1988 PONTIAC FIERO sensor

CRUISE CONTROL
TROUBLESHOOTING HINTS
Try the following checks before doing the Sys-
tem Check
.
1 . Check vacuum hose for leaks. kinks. andlor
restrictions . Also check Cruise Control
Servo linkage
. Refer to Section 9 for vacuum
hose routing and servo linkage adjustments
.
2 . If the system works except for the Tap-Up
and
TapDown functions. replace the Cruise
Control Module
.
Go to System Check for a guide to normal
operation
.
Go to System Diagnosis for diagnostic tests .
SYSTEM CHECK (ROAD TEST)
Use the System Check Table as a guide to
normal operation
.
COMPONENT LOCATION Page-Figure
Brake Switch
.................... Above brake pedal. on brake pedal support ..... 201- 9-A
Check Valve
..................... Behind engine. to right of master brake cylinder . 201-15-A
Clutch Switch
................... Above clutch pedal. on clutch pedal support .... 201-10-B
Cruise Control Module
............ Behind RH side of IIP ...................... 201-11-A
Cruise Control Servo .............. LH front of engine compartment ............. 201-15-A
Fuse Block
...................... Behind LH side of IIP. below light switch ....... 201-10-A
Vacuum Release Valve
............ Above brake pedal. on brake pedal support ..... 201-10-B
Vacuum Tank ................... Lower LH front corner of engine compartment .. 201-15-A
Vehicle Speed Sensor Buffer
....... Behind RH side of IIP. near ECM ............. 201-13-A
C203 (6 cavities) ................. Behind LH side of IIP. at base of steering column 201-11-A
C207 (15 cavities) ................ Behind RH side of IIP. near ECM ............. 201-13-A
C209 (2 cavities) ................. Behind RH side of IIP. left of Cruise Control
................................. Module 201-11-A
C223 (4 cavities) ................. Behind LH side of IIP. at base of steering column 201-11-A
6102 .......................... LN rear corner of engine compartment ......... 201-15-A
6118 (VIN E)
................... Rear of RH cylinder head .................... 201- 5-B
6118 (VIN F) (VIN 8)
............. Rear of RN cylinder head .................... 201- 5-A
6118 (VIN S)
.................... Rear of RN cylinder head .................... 201- 1-C
S143 (VIN E) .................... Engine harness. RH front of dash ............. 201- 2-A
S143 (VIN
F) (VIN 8) ............. Engine harness. RN front of dash ............. 201- 6-A
S143 (VIN S)
.................... Engine harness. center front of dash ........... 201- 1-A
S204
........................... IIP harness. behind instrument cluster ......... 201-10-A
S217
........................... IIP harness. behind center of IIP .............. 201-10-A
S238
........................... Cruise control harness. near Brake Switch ...... 201-11-A
SYSTEM CHECK TABLE
Car should maintain speed
(Continued on facing page)

