Pontiac Fiero 1988 Service Manual page 1215

8C4 INSTRUMENT PANEL, GAGES & CONSOLE
GENERAL DESCRIPTION
INSTRUMENT PANEL AND GAGES
Figures 801 and 802
The instrument panel is a single unit design and
all parts attach to the main instrument panel with clips
and screws. To service the instrument panel and
components see specific item information.
QUARTZ ELECTRIC SPEEDOMETER
The quartz electric speedometer and odometer
assembly displays the speed of the vehicle, total vehicle
mileage, and trip mileage. A conventional dial and
pointer assembly, along with odometer wheels, are
used to display this information. However, improved
drive methods are used in place of the standard drive
system, thereby eliminating the need for the
conventional speedometer cable.
To provide accurate vehicle information, the
quartz speedometer utilizes an accurate clock signal
supplied by a quartz crystal, along with integrated
electronic circuitry to process an electrical speed
signal. The speed signal is used by the circuitry to drive
the air core gage and odometer stepper motor. The
electrical speed signal is generated by a Permanent
Magnet (PM) generator mounted in the transmission.
This speed signal is transmitted to the speedometer
assembly buffering circuit contained in the instrument
cluster circuitry.
TACHOMETER
The tachometer indicates speed of the engine in
revolutions per minute (RPM). The engine can safely
be operated up to a maximum RPM as indicated by the
start of the red bar. Engine operation causing
tachometer readings in the red area can lead to serious
engine damage.
Due to its dual-coil design, ' the
tachometer may not return to zero when the
ignition is turned off. This is a normal
condition and should not be diagnosed as a
problem in the tachometer.
PM GENERATOR SPEED SENSOR
Figure 803
The PM generator is a permanent magnet
generator mounted in the transmission and is used to
provide vehicle speed data. It is designed to be used
with quartz and digital speedometers and will replace
the current transmission speedometer drive gear and
sleeve. The purpose of the PM generator is to provide
a speed signal that is proportional to vehicle speed.
This signal is transmitted directly to the speedometer
circuitry.
ODOMETER ASSEMBLY
The odometer assembly consists of conventional
odometer wheels driven by an electric stepper motor.
The stepper motor receives a frequency from the
speedometer circuitry. This signal controls the rate at
which the motor turns the odometer gears.
Trip Odometer
The trip odometer can be reset by
twice
fully
depressing the push button located on the right side of
the speedometer cluster. The first depression shows all
zeroes, and the second locks them in position. Both
depressions must be done to avoid possible half cycling
of the trip odometer. A slow, steady push should be
used to avoid damage to the internal mechanism.
Do not reset the odometer
w i t h
the vehicle in
motion. Damage to the odometer may occur.
SPEEDOMETER CIRCUIT BOARD ASSEMBLY
The circuit consists of two custom designed
integrated circuit chips, a crystal oscillator, and some
discrete electrical components. The basic function of
the circuit is to receive an incoming speed signal and
output a wave signal to drive the speedometer air core
gage mechanism and odometer stepper motor.
INSTRUMENTS
Instruments consist of fuel gage, temperature
indicator gage, generator (voltmeter) gage, oil pressure
indicator gage, speedometer, and tachometer. Service
on instruments can be obtained through authorized
repair stations. However, knowledge of instrument
circuit checks will help in determining if operating
difficulties lie in the instrument itself or its related
circuit.
Instruments have been designed for easy removal
by elimination of separate wiring. With the wiring
provisions integrated with the instrument panel wiring,
the instruments can be removed after removing the
trim and lens.
FUEL GAGE
An electrical fuel gage is used, consisting of an
instrument panel gage and a fuel tank pick-up. The fuel
gage indicates the quantity of fuel in tank only when
Ignition switch Is turned to "ON" or "ACCESSORY"
positions.
When ignition is turned to "OFF" or "START"
positions, the pointer may come to rest at any position.
The letters "E" and " F " on the fuel gage are used to
point out direction of indicator travel only.
Gage readings indicated by five graduations on
the gage face. The left hand line indicates empty, the
centerline half-full and the right line full.
SHIFT INDICATOR LIGHT
Vehicles with manual transmission have an
"Upshift" on the instrument panel. This light is
illuminated to indicate optimum shift points
throughout the range from optimum fuel economy to
optimum performance. When this light is on, shift your
transmission to th next higher gear range if conditions
permit. For fuel economy, accelerate slowly and shift
when the light goes on. For performance, accelerate as
desired and shift when the light goes on.