PONTIAC FIERO 1988 Service Repair Manual

6EZ-B-4 5.OL (VIN E) DRIVEABILITY AND EMISSIONS
DEWNATION 1 SPARK KNOCK
Definition: A mild to severe ping, usually worse under acceleration. The
engine makes sharp metallic knocks that change with throttle opening.
@ CHECK for obvious overheatingproblems. - For proper transmission shift points. See Section
- Low coolant. "7".
- Loose water pump belt. - TCC operation. See CHART C-8.
- Restricted air flow to radiator, or restricted - For incorrect basic engine parts such as cam,
water flow thru radiator. heads,
pistons, etc.
- Faulty or incorrect thermostat. - Excessive oil entering combustion chamber.
- Coolant sensor, which has shifted in value. @ Remove carbon with top engine cleaner. Follow
- Correct coolant solution - should be a 50150 instructions on can.
mix of GM
#lo52753 anti-freeze coolant (or @ If there is spray from only one injector, then there
equiv.) and water. is
a malfunction in the injector assembly, or in the
@ CHECK: signal to the injector assembly. The malfunction
- For poor fuel quality, proper octane rating. can be isolated by switching the injector
- For correct PROM. connectors. If the problem remains with the
- Spark plugs for correct heat range.
original injector, after switching the connector,
- ESC system opeation. See CHART C-5.
then the injector is defective. Replace the injector.
- Ignition timing. See Vehicle Emission Control
If the problem moves with the injector connector,
Information label. then the
problem is an improper signal in the
- Fuel system for low pressure. See CHART A-7.
injector circuits. See CHART A-3.
- Check EGR svstem. - CHART C-7.
HESITATION, SAG, STUMBLE
Definition: Momentary lack of response as the accelerator is pushed down.
Can occur at all car speeds.
C'sually most severe when first trying to make the car
move, as from a stop sign.
May cause the engine to stall if severe enough.
@ Perform careful visual (physical) check, as Information" label.
described at start of Section
"B". - Generator output voltage. Repair if less than 9 or
@ CHECK: more than 16 volts.
- Fuel pressure. See CHART A-7. - For open ignition system ground, CKT 453.
- Water contaminated fuel. - Canister purge system for proper operation. See
- TPS for binding or sticking.
Section "C3".
- Ignition timing. See "Emission Control - EGR valve operation, CHART C-7.
CU"F OUT, MISSES
Definition: Steady pulsation or jerking that follows engine
speed, usually more pronounced as engine load increases. The
exhaust has a steady spitting sound at idle or low speed.
@ Perform careful visual (physical) check, us
described at start of Section
"B".
@ If ignition system is suspected of causing a miss
at idle or cutting, out under load:
@ Check for missing cylinder by:
1. Disconnect IAC motor. Start engine.
Remove one spark plug wire at a time, using
insulated pliers.
2. If there is an rpm drop on all cylinders, (equal
to within 50
rpm), go to "Rough, Unstable, Or
Incorrect Idle, Or Stalling" symptom.
Reconnect
IAC motor.
3. If there is no rpm drop on one or more
cylinders, or excessive variation in drop, check
for spark, on the suspected
cylinder(s) with J
26792 (ST-1251 spark tester or equivalent. If no
spark, see Section
"6D" for "Intermittent Operation
or Miss". If there is spark, remove spark plug(s) in
these cylinders and check for:
- Cracks
- Wear
- Improper gap
- Burned electrodes
- Heavy deposits
- Perform compression check on
questionable cylinder.
@ Check wire resistance (shoulcl not exceed 30,000
ohms), also, check rotor and distributor cap.

DRIVEABILITY AND EMISSIONS 5.OL (VIN E) 6E2-B-5
@ If the previous checks did not find the problem:
- Visually inspect ignition system for moisture,
dust, cracks, burns, etc. Spray plug wires with
fine water mist to check for shorts.
- Fuel System - Plugged fuel filter, water, low
pressure. See CHART A-7.
- Perform compression check.
- Valve timing.
