1988 PONTIAC FIERO Service Repair Manual

INSTRUMENT PANEL: GAGES CLUSTER I P
C: FUEL GAGE ALMYS lNDlCPaTES
FULL
Disconnect the Fuel Tank Sender Unit connec-
tor. Turn Ignition Switch to RUN.
If the Fuel Gage now indicates FULL,
repairlreplace Fuel Gage Sender.
@ If the Fuel Gage still indicates EMPTY,
check PNK (30) wire (see schematic) for a
short to ground. Check the Instrument Clus-
ter Printed Circuit for flaws and the gage
connections. Replace Fuel Gage if the PNK
(30) wire, Printed Circuit, and gage connec-
tions are OK, (see Section 8C).
D: FUEL GAGE ALVVAYS lNDlCATES
EMPTY
At: FUEL TANK SENDER UNIT CONNECTOR
(HARNESS HALF)
(Disconnected)
1. Checklrepair PNK (30) wire (see sche-
matic) for an open. Check Instrument
Cluster Printed Circuit for flaws and for
clean and tight Fuel Gage connections.
Replace Fuel Gage if the above checks are
OK (see Section
8C).
2. Check BLK (150) wire for an open to
E: FUEL GAGE ACCURACY TEST
Disconnect the Fuel Tank Sender Unit connec-
tor and connect one red lead of
5-33431 tester to
terminal
B (PNK) and the other to te
(BLK) of the harness half of the connector. Set
the resistance dials of the tester to 0 ohms, 44
ohms and then to 90 ohms. The Fuel Gage
should read E,
I12 and then F.
If Fuel Gage responds correctly, replace
Fuel Gage Sender and its wires.
0 If Fuel Gage does not respond correctly,
check PNK (30) wire to the Instrument Clus-
ter Printed Circuit and BLK (150) wire for
high resistance. Also, inspect the Printed
Circuit for proper mating of connectors.
Replace the Fuel Gage if the wires and
Printed Circuit are good.
F: COOLANT TEMPERATURE GAGE
ALWAYS
INDICATES HOT
Disconnect the Coolant Temperature Sender
connector and place Ignition Switch in RUN.
@ If Coolant Temperature Gage reads cold,
replace the Coolant Temperature Sender.
0 If the Coolant Temperature Gage does not
read cold check DK GRN (35) wires and Igni-
tion Switch, terminal
61 of connector Cl for
a short to ground (see schematic). Replace
the Coolant Temperature Gage if
all are good
(see section
8C).
6: COOLANT TEMPERATURE GAGE
ALWYS INDICATES COLD
Disconnect the Coolant Temperature Sender
connector and jumper the DK GRN (35) wire to
ground. Put the Ignition Switch in RUN.
0 If the Coolant Temperature Gage reads hot,
replace the Coolant Temperature Sender.
If the Coolant Temperature Gage does not
read hot, check DK GRN (35) wire for
an
open. Replace the Coolant Temperature
Gage if the wire is good (see Section
8C).
H: COOLANT TEMPERATURE GAGE
ACCURACY TEST
Disconnect the Coolant Temperature Sender
connector. Connect one red clip lead of the
5-33431 tester to the harness connector DK
GRN (35) wire and the other red clip lead to
ground. Adjust the resistance dials of the tester
to 1254 ohms,
697 ohms and then to 54 ohms.
The Coolant Temperature Gage should show
100°F
(40°C), 220°F (100°C) and then 260°F
(130°C).
If the gage reads correctly, the wiring and
gage are good. Replace the Coolant Tem-
perature Sender.
If the gage is not correct check DK GRN (35)
wire and Printed Circuit. If they are good,
replace the Coolant Temperature Gage (see
Section
8C).

INSTRUMENT PANEL: GAGES CLUSTER
I: OIL PRESSURE GAGE ALWAYS
lEUDlCATES ZERO
At: OIL PRESSURE SENDER
Condition:
lanition Switch: RUN
Action
I Correct Result I For Diagnosis
If the result is correct, replace the Oil
Pressure Sender.
1. Check TAN (31) wire to Instrument Clus-
ter for a short to ground. Check Instru-
ment Cluster Printed Circuit for cracks or
flaws. Repairlreplace the Oil Pressure
Gage if the wire and Printed Circuit are
OK (see Section
86).
Disconnect Oil
Pressure
Sender
J: 81L PRESSURE GAGE ALWAYS
INDICATES
HBGH PRESSURE
(Disconnected)
high pressure
connector
Oil Pressure
Gage shows (Continued
from previous column)
See 1
Cluster Printed Circut for an open. If wire
K: OIL PRESSURE GAGE ACCURACY
TEST
Disconnect the Oil Pressure Sender. Connect
one red clip of the
5-33431 tester to the harness
connector, TAN (31) wire, and connect the other
red clip lead to ground. Set the resistance dials
of the sender to 0 ohms, 43 ohms and then to 90
ohms. The Oil Pressure Gage should read 0 psi
(0
Wa), 40 psi (280 kPa) and 80 psi (660 kPa)
with the V6 or 0 psi (0 kPa), 30 psi (210 kPa) and
60 psi (420
kPa) with the V8.
r If the gage reads correctly, replace the Oil
Pressure Sender.
@ If the gage does not read correctly, check the
TAN (31) wire and Printed Circuit. If they
are good, replace
the Oil Pressure Gage (see
Section 89.
L: VOLTMETER TEST
With the Ignition Switch in RUN, connect a
Voltmeter between the positive and negative
als of the Battery.
If the voltage reading on the test voltmeter
is
approfimately the same as the car's Volt-
meter, the car's Voltmeter is OK. If
the voltage reading on the test voltmeter
is different
from the car's Voltmeter, check
the Instrument Cluster Printed Circuit for
cracks or flaws. Repairlreplace the Volt-
meter if
all wires and Printed Circuit are OK
(see Section 8C).
M: TACHOMETER TEST
At: INSTRUMENT CLUSTER PRINTED
CIRCUIT CONNECTOR 61
(Disconnected)
Condition:
I @ Ignition Switch: RUN I --
For Diagnosis
Of incorrect
Between Results
1 (WRT) & Greater than See Ground 10 volts
@ If above voltage is corred, replace the
Tachometer.
1. Check WHT (121) wire md Tachometer
Filter to
Ignition Coil (see schematic). If
wire is OK, see Section 6D for further
diagnosis.
N: SPEEDOMETER TEST
1. Disconnect connector C207. Connect the
5-33431 tester to the harness half of the con-
nector,
terminal C (LT GRN) and to ground,
using the
5-33431-873 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 mph
+ 2
mph.
(Continued
in next column)
(Continued on next page)

