PONTIAC FIERO 1988 Service Repair Manual

DRIVEABILITY AND EMISSIONS . FUEL INJECIION 6E-1
DRBVEABILIW AND EMISSIONS
CONEENTS
General Information . Section 6E
Driveability and Emissions . Fuel Injected (TBI) . Section 6EZ
Driveability and Emissions . Fuel injected (PORT) . Section 6E3
..................... DRIVEABILITY 6E-1
........................ EMISSIONS 6E-1
MAINTENANCE SCHEDULE ............ 6E-1
VEHICLE EMISSIONS CONTROL
............. INFORMATION UBEL 6E-3
.................... INTRODUCTION 6E-3
.......... Electronic Engine Control 6E-3
What This Section Contains .......*. 6E-3
............. Blocking Drive Wheels 6E-3
.............. Cold Oxygen Sensor 6E-3
VISUAUPHYSICAL UNDERWOOD
..................... INSPECTION 6E-3
BASIC KNOWLEDGE REQUIRED ........ 6E-3
.............. Basic Electric Circuits 6E-3
Use of Circuit Testing Tools ......... 6E-4
Use of Digital Volt-Ohm Meter (DVM) . . 6E-4
DIAGNOSTIC INFORMATION .......... 6E-4
"Service Engine Soon" Light ........ 6E-4
Intermit . "Service Engine Soon" Light . . 6E-4
................... Trouble Codes 6E-4
.................. ALDL Connector 6E-4
Diagnostic Mode ................. 6E-4
Field Service Mode ................ 6E-5
............ Clearing Trouble Codes 6E-5
............. ECM Learning Ability 6E-5
DRIVEABILITY AND EMISSIONS ......... 6E-5
SECTIONS 6E2 and 6E3 SUMMARY ...... 6E-5
SECTION A ....................... 6E-6
Diagnostic Procedure Summary ...... 6E-6
ALDL "SCAN" TOOLS ................ 6E-6
Normal (Open) Mode ............. 6E-6
ALDL (1 OK. or Special) Mode ......... 6E-7
Factory Test (Backup or 3.9K) Mode .... 6E-7
DRIVEABILITY
The driveability diagnosis procedures apply to
various systems in current GM vehicles
. The
procedures assume that the vehicle worked right at
one time and the problem is due to time, wear. dirt or
other causes
. Start with the introduction that follows .
This will describe a systematic diagnostic procedure .
Any system disconnected during diagnosis should
be reconnected
. This includes wires, hoses. linkage.
etc . When removing air cleaner. plug hose fittings
that could cause an air leak
.
"SCAN" TOOLS LIMITATIONS AND USE ... 6E-7
Intermittent Conditions ........... 6E-7
"SCAN" TOOL POSITIONS ............ 6E-7
SECTION B . DRIVEABILITY SYMPTOMS . . 6E-10
SECTION C- COMPONENT SYSTEMS ..... 6E-10
Electronic Control Module (ECM) ..... 6E-10
Fuel Control System ............... 6E-10
Electric Fuel Pump (In-tank) ........ 6E-10
....... Evaporative Emission Control 6E-10
Electronic Spark Timing (EST) ....... 6E-10
....... Electronic Spark Control (ESC) 6E-10
Air Injection Reaction (A.I.R.). ........ 6E-10
......... Early Fuel Evaporation (EFE) 6E-10
Exhaust Gas Recirculation (EGR) ...... 6E-11
Transmission Convefler Clutch (TCC) . . 6E-11
.............. Shift Light Control ; . 6E-I I
................ NC Clutch Control 6E-11
........ Electric Cooling Fan Control 6E-11
Positive Crankcase Ventilation (PCV)
...... or Crankcase Ventilation (CV) 6E-11
Thermostatic Air Cleaner (THERMAC) . . 6E-11
ABBREVIATIONS & GLOSSARY OF TERMS .. 6E-1 1
............ WIRING HARNESS SERVICE 6E-14
......................... GENERAL 6E-14
WIREHARNESS.... ............*.... 6E-15
CONNECTORS .....e..e..ee...~.e.. 6E-15
................... Weather-Pack 6E-15
.................. Compact Three 6E-16
Metri-Pack Series 150 . Terrn'l Removal 6E-16
...................... Micro-Pack 6E-16
...... TOOLS NEED TO SERVICE SYSTEM 6E-17
GENERAL SPECIFICATIONS ............. 6E-23
EMISSIONS
The exhaust emission control systems used on
General Motors engines perform a specific function to
lower exhaust emissions while maintaining good fuel
economy and driveability
.