- Remove rocker covers. Check for bent pushrods,
worn rocker arms, broken or weak valve springs,
worn camshaft lobes. Repair as necessary. See
Section
"6A".
If there is spray from only one injector, then,
there is
a malfunction in the injector assembly,
or in the signal to the injector assembly. The
malfunction can be isolated by switching the
injector connectors. If the problem remains with
the original injector, after switching the
connector, then the injector is defective. Replace
the iniector. If the
~roblem moves with the
injector connector, then, the problem is an
improper signal in the injector circuits. See
CHART A-3.
POOR FUEL ECONOMY
Definition: Fuel economy, as measured by an actual road test, is
noticeably lower than expected. Also, economy is noticeably lower than it
was on this car at one time, as previously shown by an actual road test.
@ CHECK: @ Visually (physically) check:
- Engine thermostat for faulty part (always open) - Vacuum hoses for splits, kinks, and proper
or for wrong heat range. See Section
"6B". connections, as shown on Vehicle Emission
- Fuel Pressure. See CHART A-7. Control Information label.
@ Check owner's driving habits. - Ignition wires for cracking, hardness, and proper
- Is A/C "ON" full time (Defroster mode "ON")? connections.
- Are tires at correct pressure? e Check ignition timing. See Emission Control
- Are excessively heavy loads being carried? Information label.
- Is acceleration too much, too often? @ Remove spark plugs. Check for cracks, wear,
- Suggest driver read "Important Facts on Fuel
improper gap, burned electrodes or heavy deposits.
Economy" in owner's manual. Repair
or replace, as necessary.
@ Perform "Diagnostic Circuit Check". @ Check compression. See Section "6A".
@ Check air cleaner element (filter) for dirt or @ Check TCC for proper operation. See CHART C-8.
being plugged. Use "Scan"
tool if available.
@ Check for proper calibration of speedometer. @ Check for dragging brakes.
Suggest owner fill fuel tank and recheck fuel
economy.
@ Check for exhaust system restriction. ,
See CHART B-1.
ROUGH, UNSTABLE, OR INCORRECT IDLE, STALLING
Definition: The engine runs unevenly at idle. If bad enough, the car may
shake. Also,
the idle may vary in rpm (called "hunting"). Either condition
may be severe enough to cause stalling. Engine idles at incorrect speed.
@ CHECK: - Vacuum leaks can cause higher than normal
- Ignition timing. See Emission Control idle.
Information label.
- EGR "ONJ', while idling, will cause roughness,
- PIN switch circuit. See CHART C-1 A. stalling, and hard starting. CHART C-7.
- For injectorb) leaking. Check fuel pressure, - Battery cables and ground straps should be clean ,
CHART A-7. and secure. Erratic voltage will cause IAC to
- IAC - See CHART C-2C.
change its position, resulting in poor idle quality.
- If a sticking throttle shaft or binding linkage - IAC valve will not move, if system voltage is
causes
a high TPS voltage (open throttle
below 9, or greater than 17.8 volts.
indication), the ECM will not control idle.
- Use "Scan" tool to determine if ECM is receiving
Monitor TPS voltage. "Scan"
andlor voltmeter AlC request signal.
should read less than
1.2 volts with throttle
closed.

6E2-8-6 5.OL (VIN E) DRIVEABILITY AND EMISSIONS
- MAP Sensor - Ignition "ON", engine stopped.
Compare MAP voltage with known good vehicle.
-
Voltage should be the same + 400 mV (.4 volts).
OR
Start and idle engine. Disconnect
sensor
electrical connector. If idle improves, substitute
a known good sensor and recheck.
- A/C refrigerant pressure too high. Check for
overcharge or faulty pressure switch.
- PCV valve for proper operation by placing finger
over inlet hole in valve end several times. Valve
should snap back. If not, replace valve.
Run a cylinder compression check See Section
" 6".
Inspect oxygen sensor for silicon contamination
from fuel, or use of improper RTV sealant. The
sensor will have a white, powdery coating, and
will result in a high but false signal voltage (rich
exhaust indication). The ECM will then reduce
the amount of fuel delivered to the engine,
causing a severe driveability problem.
