description and Operation

INSTRUMENTS

DESCRIPTION

General
The instrument pack is a totally electronic device which receives analogue or digital signals via hardwired or bus systems for instrumentation operation. The instrument pack has two main functions:
^ To provide the driver information on vehicle status
^ To process and relay digital signals to and from other system controlling ECU's.

The signals are processed by two microprocessors which transpose the data into analogue gauge indications or warning lamp illumination.

OPERATION

Power Distribution
Feed from the positive battery terminal (C0192) is supplied to fuse 27, fuse 46, and fuse 53 of the passenger compartment fuse box (C0632) on an R wire. Fuse 27 (C0582) provides a constant battery feed to the Body Control Unit (BCU) (C0662) on an RP wire. Fuse 46 (C0586) provides two constant battery feeds to the instrument pack (C0230 & C0233) on a pair of RY wires.

Fuse 53 (C0583) provides a constant battery feed to the ignition switch (C0099 on Td6 vehicles, C0028 on V8 vehicles) on an R wire. When the ignition switch is turned to the 'auxiliary' position, current flows across the switch (C0099 on Td6 vehicles, C0028 on V8 vehicles) to fuse 45 of the passenger compartment fuse box (C0585) on a PB wire. Fuse 45 (C0586) provides an auxiliary ignition feed to the instrument pack (C0233) on a PG wire.

When the ignition switch is turned to the 'ignition' position, current flows across the switch (C0099 on Td6 vehicles, C0028 on V8 vehicles) to fuse 1 of the passenger compartment fuse box (C0585) on a G wire. Fuse 1 (C0587) provides two ignition feeds to the instrument pack (C0230 & C0233) on a pair of GU wires.

The instrument pack (C0230 & C0233) is earthed on NB wires.

Analogue Instruments

Speedometer
The ABS ECU (C0506) provides the instrument pack (C0230) a pulsed signal on an SB wire. The instrument pack calculates the vehicle speed from this signal and broadcasts it to other systems via the CAN, I, and K buses.

Tachometer
The instrument pack (C0234) receives an engine speed signal from the Engine Control Module (ECM) via the CAN bus on YN (low) and YB (high) wires.

Fuel Level Gauge
The instrument pack (C0234) provides a feed to the LH fuel tank level sensor (C0114) and the RH fuel tank level sensor (C0114) on BRW and BRY wires respectively. Each level sensor is a float operated potentiometer. By measuring the current returned on an NBW (LH) and an NBY (RH) wire, the instrument pack can determine how much fuel is in the tank.

Engine Coolant Temperature (ECT) Gauge
The instrument pack (C0234) provides a feed to the ECT sensor (C0169) on an NP wire. The ECT sensor is a Negative Temperature Coefficient (NTC) sensor. As ECT rises, the resistance of the sensor falls. By measuring the signal returned on an NY wire, the instrument pack can determine the ECT.