MAINTENANCE SCHEDULE
Refer to the General Motors Maintenance
Schedule in Section
"OB" of the Chassis Service
Manual for the maintenance service that should be
performed to retain emission control performance
.

6E-2 DRIVEABILITY AND EMISSIONS - FUEL INJECTION
"ALWAYS REFER TO THE VEHICLE EMISSION CONTROL INFORMATION LABEL
FOR THE CORRECT AND MOST CURRENT SPECIFICATIONS"
L EVAPORATIVE EMISSION SYSTEM
Figure 1 - Vehicle Emission Control Information Label

DRIVEABILITY AND EMISSIONS - FUEL INJECTION 6E-3
VEHICLE EMISSION CONTROL INFORMATION
MBEL
The Vehicle Emission Control Information label
(Figure
1) contains important emission specifications
and setting procedures. In the upper left corner is
exhaust emission information which identifies the
year, the manufacturing division of the engine, the
displacement in liters of the engine, the class of
vehicle and type of fuel metering. Also there is an
illustrated emission component and vacuum hose
schematic. A similar label is located in the engine
compartment of every General Motors Corporation
vehicle. If the label has been removed, it can be
ordered from the parts division.
(WDDGM)
INTRODUCTION
Electronic Engine Control
Each engine has an electronic engine control
module
(ECM) to control the fuel system. The ECM
varies the
airlfuel ratio by controlling the fuel flow
through the
injectorb).
In addition, the ECM controls the ignition timing
as well as the fuel pump and other systems.
It is important to review the component sections
and wiring diagrams in Section
"6E2" and "6E3" for a
specific engine, to determine what is controlled by the
ECM and what systems are
non-ECM controlled.
What This Section Contains
Each General Motors engine has system controls
to reduce exhaust emissions while maintaining good
driveability and fuel economy. This section explains:
@ Wow to use the Driveability and Emission
Sections
"6E2" for TBI, and "6E3" for Port
Fuel engines.
A brief description of systems used to control
fuel and emissions.
@ Abbreviations that are used in "Driveability
and Emissions".
@ Wiring harness service information for
harnesses used with the ECM.
@ Special tools used to diagnosis and repair a
system. Before
checking the system, observe the following:
Blocking Drive Wheels
The vehicle drive wheels always should be
blocked, and parking brake firmly set, while checking
the system.
Cold Oxygen Sensor
On some engines, the oxygen sensor will cool off
after only a short period of operation at idle. This will
put the system into "Open Loop". To restore "Closed
Loop" operation, run the engine at part throttle and
accelerate from idle to part throttle a few times until
the system goes "Closed Loop".
VlSUAUPHYSlCAL UNDERHOOD
INSPE6"rON
This can often lead to fixing a problem without further
steps. Inspect all vacuum hoses for correct routing,
pinches, cuts, or disconnects. Be sure to inspect hoses
that are difficult to see beneath the air cleaner,
compressor, generator, etc. Inspect all the wires in the
engine compartment for correct and good connections,
burned or chafed spots, pinched wires, or contact with
sharp edges or hot exhaust manifolds. This
visual/physical inspection is very important. It must ,
be done carefully and thoroughly.
BASIC KNOWLEDGE REQUIRED
Before using this section of the service manual,
there are some areas that you should be familiar with.
Without this basic knowledge, you will have trouble
using the diagnostic procedures contained in this
section.
Basic Electric Circuits
You should understand the basic theory of
electricity, and know the meaning of voltage, amps,
ALL NEW GENERAL MOTORS VEHICLES ARE CERTIFIED BY THE UNITED STATES
ENVIRONMENTAL PROTECTION
AGENCY AS CONFORMING TO THE REQUIREMENTS OF THE
REGULATIONS
FOR THE CONTROL OF AIR POLLUTION FROM NEW MOTOR VEHICLES. THlS
CERTIFICATION IS CONTINGENT OM CERTAIN ADJUSTMENTS BEING SET TO FACTORY
STANDARDS. IN MOST CASES, THESE ADJUSTMENT
POINTS EITHER HAVE BEEN
PERMANENTLY SEALED
AND/OR MADE INACCESSIBLE TO PREVENT INDISCRIMINATE OR
ROUTINE ADJUSTMENT IN THE FIELD. FOR
THlS REASON, "TI- FACTORY PROCEDURE FOR
TEMPORARILY REMOVING PLUGS, CAPS, ETC., FOR PURPOSES OF SERVICING THE PRODUCT,
MUST BE STRICTLY FOLLOWED AND, WHEREVER PRACTICABLE, RETURNED
TO WE
ORIGINAL INTENWF THE DESIGN.