EXCESSIVE EXHAUST EMISSIONS OR ODORS
Definition: Vehicle fails an emission test. Vehicle has excessive "rotten egg"
smell. Excessive odors do not necessarily indicate excessive emissions.
@ Perform "Diagnostic Circuit Check".
@ IF TEST SHOWS EXCESSIVE CO AND HC, (or
also has excessive odors)
@ Check items that will cause engine to run
RICH.
e Make sure engine is at normal operating
temperature.
o CHECK:
- Fuel pressure. See CHART A-7.
- Incorrect timing. See Vehicle Emission
Control Information label.
- Canister for fuel loading. See CHART C-3.
- PCV valve for being plugged, stuck or blocked
PCV hose or fuel in the crankcase.
- Spark plugs, plug wires, and ignition
components. See Section
"6D".
- Check for lead contamination of catalytic
converter (look for removal of fuel filler neck
restrictor).
- Check for properly installed fuel cap.
@ If the system is running rich, (block learn less
than
1181, refer to "Diagnostic Aids" on facing
page of Code
45.
o IF TEST SHOWS EXCESSIVE NOx:
@ Check items which cause car to run LEAN, or
to run too hot.
- EGR valve for not opening. See CHART C-7.
- Vacuum leaks. - Coolant system and coolant fan for proper
operation. See
CHART C-12.
- Remove carbon with top engine cleaner.
Follow instructions on can.
- Check ignition timing for excessive base
advance. See Emission Control Information
label.
@ If the system is running lean, (block learn greater
than
138) refer to "Diagnostic Aids" on facing
page of Code
44.
DIESELING, RUN-ON
Definition: Engine continues to run after key is turned "OFF", but runs very roughly.
Ifengine runs smoothly, check ignition switch and adjustment.
@ Check injector for leaking. Apply 12 volts to fuel Visually check injector and TBI assembly for fuel
pump test terminal to turn "ON" fuel pump and leakage.
pressurize fuel system.
BACKFIRE
Definition: Fuel ignites in intake manifold, making a loud popping noise.
@ CHECK: - For faulty spark plugs and/or plug wires or
- EGR operation for being open all the time. See
hoots.
CHART C-7. - Faulty A.I.R. check valve.
- Output voltage of ignition coil. @ Perform a compression check - look for sticking or
- For crossfire between spark plugs (distributor leaking valves.
cap, spark plug wires, and proper routing' of plug
- For proper valve timing.
wires).
- Broken or worn valve train parts.
- Engine timing - See Emission Control
Information label.

DRIVEABILITY AND EMISSIONS 5.OL (VIN E) 6EZ-B-7
RESTRICTED EXHAUST SYSTEM CHECK
ALL ENGINES
Proper diagnosis for a restricted exhaust system is essential before any components are replaced. Either of
the following procedures may be used for diagnosis, depending upon engine or tool used:
CHECK AT A. I. R. PIPE: - OR CHECK A"F2 SENSOR:
1. Remove the rubber hose at the exhaust 1. Carefully remove O2 sensor.
manifold
A.I.R. pipe check valve. Remove 2. Install Borroughs Exhaust Rackpressure
Tester
(FIT 8515 or BT 8603) or equivalent in
2. Connect a fuel pump pressure gauge to a hose
place of Oz sensor (see illustration).
and nipple from a Propane Enrichment
3. After completing test described below, be
Device
(526911) (see illustration).
sure to coat threads of O2 sensor with anti-
3. Insert the nipple into the exhaust manifold
seize compound PIN 5613695 or equivalent
prior to re-installation.
1. With the engine idling at normal operating temperature, observe the exhaust system backpressure
reading on the gauge. Reading should not exceed
1 t psi (8.6 kPa).
2. Accelerate engine to 2000 RPM and observe gauge. Reading should not exceed 3 psi (20.7 kPa).
3.
If the backpressure, at either RPM, exceeds specification, a restricted exhaust system is indicated.
4. Inspect the entire exhaust system for a collapsed pipe, heat distress, or possible internal muffler failure.
5. If there are no obvious reasons
for the excessive hackpressure, a restricted catalytic converter should be
suspected and replaced using
current recommended proceclures.

