PONTIAC FIERO 1988 Service Repair Manual

6E3-CS-6 2.8L (VIN 5) DRIVEABILITY AND EMISSIONS
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DRIVEABILITY AND EMISSIONS 2.8L (VIN S) 6E3-C40-1
SECTION CIO
ECM CONTROLLED AIR CONDlTlOlUlNG
CONXENTS
GENERAL DESCRIPTION ................ C10-1 DIAGNOSIS ......................... C10-1
OPERATION ....................... C10-1 ON-CARSERVICE ..................... C10-1
GENERAL DESCRIPmON
In order to improve idle quality and wide open
throttle performance, the
NC compressor is controlled
by the ECM.
There are two different types of
AJC systems used
in
GM vehicles. One is referred to as C.C.O.T. (cycling
clutch orifice tube), which uses a fixed displacement
compressor. The other type of system uses a
compressor with
a variable displacement, and is
referred to as the V-5 type system. The V-5 type meets
A/C requirements without cycling. For descriptions of
both types, and an explanation of the components
used, refer to Section
"IB" of the service manual.
OPERATION
The 2.8L engine uses the C.C.O.T. type A/C
system, and is controlled by the ECM. When
NC is
requested, 12V power is supplied to the pressure
cycling switch and to the
NC power relay. The ECM
controls the
A/C clutch by energizing the A/C control
relay. This allows the
EChI to incrctlse idle speed
before turning on
NC to improve idle quality. The
high pressure cut-out switch (normally
closed) opens when head pressure gets too high. This
disables the
A/C clutch, before damage can occur to
the system. This switch opens, when pressure is
greater than about 440 psi (3034
kPa).
See CHART C-10 for diagnosis and wiring
diagram of the electrical portion of the
NC circuit.
DIAGNOSIS
CHART C-10 should be used for diagnosing the
electrical portion of the
A/C circuit. Section "1R"
should
be used for diagnosing the refrigerant portion
of the system.
The "Scan" tool will be used in diagnosing the
system, as it has the ability to read the
A/C request
input to the ECM, as well as displaying when the
ECM has commanded the
A/C clutch "ON".
ON-CAR SERVICE
For removal and replacement procedures of NC
components, refer to Section
" 1" of the service manual.

6E3-C10-2 2.8L (VIN S) DRIVEABILITY AND EMISSIONS
A/C CONTROL
DK GRNNVHT 59
CHART C-10
AIC CLUTCH CONTROL
2.8L (VIN S) "F" WRIES (PORT)
Circuit Description:
ECM control of the A/C clutch improves idle quality and performance by:
Delaying clutch apply
until the idle air rate is increased.
e Releasing clutch when idle speed is too low or during high power steering loilds.
e Releasing clutch a1 wide open throttle.
smooths cyclingof the compressor by providing additional fuel at the instant clutch
is applied.
Voltage is supplied to the
NC Clutch Control relay on CKT 59 by the NC Control Switch. This saine
voltage is supplied as a signal to ECM pit1 88. After a time delay of about 112 second the ECM twill ground
terminal
"A2," CKT 905, and close the A/C relay contacts.
When
relay is energi~etf battery vollage from CKT 59 is supplied to the IVC clulch lhroug11 Ihe txlay arid
CKT 959.
Test Description: Numbers below refer to circled
numbers on the diagnostic chart.
1. The ECM will only energize the A/C relay, when
the engine is running.
'I'his lest will determine if
the relay, or CK'F 905, is Sauity.
2. In order for the clutch to proper1.y be engaged, the
pressure cycling switch must bc closc!cl to provide
12 volts to the relay,
ilnd the high pressure switch
must be closed, so the
AlC rtquest (12 volts) wlll
be present at the ECNI.
3. Determines if the signal is ~.eachitlg the I4:CAI on
CKT 59 from the A/C control panel. Signal hhoitld
only be present when the AlC mode or tlcl'rost
mode has been selected.
4. A short to ground in any part ot' the A/C request
circuit, CKT
67 to the relay CKrI' 59, CKT 959 to
the NC clutch, or the
:2/C clutch, coulcl be the
cause
ofthe blown fiise.
5. With the ignition "ON" and the diagnostic
tcrminal grounded, the ECM should be grounding
CKT 905 which should cause the test light to be
"ON".
Diagnostic Aids:
If complaint was insufficient cooling, the problem
111~1,~ be ciiuscd by an inoperalive cooling fan. 'I'he
t!11gine cooling fan should turn "ON," when AlC is
"ON" ,tntl cZ/C head pressure exceeds about 233 psi. If
not. qctt: ("I Iclli'I' C-12 for diagnosing the cooling fan.