CRUISE CONTROL
(Continued from previous page)
TEST I: RIA CIRCUIT OPEN
Disconnect C223 and check switch continuity
between terminals A (BLU) and C (YEL) of the
pin half of the Cruise Switch in RIA.
0 If the switch is open, replace the Multi-Func-
tion Lever.
If the switch is not open, check for an open in
the
GRYIBLK (87) wire between terminal C
of connector C223 at terminal M of the Mod-
ule.
TEST J: VENT CIRCUIT SHORT
Remove the connector from the Servo and mea-
sure resistance between terminals
A and C of
the Servo.
If it is less than 30 ohms, replace the Servo.
If it is 30 ohms or more, check for a short to
ground in the DK
BLUIWHT wire from ter-
minal C of the Module to terminal A of the
Servo.
TEST K: VSS ClRCUlT OPEN
If the VSS light does not come on, or the volt-
age between terminals A (GRY) and D (BRN)
remains less than 7 volts, check for an open in
the BRN (437) wire or the RED (381) wire from
the Vehicle Speed Sensor Buffer. Refer to page
33-0 for diagnosis of Vehicle Speed Sensor.
TEST L: VSS CIRCUIT SHORT
If the VSS lights does not go off or Battery
voltage remains between ter
and D
(BRN), check for a short to ground on the
BRN (437) wire or the RED (381) wire from the
Vehicle Speed Sensor Buffer. Refer to page 33-0
for diagnosis of Vehicle Speed Sensor.
TEST M: VACUUM SYSTEM
1. Check for a blocked or leaking vacuum
source.
2. If the vacuum source is good, plug the Vac-
uum Release Port and repeat Test
6 of the
Isolation Test.
If the vacuum now holds the throttle open,
replace or repair the Vacuum Release Valve
or the hose to it.
If the test still fails, replace the Cruise Con-
trol Servo.
TEST N: SPS CIRCUIT SHORT
Disconnect the Cruise Control Servo connector
and repeat Test 7 of the Isolation Test.
If the resistance is now over range, replace
the Cruise Control Servo.
If the resistance is still low, find and repair
the short in the TAN wire from terminal F of
the Cruise Control Module to terminal B of
the Cruise Control Servo.
ClRCUlT OPERATION
The Cruise Control System operates a
mechanical linkage to the throttle by means of a
Vacuum Motor. This is a diaphragm moved by
a vacuum applied to one side. A solenoid oper-
ated valve connects the Vacuum Motor to a
Vacuum Tank. Another solenoid valve vents
the vacuum to reduce the suction. The Cruise
Control Module controls the Vacuum Motor
and the throttle by pulsing these solenoid
valves on and off.
One input to the Module is the vehicle speed.
This input comes from the Vehicle Speed Sen-
sor. If the actual speed signal is different from
the speed that was set into and remembered by
the Module, the Module generates pulses to
change the vacuum and return the vehicle to
the set speed. The Vehicle Speed Sensor is
mounted on the Transmission. Other inputs to
the Module are from the Cruise Switch and the
Set Switch. A disengage input to the Module
comes from a switch on the brake pedal. A
sepe-
rate vacuum shut down of the Cruise Control
comes from the Vacuum Release Valve on the
brake pedal.
The two outputs of the Cruise Control Mod-
ule operate the coils of the Vacuum Valve and
the Vent Valve. Both valves are located in the
Cruise Control Servo. These valves move the
throttle be means of the Vacuum Motor. The
Servo Position Sensor
(SPS) coil senses the
position and motion of the Vacuum Motor. It
feeds this information back to the Module to
provide smooth acceleration while the vehicle is
in Cruise Control.

(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.

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

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.

AUTOMATIC DAY-NIGHT MIRROR
(Continued from previous page)
SYSTEM DIAGNOSIS
0 Do the tests below if the Automatic Day-Night
Mirror does not operate correctly.
AUTOMATIC DAY-NIGHT MIRROR
VOLTAGE TEST
CONNECTOR (Disconnected)
1. Check BLK and LT GRN (24) wires for an
open. If Back Up lights do not operate,
check Gear Selector Switch adjustment
(automatic) or Back Up Switch
adjust-
:Continued from previous column)
2. Check Gear Selector Switch adjustment
(automatic) or Back Up Switch adjust-
ment (manual). Replace suspect switch if
adjustment does not correct the problem.
3. Check BLK and RED (39) wire for an
open.
4. Check BLK (150) wire for an open.
CIRCUIT OPERATION
The Automatic Day-Night Mirror is auto-
matically moved to the DAY and NIGHT posi-
tions as light conditions change. The Headlight
and Ambient Sensors read the light conditions
and feed this information to the solid state
mir-
ror control unit. The control unit activates the
Motor that drives the mirror.
With the Gear Selector
in Reverse, battery
voltage is applied through the Gear Selector
Switch or Back Up Switch to the reset input of
the mirror. If the mirror is in the NIGHT posi-
tion,
it changes to the DAY position. This pro-
vides a clear view for backing the car.
A distance or sensitivity control changes the
brightness required from the headlights of the
car behind to cause the
mirror to shift to the
NIGHT position.