6EZ-C-1 5.OL (VIN E) DRIVEABILITY AND EMISSIONS
Section C provides information on the following:
@ General description of components and systems.
@ On-vehicle service.
@ Part names and group numbers.
@ Diagnostic charts. These include a functional check of the system as well as diagnosis of any problem
found in the functional check.
For locations of components, wiring diagrams, and ECM Terminal End View, refer to the front on the A Section
of the engine being diagnosed.
Following are the sub-section identification and the system covered:
@ C1 Electronic Control Module (ECM) and Sensors ............................. Page C1-1
@ C2 Fuel Control System - TBI 200 .......................................... Page C2-1
Evaporative Emission Control System (EECS) ...............................
Ignition System 1 EST ................................................
Electronic Spark Control (ESC) System ...................................
Air Injection Reaction (A.I.R.) System ....................................
Exhaust Gas Recirculation (EGR) System ..................................
Transmission Converter Clutch (TCC) System ..............................
Positive Crankcase Ventilation (PCV) ...................................
Thermostatic Air Cleaner (THERMAC) ...................................
BIAGNOSIIC CHARTS
Page C3-1
Page C4-1
Page C5-1
Page C6-1
Page C7-1
Page C8-1
Page C13-1
Page C14-1
The Diagnostic Charts for each system are found after the on-car service and parts information at the back of
each section. Following are the charts found in this section.
@ Chart C-1A Park Neutral Switch Diagnosis ................................... Page C1-12
@ Chart C-1B Crank Signal ................................................ Page C1-14
@ Chart C-1 D MAP Output Check ........................................ Page C1-16 I
..................... @ Chart C-1 E Power Steering Pressure Switch (PSPS) Diagnosis Page C1-18 1
................................ @ Chart C-2C Idle Air Control (IAC) Valve Check Page C2-16 !
..................................... @ Chart C-3 Canister Purge Valve Check Page C3-4 I
@ Chart C-4 Ignition System Check ......................................... Page C4-4
........................ @ Chart C-5 Electronic Spark Control (ESC) System Check Page C5-4
- ............................. @ Chart C-6 AIR Management Check Pedes Valve Page C6-6
............................. Chart C-7 Exhaust Gas Recirculation (EGR) Check Page C7-4
@ Chart C-8A Transmission Converter Clutch (TCC) Electrical Diagnosis (1 of 2) ......... Page C8-4 I
@ Chart C-8A 700-4R Transmission Electrical Diagnosis (2 of 2) ..................... Page C8-6 I
......................... @ Chart C-8B Manual Transmission Shift Light Diagnosis Page C8-8

DRIVEABILITY AND EMISSIONS 5.OL (VIN El 6EZ-C1-1
SECTION Cl
ELECTWONllC CONTROL MODULE (ECM) AND SENSORS
CONTENTS
GENERAL DESCRIPTION . . . . . . . . . . . . . . . C1-1 Coolant Temperature Sensor . . . . . . . . C1-5
ELECTRONIC CONTROL MODULE (ECM) . . C1-1 MAT Sensor. . . . . . . . . . . .. . . ... . . . . $1 -5
PROM ........................... C1-1 MAP Sensor. . . . . . . . . . . . . . . . . . . . . . C1 -6
CALPAK.........,................ C1-2 Oxygen (02) Sensor. . . . . . ... . . . a C1-6
ECM FUNCTION . . . , . . . . . . . . . . . . . . . . C1-2 Throttle Position Sensor (TPS) . . . . . . . . C1-6
INFORMATION SENSORS . . . . . . . . . . . . . C1-2 Vehicle Speed Sensor (VSS) . . . . . . . . . C1-6
Engine Coolant Temperature Sensor . . C1-2 PIN Switch. . . . . . . . . . . . . . . . . . . . . . . C1-6
MAP Sensor. . . . . . . . . . . . . . . . . . . . . . C1-2 (PSPS) . . . . . ... .. . . . ... . . .. .. . . . C1-6
MAT Sensor. . . . . . . . . . . . . . . . . . . . . . C1-3 AJC Request Signal . . . . . . . . . . . . . . . . C1-6