6E-4 DRIVEABILITY AND EMISSIONS - FUEL INJECnON
and ohms. You should understand what happens in a
circuit with an open or a shorted wire. You should be
able to read and understand a wiring diagram. A
short to ground
is referred to as a ground to
distinguish it from a short between wires.
Use of Circuit Testing Tools
You should know how to use a test light, how to
connect and use
a tachometer, and how to use jumper
wires to by-pass components to test circuits. Care
should be taken to not deform the terminal when
testing.
Use of Digital Volt-Ohm Meter (DVM)
You should be familiar with the digital volt-ohm
Meter, particularly essential tool J-29125-A,
J34029A
or equivalent. You should be able to measure voltage,
resistance, and current, and know how to use the
meter correctly.
The digital volt-ohm meter is covered in the
"Special
ToolsJ'portion of this section.
DIAGNOSTIC INFORMATION
The electronic control module (ECM) is equipped
with a self-diagnosis system which detects system
failure and aids the technician by identifying the
circuit at fault via a trouble code. Below is
information about the way the ECM displays a
problem and how this corresponds to a trouble code in
the ECM. The ECM can also indicate an "Open Loop"
or "Closed Loop" mode.
"'Service Engine Soonw Light
This light is on the instrument panel, and has two
functions:
@ It is used to tell the driver that a problem has
occurred, and that the vehicle should be taken for
service as soon as reasonably possible.
@ It is used by the technician to read out "Trouble
CodesJ' to help diagnose system problems.
As a bulb and system check, the light will come
"ON" with the key "ON" and the engine not running.
When the engine is started, the light will turn "OFF".
If the light remains "ONJ', the self-diagnostic system
has detected a problem. If the problem goes away, the
light will go out in most cases after 10 seconds, but a
Trouble Code will remain stored in the ECM.
Intermittent "Service Engine Soon" Light
The diagnostic charts in Section "A" are set up to
check whether or not a stored trouble code is
"intermittent" or "hard". An
"intermittent" code is one which does not
always reset when the code setting parameters are
met, or is not present while you are working on the
vehicle. This is often caused by
a loose connection.
The facing page will contain diagnostic aids to help in
detecting
intermittents.
A "hard" code is one which is present when you
are working on the vehicle and the condition still
exists while working on the vehicle. The chart with
the stored trouble code number will lead you to the
cause of the problem.
Trouble Codes
The engine control module (ECM) is really a
computer. It uses sensors to look at many engine
operating conditions. It has
a memory and it knows
what certain sensor readings should be under certain
conditions. These conditions are described on the
facing page of each Trouble Code chart. If a sensor
reading is not what the ECM thinks it should be, the
ECM will turn "ON" the "Service Engine Soon" light
on the instrument panel, and will store a Trouble Code
in the memory. The Trouble Code tells which circuit
the trouble is in. A circuit consists of a sensor (such as
coolant temperature), the wiring and connectors to it,
and the ECM.
i
To get a Trouble Code out of the ECM, we use the
assembly line diagnostic link (ALDL) connector.
!
ALDL Connector I
I
The assembly line diagnostic link (ALDL) is a
diagnostic connector located in the passenger
compartment (Figure 2). It has terminals which are
used in the assembly plant to check that the engine is
operating properly before it leaves the plant.
Terminal "B" is the Diagnostic terminal, and it can be
connected to terminal
"A", or ground, to enter the
Diagnostic mode, or the Field Service Mode.
The ALDL connector is also used by "ScanJ' tools to
read information from the ECM via the Serial Data
Line. Serial Data information
is used extensively
throughout the manual.