DRIVEABILITY AND EMISSIONS 2.8L (VIN S) 6E3-C10-3
@ DISCONNECT AIC RELAY.
PROBE CKT 905 WITH A
IN CKT66. IF AIC FUSE IS
BLOWN, CHECK CKTS 66,

6E3-CIO-4 2.8L (VIN S) DRIVEABILITY AND EMISSIONS
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DRIVEABILITY AND EMISSIONS 2.8L (VIN S) 6E3-C12-1
SECTION C12
COOLING FAN CONTROL
CONTENTS
GENERAL DESCRIPTION ................ C12-1 DIAGNOSIS ......................... C12-1
OPERATION ....................... C12-1 PARTS INFORMATION ................. C12-1
GENERAL DESCRIPTION DIAGNOSIS
The fan is used for engine and A/C condenser The following charts will diagnose the ECM
cooling but the fan only operates under certain controlledcoolingfan.
conditions.
PARTS INFORMATION OPERATION
PART NAME
GROUP The electric cooling fan on this engine is controlled
by the ECM. The ECM will ground the cooling fan Fan, Enginee.. ...................... 1.055
relay, which turns on the fan, when the following Motor,Fan.. .~~...~~~.~~~~.~~....~.. 1.055
conditions are met. Kelay, Engine Fan .................... 1.055
@ Coolant temperature sensor signal indicating a
temperature greater than 106°C (222°F).
@ Or: A/C head pressure greater than about 200 psi
and vehicle speed less than 40 tnph.
When the cooling fan is turned on, it will stay on
for
a minimum time of 15 seconds on the 2.8L.
@ The 2.81, also uses an override switch which will
also turn
on the cooling fan if the ECM fails.

CONNECTOR
TO ALTERNATOR
I.P.CONNECTOR
DK GRNNVHT 335
CHART C-12
(Page 1 of 2)
COOLING FAN CONTROL CIRCUIT
2.8L (VIN S) "F" SERIES (PORT)
Circuit Description:
'I'he electric cooling fan is controlled by the ECM, based on inputs from the coolant temperature sensor, the
NC fan control switch, and vehicle speed. 'I'he ECM controls the f~in by grounding CKT 335, which energizes
the fan control relay. Battery voltage is then supplied to the fan motor.
The ECM grounds
CKT 335, when coolant temp. is over about 106°C (223"F), or when AIC has been
requested, and the fan control switch opens with high
I\/C pressure, about 200 psi (1380 kPa). Once the ECM
turns the relay "ON", it will keep it "ON" for a nlinirnum of GO seconds, or until vehicle speed exceeds 70 mph.
Also, if Code
14 or 15 sets, or the ECM is in throttle body back up, the fan will run at all times.
On
kt vehicle not equipped with A/C, CK'I' 732 is,ju~rlperetl to ground so that Lhe fan does not run at all times.
Test Description: Numbers below refer to circled
numbers on the diagnostic chart,.
1. With the diagnostic terminal grounded, the
cooling
fan control driver will close, which should
energize the fan control
relay.
2. If the A/C fan control switch or circuit is open, the
fan would run whenever the engine is running.
3. With AIC clutch engaged, the i\lC fan control
switch should open, when
A/C high pressure
exceeds about
200 psi ( 1380 k13a). This signal
should cause the
ECM to energize the ran control
relay.
Diagnostic Aids:
If the owner complained of an overheating
problem, it
rnust he determined if the complaint was
clue to an actuill hoilover, or the hot light, or
temperature gage indicated over heating.
If the gage, or light, indicates overheating, but no
hoilover is detected, the gage circuit should he
checked.
'I'he gage accuracy can, also, be checked by
comparing the coolant sensor reading using a "Scan"
tool and comparing its reading with the gage reading.
If the engine is actually overheating, and the gage
indicates overheating, but the cooling fan is not
coming "ON", the coolant sensor has probably shifted
out
ofcalibration and should be replaced.
If
the engine is overheating, and the cooling fan is
"ON", the cooling system should hc checked.

DRIVEABILIW AND EMISSIONS 2.8L QViN S) 6E3-C12-3
D IDLE ENGINE.
L------A

6E3-C12-4 2.8L (VIN S) DRIVEABILITY AND EMISSIONS
I.P. HARNESS CONNECTOR
(FRONT VIEW)
TO ALTERNATOR
DK GRNNVHT 335
FAN CONTROL SWITCH
CHART C-12
(Page 2 of 2)
COOLING FAN CONTROL CIRCUIT
2.8L (VIN S) "F" SERIES (PORT)
Test Description: Numbers below refer to circled
The SES light should also be flashing, at this
numbers on the diagnostic chart.
point. If it isn't flashing, see
CHART A-2.
1. 12 volts should be available to both terminal "E" 3. If the fan docs not turn "ON", at this point, CKT
& "C", when the ignition is "ON". 936 or CKT 150 is open, or the cooling fan motor is
2. This test checks the ability of the ECM to ground
faulty.
CK'I' 335.

DRIVEABILITY AND EMISSIONS 2.8L (VIN S) 6E3-C12-5
CHART :
: C-12 :
ERMINALS WITH A TEST
THE COOLING FAN MOTOR
HARNESS CONNECTOR