Oxygen (Oz) Sensor. . . . . . . . . .. . . . . . C1-3 Distributor Reference Signal . . . . . . . . . C1-6
Throttle Posit~on Sensor (TPS) . . . . . . . . C1-3 Knock Signal . . . . . . . . . . . . . . . . . . . C1-6
Knock Sensor . . . . . . . . . . . . . . . . . . . . C1-4 ON-CAR SERVICE . . . . . . . . . . . . . . . . . . . . . C1-6
Park Neutral Switch (Auto Only) . . . . . . C1-4 ELECTRONIC CONTROL MODULE . . . . . . . 61-6
Crank Signal . . . . . . , . . . . . . . . . . . . . . C1-4 PROM ........................... C1-7
A/C "On" Signal . . . , . . . . . . . . . . . . . . C1-4 Functional Check . . . . . . . . . . . . . . . . . C1-8
Vehicle Speed Sensor (VSS) . . . . . . . . . C1-4 CALPAK...................,...... C1-8
Distributor Reference Signal . . . . . . . . . C1-4 COOLANTSENSOR .. . . . . . . . , . . . . . . . . . C1-9
(PSPS) . . . . . . . . . . . . . . . . . . . . . . . . . C1-4 MAPSENSOR ..... ........ ... . .. . .* C1-9
DIAGNOSIS . . . . . . . . . . . . . . . . . . . . . . . . . C1-5 OXYGEN (02) SENSOR . . . . . . . . . a . . a . . C1-9
ECM ............................. C1-5 THROTTLE POSITION SENSOR (TPS) . . . . . C1-10
PROM ........................... C1-5 PARKINEUTRALSWITCH . . . . . . . . . . . . . . C1-10
ECM INPUTS.. . . . . . . . . . . . . . . . , . . . . . C1-5 PARTS
INFORMATION . . . . . . . . . . . . . . . . . C1-10
GENERAL DESCRIPTION
ELECTRONIC CONTROL MODULE (ECM)
The electronic control module (KCMI (Figure C1-
1) is the control center of the fuel ir!jection system. It
constantly looks at the information from various
sensors, and controls the systems that affect vehicle
performance. The ECM performs the diagnostic
function of the system. It can recognize operational
problems, alert the driver through the "Service
Engine Soon" light, and store a code or codes which
identify the problem areas to aid the technician in
making repairs. See "Introduction" for more
information on using the diagnostic function of the
ECM. For service, the ECM has three parts:
a
Controller (the ECM without the PROM), a separate
calibrator (PROM), and a
CALPAK.
To allow one model of ECM to be used for many
different cars, a device called a Calibrator (or PROM)
(Programmable Read Only Memory) is used (see
Figure
C1-2). The PROM is located inside the ECM,
ancl has information on the vehicle's weight, engine,
transmission, axle ratio, and several others. While one
ECM part number can be used by many car lines, a
ECM PROM ACCESS COVER
1 ECM HARNESS
CONNECTORS TO ECM
45 1196-6E
Figure C1-1 Electronic Control Module (ECM) (5.OL)
PROM is very specific and must be used for the right
car. For this reason, it is very important to checlc the
latest parts book and Service Bulletin information for
the correct part number when replacing
a PROM.
An ECM used for service (called a controller)
comes without a
PROM. The PROM from the old blC>1
must be carefully removed and installctl in the new
EChI (see On-Car Service).

6EZ-C1-2 5.OL (VIN E) DRIVEABILITY AND EMISSIONS
PROM CARRIER
PROM (ENGINE CALIBRATOR)
Figure C1-2 - PROM (Calibrator) and CALPAK (5.OL)
CALPAK
ENGINE COOLANT TEMPERATURE SENSOR
HARNESS CONNECTOR TO ECM
LOCKING TAB
4-2-85
*5S 1640-6E
Figure C1-3 - Engine Coolant Temperature Sensor
A device called a CALPAK is used to allow fuel
A failure in the coolant sensor circuit should set
delivery if other parts of the ECM are damaged. It has
either a Code 14 or Code 15. Remember, these codes
an access door in the ECM, and removal and
indicate a failure in the coolant temperature circuit,
replacement procedures are the
same as with a
so proper use of the chart will lead to either repairing
PRO;\/I. a wiring problem or replacing the sensor, to properly
If the CALPAK is missing, it will result in a no
repair a problem.
start
i111d run condition. The CALPAK must be
transferred to a replacement ECM.