Diagnostic Mode
1
If the Diagnostic terminal is grounded with the
ignition "ON" and the engine stopped, the system will
enter the Diagnostic Mode. In this mode the ECM
will:
1. Display a Code 12 by flashing the "Service Engine
Soon" light (indicating the system is operating). A
Code 12 consists of one flash, followed by a short
pause, then two flashes in quick succession. This
code will be flashed three times. If no other codes

DRIVEABILITY AND EMISSIONS - FUEL INJECTION 6E-5
TERMINAL IDENTIFICATION
GROUND SERIALDATA
(SEE SPECIAL TOOLS)
DIAGNOSTIC TERMINAL
I.I.R. (IF USED) T.C.C. (IF USED)
SERVICE
ENGINE FUEL PUMP (IF USED)
SOON LAMP- IF USED
SERIAL DATA (IF USED) 3-29-86 *6S 2615-6E (SEE SPECIAL TOOLS)
Figure 2 - ALDL Connector
are stored, Code 12 will continue to flash until the
Diagnostic terminal is ungrounded.
Codes can only be obtained with the engine
stopped. Grounding the Diagnostic terminal with the
engine running gives the "field service mode".
2. Display any stored trouble codes by flashing the
"Service Engine Soon" light. Each code will be
flashed three times, then Code
12 will be flashed
again.
If a trouble code is displayed, the memory is
cleared, then the engine is run to see
if the code is
a "hard" or "intermittent" failure. If it is a "hard"
failure, a Diagnostic Code chart is used to find the
problem. If it is an intermittent failure, the charts
are not used. Diagnostic aids are usually included
on the facing page. Section
"B" also covers the
topic of "Intermittents".
A physical inspection of
the applicable system most often will resolve the
problem.
3. Energize all ECM controlled relays and solenoids
except fuel pump relay
.
4. The IAC valve on most models also moves to the
fully extended position.
Field Service Mode
If the Diagnostic terminal is grounded with the
engine running, the system will enter the Field
Service mode. In this mode, the "Service Engine
Soon" light will show whether the system is in "Open"
or
"Closed Loop".
In "Open Loop" the "Service Engine Soon" light
flashes two and one-half times per second.
In "Closed Loop", the light flashes once per second:
Also, in "Closed Loop", the light will stay OUT most of
the time
if the system is too lean. It will stay "ON"
most of the time if the system is too rich.
While the system is in Field Service Mode, the
ECM will be in the following mode:
1. New trouble codes cannot be stored in the ECM.
2. The "Closed Loop" timer is bypassed.
Clearing Trouble Codes
When the ECM sets a trouble code, the "Service
Engine Soon" light will come "ON" and a trouble code
will be stored in memory. If the problem is
intermittent, the light will go out
10 seconds after the
fault goes away. However, the trouble code will stay
in the ECM memory until the battery voltage to the
ECM is removed. Removing battery voltage for
30
seconds will clear all stored trouble codes.
Trouble Codes should be cleared after repairs have
been completed. Also, some diagnostic charts will tell
you to clear the codes before using the chart. This
allows the ECM to set the code while going thru the
chart, which will help to find the cause of the problem
more quickly.
NOTICE: To prevent ECM damage, the key must
be
"OFFn when disconnecting or
reconnecting power to
ECM (for
example battery cable,
ECM pigtail,
ECM fuse, jumper cables, etc.).
ECM Learning Ability
The ECM has a "learning" ability which allows it
to make corrections for minor variations in the fuel
system to improve driveability. If the battery is
disconnected to clear diagnostic codes, or for repair,
the "learning" process has to begin all over again.
A
change may be noted in the vehicle's performance. To
"teach" the vehicle, make sure the engine is at
operating temperature, and drive at part throttle,
with moderate acceleration and idle conditions, until
normal performance returns.
DRIVEABILITY AND EMISSIONS
SECTIONS
6E2 and 6E3 SUMMARY
The Driveability and Emissions sections are
subdivided into three sub-sections:
SECTION A: STARTING POINT AND CODE CHARTS
@ Diagnostic circuit check (Starting Point)
@ No-start and fuel system check charts
@ Code Charts
SECTION B: SYMPTOMS
e Based on driveability symptoms, when no
codes, or intermittent codes, are stored.
SECTION C: COMPONENT SYSTEMS
@ Circuit descriptions
@ On-car service
@ Functional checWDiagnosis charts

6E-6 DRIVEABILITY AND EMISSIONS - FUEL INJECTION
SECTION A
Diagnostic Procedure Summary
diagnostic charts are related to the ECM and will
determine if the ECM is working properly. This
section diagnoses the fuel system controlled by the
ECM and has charts to diagnose a circuit when the
ECM has displayed a trouble code.
