oil change PONTIAC FIERO 1988 Service Service Manual

BNS'TWUMENT PANEL: DIGITAL CLUSTER a B
(Continued from previous gage)
I: FUEL GAGE IS INACCUWTE
Disconnect the fuel tank unit connector C313
and connect the two red clip leads of tester
5-33431 to
terminals A (BLK) and B (PNK) of
the harness half of that connector
C313. Set the
resistance
dials of the tester to 0 ohms, 44 ohms
and then to 90 ohms. The Fuel display should
read
"E ", 11/2 and Full. Cycle the Ignition after
each resistance change.
If the display responds correctly, install a new
Fuel Gage Sender.
If the display does not respond correctly,
check the PNK (30) wire between the fuel
tank and the Instrument Cluster for high
resistance.
If this wire is OK, replace the
Instrument Cluster (see Section
8C).
J: OIL PRESSURE DISIDWY READS
ZERO
Check the oil pressure with a manual gage. If the
pressure is correct, continue with the electrical
diagnosis.
Remove the connector from the Oil Pressure
Sender.
If the display now shows high pressure, the
wiring is good. Install a new Oil Pressure
Sender.
If the display remains low, check for a short
in the TAN (31)
wire between the sender and
the Instrument Cluster. If that wire is not
shorted to ground, replace the Instrument
Cluster (see Section
8C).
K: OIL PRESSURE DISPWY RWDS
MMlMklM PRESSURE
Disconnect the connector from the Oil Pressure
Sender and jumper the TAN (31) wire to
ground. Put the Ignition Switch in RUN.
If the display now reads low, the wiring is
good. Install a new
Oil Pressure Sender.
* If the display remains high, check for an
open in the TAN (31) wire back to the Instru-
ment Cluster. If that wire is good, replace
the Instrument Cluster (see Section
8C).
L: OIL PRESSURE BlSPLAV IS
llUAGCll RATE
Disconnect the connector from the Oil Pressure
Sender and connect one red clip lead from tester
5-3343
1 to the TAN (3 1) wire terminal. Connect
the other red clip lead to ground. Set the
resistance dials of the
testor to 0 ohms, 43 ohms
and then to 90 ohms. The display should read 0
PSI (0
kPa), 40 PSI (280 kPa) and 80 PSI (660
kPa) with the V6 or 0 PSI (0 kPa) 130 PSI (210
kPa) and 60 PSI (420 kPa) with the V8.
r If the display is correct, install a new Oil Pres-
sure Sender.
If the display is not correct, check the TAN
(31) wire for high resistance (no more than
1
ohm). If is is good, replace the Instrument
Cluster (see Section
8C).
M: SPEEDOMETER BEST
(533431 -873 conneetor available)
1. Disconnect connector C207. Connect the
5-33431 tester to the harness
half of the
connector, terminal
C (LT GRN and ground
using the
533431-873 harness connector or
equivalent). With the tester set to
ON, 54
mph, 60
Hz and the Ignition Switch in RUN,
the Speedometer should read 54
qh + 2
mph.
If the Speedometer reads correctly, refer to
Vehicle Speed Sensor, Section
8A-33 for fur-
ther diagnosis.
If the Speedometer reads incorrectly, check
DK GRN (389) wire and the Instrument
Cluster Printed Circuit for opens. Replace
the Instrument Cluster if the wire and
Printed Circuit are good (see Section
8C).
N: UPSHIFT lNDlCATOR WIRE TEST
Disconnect ECM connector C207. Put the Igni-
tion Switch
in RUN and measure the voltage at
terminal
N (see Section 8A-21,221.
If battery voltage is present, see Section 6E
for ECM diagnosis.
If battery voltage is not present, check the
TANIBLK (456) wire for an open or short to
ground.