MAP Sensor
ECM FUNCTION
The ECM supplies either 5 or 12 volts to power
various sensors or switches. This
is done through
resistances in the ECM which are so high in value
that a test light will not light when connected to the
circuit. In some cases, even an ordinary shop
voltmeter will not give an accurate reading because
its resistance is too low. Therefore, a 10 Meg Ohm
input impedance digital voltlmeter is required to
assure accurate voltage readings.
The ECM controls output circuits such as the
Injector, IAC, Cooling Fan Relay, etc. by controlling
the ground circuit through transistors in the ECM.
INFORMATION SENSORS
Engine Coolant Temperature Sensor
The coolant sensor (Figure C1-3) is a thermistor (a
resistor which changes value based on temperature)
mounted in the engine coolant stream.
[,ow coolant
temperature produces a high resistance
( 100,000 ohms
at
-40°C/-40°F) while high temperature causes low
resistance
(70 ohms at 13O0C/266"F)
The ECM supplies a 5-volt signal to the cooliint
sensor thru a resistor in the ECM and measures the
voltage. The voltage will be high when the engine is
cold,
and low when the engine is hot. By measuring
the voltage, the ECM knows the engine coolant
temperature. Engine coolant temperature affects most
systems the ECM controls. The
manifold absolute pressure
(MAP) sensor
(Figure
(21-4) measures the changes in the intake
manifold pressure which result from engine load and
speed changes, and converts this to a voltage output.
A closed throttle on engine coastdown would
produce a relatively low
MAP output, while a wide-
open throttle would produce a high output. This high
output is produced because the pressure inside the
manifold is the same as outside the manifold, so you
measure 100% of outside air pressure. Manifold
absolute pressure (MAP) is the OPPOSITE of what
you would measure on a vacuum gage.
SENSOR
MANIFOLD VACUUM TUBE
ELECTRICAL CONNECTOR
Figure C1-4 - MAP Sensor

DRIVEABILPTY AND EMISSIONS 5.QL (VIN E) 6E2-C"1-3
MAT SENSOR (TYPICAL)
Figure C1-5 - MAT Sensor - Typical
When manifold pressure is high, vacuum is low. The
MAP
sensor is also used to measure barometric
pressure under certain conditions, which allows the
ECM to automatically adjust for different altitudes.
The ECM sends a 5-volt reference signal to the
MAP sensor. As the manifold pressure changes, the
electrical resistance of the sensor also changes. By
monitoring the sensor output voltage, the ECM knows
the manifold pressure. A higher pressure, low vacuum
(high voltage) requires more fuel, while a lower
pressure, higher vacuum (low voltage) requires less
fuel.
The
ECM uses the MAP sensor to control fuel delivery
and ignition timing.
A failure in the
MAP sensor circuit should set a
Code 33 or Code 34.
Manifold Air Temperature (MAT) Sensor
The manifold air temperature sensor (MAT) is a
thermistor, a resistor which changes value based on
the temperature of air entering the enigne. Low
temperature produces
a high resistance ( 100,000 ohms
at
- 40°C I- 40°F), while high temperature causes low
resistance (70 ohms at 130°C
I 226°F). The ECM
supplies a
5 volt signal to the sensor through a resistor
in the ECM and measures the voltage. The voltage
will be high when the intake air is cold and low when
the air is hot. By measuring the voltage, the ECM
knows the manifold air temperature.
The MAT sensor is also used to control spark
timing and to delay EGR when
intake air is cold.
A failure in the
MAT sensor circuit should set
either a Code 23 or Code 25.