(Continued from previous page)
If the Speedometer reads correctly, refer to
Vehicle Speed Sensor, Section
8A-33 for fur-
ther diagnosis.
If the Speedometer reads incorrectly, check
LT GRN (537) wire and the Instrument Clus-
ter Printed Circuit for opens. Replace the
Speedometer Assembly if the wire and
Printed Circuit are good (see Section
8C).
O: UPSHIFT INDICATOR WIRE TEST
Disconnect ECM connector C207. Put the Igni-
tion Switch in RUN and measure the voltage at
terminal
H (see section 8A-21 or 22).
If battery voltage is present, see section
6E
for ECM diagnosis.
If battery voltage is not present, check the
TANIBLK (422) wire for an open or short to
Ground.
CIRCUIT OPERATION
The operation of an indicator is explained in
the operation of the circuit it is apart of. See the
circuit referred to for a complete description of
that indicator and the other components that
work with it. Only the gages and indicators that
do not appear in other schematics are described
in this section.
Tachometer
The Tachometer displays engine speed in
rpm. Voltage pulses are taken from the Ignition
System and sent to the Tachometer. Solid State
circuits process these pulses into a signal that
drives the pointer of the meter. The Tachometer
responds to the frequency of the voltage pulses.
These pulses increase with engine speed.
Fuel Gage
The pointer of the Fuel Gage is moved by the
magnetic field of two coils. The coils are at right
angles to each other. Battery voltage is applied
to the E coil and the circuit divides at the
opposite end of this coil. One path continues to
ground through the F coil. Another goes to
ground through the variable resistor of the Fuel
Gage Sender Unit.
When the tank is low, the resistance of the
Fuel Gage Sender is low. A large flow of current
passes through the E coil and the Fuel Gage
Sender resistor. This moves the pointer
towards E on the scale. When the tank is
full,
the sender resistance is high. More current
flows through the F coil, moving the pointer
toward F on the scale.
With two coils operating the pointer, the Fuel
Gage is not affected by changes in the voltage
of the system.
011 Pressure Gage
The engine oil pressure is displayed by the Oil
Pressure Gage. The pointer of the gage is
moved by two coils, and its operation is similar
to that of the Fuel Gage. The
Oil Pressure Sender is connected to the
junction of the two coils.
It has low resistance
when the oil pressure is low, and 90 ohms
resistance when the oil pressure is high. This
changing resistance changes the current flow
through the coils. The magnetic fields of the
coils move the pointer to indicate high or low
coolant temperature.
Voltmeter
The Voltmeter measures the electrical sys-
tem voltage with the Ignition Switch in RUN,
BULB TEST, or START. With the engine
stopped, the Voltmeter indicates battery condi-
tion. With the engine
running, the Voltmeter
indicates Charging System operation.
Coolant Temperature Gage
The Coolant Temperature Gage is also oper-
ated by two coils. Battery voltage is applied to
both coils. One is grounded directly
and the
other is grounded through the Coolant Tem-
perature Sender. This has 54 ohms resistance at
260
OF, 130 "C (hot coolant) and its resistance
becomes greater at lower temperatures. It is
appr~ximately 1284 ohms at 100 OF (40 '6). This
causes the current through the sender and one
coil to vary as the coolant temperature charges
and this moves the pointer.

INSTRUMENT PANEL: GAGES CLUSTER
Speedorneter and Odometers
The Speedometer is operated by an electronic
circuit. The Vehicle Speed Sensor (VSS),
located in the transmission, generates an AC
voltage whose frequency is proportional to the
speed of the vehicle. This goes to the Vehicle
Speed Sensor Buffer and then to the Speedom-
eter circuit board in the Instrument Cluster.
The Solid State circuit drives the pointer of the
Speedometer. There is no speedometer cable
in
the vehicle.
The same speed signal from the Vehicle Speed
Buffer is processed by the Speedometer circuit
board to drive the Odometers. They are oper-
ated by a motor that responds to pulses from
the Speedometer circuit.
UpshiN Indicator
With Manual Transmission, the indicator
lights when the car should be shifted to the next
higher gear for better fuel economy. Battery
voltage is applied to one side of the bulb. The
other side of the bulb is switched to ground by
the ECM which uses engine data to compute an
efficient shift point.

INSTRUMENT PANEL: DIGITAL CLUSTER
I
I
I I SEE FUSE 20 AMP SEE FUSE I
BLOCK DETAILS
CIRCUIT SOLID STATE 00 NOT
MEASURE RESISTANCE

- INSTRUMENT PANEL: DlGlTAL CLUSTER
SEE GROUND
Gll8 - - -

INSTRUMENT PANEL: DIGITAL CLUSTER
GAGES
MAX PRESSURE

b INSTRUMENT PANEL: DIGITAL CLUSTER
INTERIOR Ll G HTS
SENSOR
- - -