INSTRUMENT PANEL: DIGITAL CLUSTER n 23 rn E
ClRCUlT OPERATION
The Instrument Cluster uses a microprocessor
to develop data for fuel supply, coolant tem-
perature, oil pressure, voltage, engine rpm, and
vehicle speed. The Digital Cluster also contains
an Odometer, Warning Indicators, and an Audi-
ble Alarm. The Audible Alarm signals low oil
pressure, high temperature, low or high voltage,
and low fuel.
With the Ignition Switch in RUN, voltage is
applied through the GAGES Fuse to the Battery
Power inputs of the Instrument Cluster. With the
Light Switch in PARK or HEAD, voltage is ap-
plied at all times to the Lights On Dim Input.
The car's speed is displayed in mph or
krnh by
selecting either English or Metric with the
En-
glishNetric selector switch.
Gages and Audible Alarm
With the Ignition Switch in RUN, voltage is
applied through the GAGES Fuse to the Battery
Power Input terminal. With the Light Switch in
PARK or HEAD, voltage is applied at all times
to the Lights On Dim Input.
Fuel Display
The Fuel Display Sender provides a signal to
the cluster that is related to fuel level. With a
full tank the resistance is 90 ohms, and with an
empty tank the resistance is less than
1 ohm.
The microprocessor converts this signal and
activates a 12 segment bar graph which dis-
plays the fuel level. When the bar graph fuel
gage display changes from two segments to
one, the Audible Alarm beeps briefly.
Oil Pressure Display
The Oil Pressure Sender, with a resistance of
0 to 90 ohms, sends a signal to the cluster that is
related
to oil pressure. At zero pressure (0 PSI),
resistance is 0 ohms, and at maximum pressure
(80 PSI), resistance is approximately 90 ohms.
The microprocessor converts the signal and
activates a 12 segment bar graph which dis-
plays the oil pressure. When the bar graph
changes from two segments to one segment
(approximately
4 PSI), the Audible Alarm
beeps briefly.
kmperature Display
The Coolant Temperature Sender sends a sig-
nal to the Instrument Cluster that is related to
coolant temperature. Coolant Temperature
Sender resistance drops from 1,365 ohms at
100°F
(38"C), to 55 ohms at 260°F (127°C). The
temperature display is a bar graph display with
12 segments. When the bar graph changes to all
segments activated (hot coolant temperature),
the Audible Alarm beeps.
Volts Display
The microprocessor in the gages module re-
ceives a signal from the Battery Power Input ter-
minal. This signal activates the 12 segment bar
graph volts display. The volts gage ranges from 8
volts
(1 segment lit) to 18 volts (all segments lit).
Under idling and normal driving conditions, 7 or
8 segments are lit. When the volts gage displays
less than
4 segments or more than 12 segments,
the Audible Alarm beeps.
Tachometer
The Thchometer displays engine speed in rpm.
Voltage pulses are taken from the
Ignition Sys-
tem and sent to the Tachometer. Solid state cir-
cuits process these pulses into a signal that con-
trols the Tachometer display. The Tachometer
responds to the frequency of the voltage pulses,
the number of pulses in a second. This increases
with engine speed. The
'Pdchometer Filter in the
circuit rounds off the pulses and removes voltage
spikes.
Speedometer
The digital Speedometer is operated by an
electronic circuit. The Vehicle Speed Sensor, lo-
cated in the Transmission, generates an AC volt-
age whose frequency is proportional to the speed
of the vehicle. This goes to the Vehicle Speed
Sensor Buffer and then to the Speedometer cir-
cuit board in the Instrument Cluster. The solid
state circuit processes this signal into a control
signal for the Speedometer display.
Odometer
The digital Odometer display is operated by an
electronic circuit. The Vehicle Speed Sensor, lo-
cated in the Transmission, generates an
AC volt-
age whose frequency is proportional to miles
(kilometers) traveled. This goes to the Buffer
and then to the Odometer circuit board in the
Instrument Cluster. The solid state circuit
processes this signal into a control signal for
the Odometer display. Distance Data is stored
in
NV RAM Chip.

98-2 CRUISE CONTROL
Fig. 1 Multi-Function Lever
e The Set Position - With the button switch
depressed and then released (car speed must
exceed the low speed limit point, and the
Off/On/Resume/Accel Switch must be in the
ON position) the cruise speed will be set at the
speed the car was at when the button was
released. Car cruise speed will be within
& 1 mph
of the actual speed at engaged speed. The system
will cruise until either the
Off/On/Resume/Accel Switch is moved to OFF,
the ignition switch is turned off, and/or the
Set/Coast Button is pushed in fully and held.
Pushing the brake pedal (or clutch pedal) releases
the cruise but not the resume capability.
The Coast Position - With the button switch
fully depressed, the driver can raise or lower his
speed. To increase speed, the driver can
accelerate to a new speed, fully depress the switch
and release the button. The controller "forgets"
the previously set speed. An increased control
speed can also be more easily set by the
Off/On/Resume/Accel Switch as previously
described. To decrease cruise speed, the button
switch is held in, disengaging the cruise system,
which allows the throttle to return to the idle
position. When the car has slowed to the aesired
cruise speed, releasing the switch will re-engage
the system.
e The "Tap-Down" Position - In order to do
this the cruise must be engaged and operating.
"Tapping-down" is done by quickly pressing and
releasing the
Set/Coast Button, or "tapping" the
button. Do not hold the button in the depressed
position or the system will go into the "coast"
mode. "Tap-down" is a function in which cruise
speed can be decreased by
1 mph increments (one
tap = 1 mph decrease).
The accelerator may be depressed at any
time
to override the cruise system.
Release of the accelerator will return the
car
te the previous set cruise speed.
NOTICE:
To keep the vehic:e under control, and
to prevent possible vehicle damage, it is not
advisable to use the cruise control on slippery
roads. It is not recommended to use the cruise
control in conditions such as on winding roads or
in traffic of heavy or varying volume. When
traveling down
a steeply graded hill, the cruise control
should be disengaged by depressing the
bralte pedal lightly. The transmission can then be
shifted into a lower gear range to help control
vehicle speed.
ELECTRONIC CONTROLLER (MODULE)
Figure 2
Fig. 2 Controller (Module)
The controller interprets the position of the servo,
the position of the control switches and the output of
the speed sensor. In response to these inputs, the
controller electrically signals the opening or closing of
the vent and vacuum solenoid valves in the servo.
The controller is usually mounted on the pedal
bracket, but is integral with the ECM on some models
with certain engines. For specific location, see the
On-Car Service portion of this section.
SERVO UNIT
Figure 3
The servo consists of a vacuum operated
diaphragm, a normally open solenoid valve to vent the
diaphragm chamber to atmosphere, a normally closed
solenoid valve to connect the diaphragm chamber to
the vacuum source, and a variable inductance position
sensor.
The servo incorporates a steel core which moves
within a coil. Its resulting variable inductance provides
a continuous (voltage) servo position signal to the
controller. This voltage signal is constantly compared
to the vehicle speed signal. This comparison
determines if the cruise system has corrected the speed
error or if additional changes are required.
The servo operates the throttle in response to
signals from the electronic controller as follows:
Steady Cruise State (system engaged and
operating)
- Both vacuum and vent valves are
closed or sealed. The servo has a constant vacuum
on the diaphragm and places no requirements on
the vacuum source, as vacuum is trapped in the
diaphragm chamber.
e Vehicle Losing Speed (due to steep grades or
driver wishes to increase speed by using the Accel
or 'tap-up' feature)
- The controller energizes the
vacuum solenoid to open the vacuum valve to the
vacuum source. This increases the vacuum level