Oxygen (02) Sensor
The exhaust oxygen sensor is mounted in the
exhaust system where it can monitor the
oxygen
content of the exhaust gas stream.
EXHAUST OXYGEN (02)
Figure C1-6 - Exhaust Oxygen (Oz) Sensor
The oxygen content in the exhaust reacts with the
oxygen sensor to produce a voltage output. This
voltage ranges from approximately
.1 volts (high 02 -
lean mixture) to .9 volts (low 02 - rich mixture).
By monitoring the voltage output of the O2 sensor,
the ECM will know what fuel mixture command to
give to the injector (lean mixture
- low voltage - rich
command, rich mixture
- high voltage - lean
command). This voltage can be measured with a
digital voltmeter having at least 10
Meg Ohms input
impedance. Use of standard shop type voltmeters will
result in very inaccurate readings.
'I'he 02 sensor, if open, should set a Code 13. A
shorted sensor circuit should set
a Code 44. A high
voltage in the circuit should set a Code 45. When any
of these codes are set, the car should run in the "Open
Loop" mode.
Throttle Position Sensor (TPS)
The throttle position sensor ('I'PS) is connected to
the throttle shaft on the
TBI unit (see Figure C1-7). It
is a potentiometer with one end connected to 5 volts
from the ECM and the other to ground. A third wire is
connected to the ECM to measure the voltage
from the
TPS. As the throttle valve angle is changed
(accelerator pedal moved), the output of the TPS also
changes. At a closed throttle position, the output of the
TPS is low (approximately
.5 volts). As the throttle
valve opens, the output increases so that, at wide-open
throttle, the output voltage should be approximately
5
volts.
By monitoring the output voltage from the TPS,
the
ECM can determine fuel delivery based on throttle
valve angle (driver
demand).If the sensor CKT is open,
the ECM will set a Trouble Code 22. If the circuit is
shorted, the ECM will think the vehicle is at WOT,
and a Trouble Code 21 will be set.

6EZ-C1-4 S.OL (VIN E) DRIVEABILITY AND EMISSIONS
THROTTLE VALVE
ENGINE CONTROL MODULE (ECM)
THROTTLE POSITION
(TPS)
8P 0321.
Figure C1-7 - Throttle Position Sensor (Typical)
A brolten or loose TPS can cause intermittent bursts of
fuel from the injector, and an unstable idle, because
the ECM thinks the throttle is moving. Once a trouble
code is set, the ECM will use an artificial value for
TPS, and some vehicle performance will return.
On all engines, the TPS is not adjustable. The
ECM uses the reading at idle for the zero reading, so
no adjustment is necessary.
Knock Sensor
The knock sensor is mounted in the engine block.
When abnormal engine vibrations (spark knock) are
present, the sensor produces a voltage signal, which is
sent to the ESC module.
See Section
"C5" for further information on the
electornic spark control
(ESC) system.
ParklNeutral Switch (Auto Only)
The parWneutra1 (PIN) switch indicates to the
ECM when the transmission is in park or neutral.
This information is used for the TCC
, and the IAC
valve operation.
Important
Vehicle should not be driven with parklneutral
switch disconnected as idle quality will be affected
and a possible false Code
24 VSS.
See Section
"8A" for more information on the PIN
switch, which is part of the neutrallstart and
backup light switch assembly.
Crank Signal
The ECM looks at the starter solenoid to tell when
the engine is cranking. It uses this to tell when the car
is in the Starting Mode.
If this signal is not available, car may be hard to
start in extremely cold weather.
AIC Request Signal
This signal tells the ECM that the AJC selector
switch is turned
"ON", and that the pressure cycling
switch is closed. The ECM uses this to adjust the idle
speed when the air conditioning is working.
Vehicle Speed Sensor (VSS)
The vehicle speed sensor (VSS) sends a pulsing
voltage signal to the ECM, which the ECM converts to
miles per hour. This sensor mainly controls the
operation of the TCC system. See "TCC System" for
more information.
Distributor Reference Signal
The distributor sends a signal to the ECM to tell it
both engine rpm and crankshaft position. See "EST
System" for further information.