The way
to approach a problem is to follow three
basic steps (shown in Figure
3):
1. We find
this out by performing the "Diagnostic Circuit
If the On-Vehicle Diagnostics aren't working, the
"Diagnostic Circuit Check" will lead you to a chart
in Section
"A" to correct the problem. If the On-
Vehicle Diagnostics are OM, the next step is:
2. Is there a Trouble Code stored? If a trouble code is
stored, go directly to the numbered code chart in
Section
"A". This will determine if the fault is
still present. If no trouble code is stored, then:
3. "Scan" Serial Data.
This involves reading the various pieces of
information available on the Serial Data Stream
with one of the tools available for that purpose.
Information on these tools and the meaning of the
various displays can be found in the succeeding
paragraphs. Expected readings can be found on
the facing page for the Diagnostic Circuit Check.
This short procedure will help lead you to repair
the problem in the least amount of time.
ALDL "SCAN" TOOLS
The AEDL connector under the dash has a variety
of information available on terminal "E" or
"M"
(depending on engine). There are several tools on the
market for reading this information.
"Scan" tools do not make the use of diagnostic
charts unnecessary. They do not tell exactly where a
problem is in a given circuit. However, with an
understanding of what each position on the equipment
measures, and knowledge of the circuit involved, the
tools can be very useful in getting information which
would be more time consuming to get with other
equipment. In some cases, "Scan" tools will provide
information that is either extremely difficult or
impossible to get with other equipment.
A "SCAN" POOL THAT DISPLAYS FAULTY DATA
SHOULD NOT BE USED AND THE PROBLEM SHOULD
BE REPORTED PO THE MANUFACTURER. THE USE OF
A FAULTY "SCAM'YVOOL CAN RESULT IN
,-d ,--,,,-,,
I SEE CHART A-2 I L----------d
l"d -------- 1 SEE CHART A-2 ----------
r-J--S...-S-- 1
: SEE CHART A-3 j ----------
Figure 3 - Diagnostic Procedure Summary
MISDIAGNOSIS
AND UNNECESSARY PARTS
REPMCEMENT.
I
Trouble Tree Charts incorporate diagnosis
procedures using an ALDL "Scan" tool where possible.
Most charts require use of a "Scan" tool when
it is
applicable. Unless instructed otherwise, code charts
in
"6E" Section "A" should not be used for diagnosis
unless the fault is still present (a "hard" failure).
Some
ECM's have three modes for transmitting
information but some only read data in the open mode.
The following information will describe each of
the three modes where applicable and the effects they
may cause.
Not all engines and ECM families will transmit
information on the Serial Data Line while in this
mode.

DRIVEABILITY AND EMISSIONS - FUEL INJECTION 6E-7
On engines that can be monitored in the open
mode, it allows certain parameters to be obtained
without changing the engine operating
characteristics. The parameters capable of being read
vary from engine family to engine family. Most
"Scan" tools are programmed so that the system will
go directly into the special mode
if the "open" mode is
not available.
ALDL (7 OK, or Special) Mode
(not used on
all engines)
In this mode, all information incorporated into a
specific
engine and ECM is obtainable. However, in
this mode the system operating characteristics are
modified as follows.
@ "Closed Loop" timers are bypassed
EST (spark) is advanced
@ IAC will control engine idle to 1000 rpm I
50 rpm (if applicable)
@ On some engines, canister purge solenoid will
be enabled
@ P/N restrict functions will be disabled.
Factory Test (Back-up or 3.9 K) Mode
(TBI, Port)
In this mode, the ECM is operating on the fuel
back-up logic and is calibrated by the Calpak or Mem-
cal. These are used to control the fuel delivery
if the
ECM fails. This mode verifies that the back-up feature
is OK. The parameters that can be read on a
"Scan"
tool in this mode are not of much use for service.
"SCAN" TOOL LIMITATIONS AND USE
The "Scan" tool allows a quick check of sensors
and switches which are inputs to the ECM. However,
on some applications the data update rate makes the
tool less effective as a voltmeter when trying to detect
an intermittent which lasts for a very short time.
However, the "Scan" tool allows one to manipulate
wiring harnesses or components under the hood while
observing the "Scan" readout. This helps in locating
intermittents with the engine not running.
intermittent Conditions
for a period of time to see if there is any change in the
readings that indicates intermittent operation.