Power Steering Pressure Switch (PSPS)
I
This switch tells the ECM that the vehicle is in a
parking maneuver.
The ECM uses this information to
compensate for the additional engine load by moving
the IAC valve. The ECM will, also, turn
"OFF" the
A/C clutch when high pressure is detected.
( POWER STEERING PRESSURE SWITCH
Figure C'I-8 - Power Steering Pressure Switch (PSPS)

DRIVEABILITY AND EMISSIONS 5.OL (VIN E) 6EZ-C1-5
DIAGNOSIS
Since the ECM can have a failure which may
effect only one circuit, following the diagnostic
procedures in this section can reliably tell when a
failure has occurred in the ECM. Also,
a Code
55 in
dicates a failure of the ECM.
If a diagnostic chart indicates that the ECM
connections or ECM is the cause of a
problem,and the
ECM is replaced, but does not correct the problem, one
of the following may be the reason:
e
connections. - The diagnostic chart will say "ECM
Connections or ECM". The terminals mav have to be
removed from the connector in order to check them
properly.
@ The ECM or PROM is not correct for the
. - The incorrect ECM or PROM may cause
a malfunction and may or may not set a code.
. - This means that
time the system is
being checked. In this case, refer to the "Symptoms"
portion of the manual and make a careful physical
Solenoids and relays are turned "ON" and "OFF" by
the ECM, using internal electronic switches called
"Drivers".
A shorted solenoid, relay coil, or harness in a
GMP4 computer will not damage the ECM,
but will cause the circuit and controlled
component to be inoperative. When the
circuit fault is not present or has been
repaired, the "Quad-Driver" will again
operate in a normal manner due to it's fault
protected design. If a fault has been repaired
in a circuit controlled
by a "Quad-Driver", the
original
ECM should be reinstalled and the
circuit checked for proper operation.
ECM
replacement will not be necessary if the
repaired circuit or component now operates
correctly.
534636 or BT8405 testers or equivalent provide a
fast, accurate means of checking for a shorted coil or a
short to battery voltage.
e , - Although the
PROM rarely
fails,it operates as part of the ECM.
Therefore, it could be the cause of the problem.
Substitute a known good PROM.
o . - After the
ECM is replaced, the system should be rechecked for
proper operation. If the diagnostic chart again
indicates the ECM is the problem, substitute a known
good ECM. Although this is a rare condition, it could
happen. The
components or circuits and the codes or
charts, related to them are:
@ Code 55 indicates a failure of the ECM.
@ PROM - Code 51.
@ Coolant Temperature Sensor - CHARTS 14 -
15.
@ MAP sensor - CHART 33 or 34. To check the
sensor with no code set, use CHART
C-1D.
e TPS - CHARTS 21 or 22.
e PIN switch - CHART C-1A
@ Crank Signal - CHART C-1B
@ O2 Sensor - CHARTS 13,44,45.
@ VSS - CHART 24 and in TCC System.
e Distributor - CHART 42 and in EST system.
@ Distributor - Chart and in the EST system.
ECM
A faulty ECM will be determined in the diagnostic
charts, or by a Code 55.
PROM
An incorrect or faulty PROM, which is part of the
ECM, may set a Code 51.
ECM INPUTS
All of the sensors and input switches can be
diagnosed by the use of a "Scan" tool. Following is
a
short description of how the sensors and switches can
be diagnosed by the use of "a Scan" tool. The
"Scan"
tool can also by used to compare the values for a
normal running engine with the engine you're
diagnosing.
Coolant Temperature Sensor
A "Scan" tool displays engine temp. in degrees
centigrade. After the engine is started, the
temperature should rise steadily to about
90°C, then
stabilize when thermostat opens.
A fault in the
coolant sensor circuit should set a Code 14 or 15. The
code charts also contain a chart to check for sensor
resistance values relative to temperature.
MAT Sensor
A "Scan" tool displays temperature of the air
entering the engine and should read close ambient air
temperature, when engine is cold, and rise
as
underhood temperature increases. If the engine has
not been run for several hours (overnight), the MAT
sensor temperature and coolant temperature should
read close to each other.