The "Scan" tool is also a useful and quick way of
comparing operating parameters of a poorly operating
engine with a known good one. For example;
A sensor
may shift in value but not set a code. Comparing with
a known good vehicle may uncover the problem.
The "Scan" tool has the ability to save time in
diagnosis and prevent the replacement of good parts.
The key to using the "Scan" tool successfully for
diagnosis lies in the technician's ability to understand
the system he is trying to diagnose as well as an
understanding of the "Scan" tool's limitations.
Therefore, the technician should read the tool
manufacturer's operating manual to become familiar
with the operation. The following information will
describe most of the "Scan" tool positions and how
they can be helpful in diagnosis.
"SCAN" TOOL POSITIONS
The following positions may not be applicable to
all engines. See the facing page
of the diagnostic
circuit check for a particular engine to decide which
positions apply to that engine.
Mode
Check with the manufacturer to determine what
the function of this mode is. In most cases it allows the
user to place the ECM in different operating modes.
Injector Pulse Width
In this position, the reading is given in
milliseconds, which is the
"ON" time that the ECM is
commanding to the
injector(s1.
Closed LoopIOpen Loop
This position will indicate whether the engine
control system is operating in "Open Loop" or "Closed
Loop". Most systems go "Closed Loop" after a certain
amount of running time, when coolant temperature is
high enough, and the oxygen sensor becomes active.
Exhaust (RichILean Indicator)
The "Scan" tool is helpful in cases of intermittent
This indicates the O2 sensor voltage at the instant operation' The can be in and observed that the data stream is sampled. If voltage is less than
while driving the vehicle under the condition where
350 mv, the value will be lean. If above 550 mv, a rich the light comes "ON" momentarily, or the engine exhaust is indicated. driveability is poor momentarily. If the problem
seems to be related to certain areas that can be
Codes checked on the "Scan" tool, then those are the
positions that should be checked while driving the
This will display any trouble codes stored in the
vehicle. If there does not seem to be any correlation
ECM memory. between the problem and any specific circuit, the
"Scan" tool can be checked on each position, watching

6E-8 DRIVEABILITY AND EMISSIONS - FUEL INJECTION
Throttle Position Sensor (TPO) Coolant Q~erature
Values read will be the voltage as seen by the Engine
temperature is displayed in Celsius
ECM. The voltage should be the TPS specification degrees.
After the engine is started, temperature
with the throttle closed and go up to about 5 volts should
rise steadily to about
85-95" C, then stabilize
with throttle wide open
(WOT). when the thermostat opens.
Throttle Angle
Displayed, in percent, is the amount the throttle is
open. 0% is closed throttle, 100% is wide open throttle.
Oxygen (Of) Sensor
The reading will be read out in millivolts (mv)
with a range from 1 to 999 mv. If the reading is
consistently below 350 (350 mv), the fuel system
is
running lean as seen by the ECM; and if the reading is
consistently above 550 (550 mv), the system is
running rich.
In this position, information is used for assembly
verification only. PROM ID is useful only when the
vehicle
is equipped with the original ECM and PROM
or Mem-Cal.
Reading displays engine rpm. It is often useful if
extra reference pulses are suspected. A sudden high
rpm indication while at a steady throttle would
indicate electrical interference
(EMI) in the reference
circuit. This interference
is usually caused by ECM
wires too close to ignition secondary wires or an open
distributor ground circuit.
Displayed is vehicle speed, useful in checking TCC
application speed or speedometer accuracy.
MAF
This displays the amount of air passing the Mass
Air Flow
(MAF) sensor, in grams per second. It is
useful when comparing the airflow between a problem
vehicle and a known good one. Normal readings at
idle are about
4 to 8 grams. If a MAF code is set, this
reading will display the ECM default value.
This display should be the same as MAF when
there are no failures in the MAP sensor circuit. When
an MAF code is set, however, this value will not
change, and will indicate the
grn/sec that the failure
has detected.
Manifold Air Temperature (MAT) Sensor
This displays temperature of the intake manifold
air. It should read close to ambient air temperature
when the engine is cold, and rise as underhood and
engine temperatures increase.
Manifold Absolute Pressure (MAP)
The MAP sensor produces a low signal voltage
when manifold pressure is low (high vacuum) and a
high voltage when the pressure is high (low vacuum).
With the ignition "ON" and the engine stopped,
I
the manifold pressure is equal to atmospheric
pressure, and the signal voltage will be high. This 1
information is used by the ECM as an indication of
vehicle altitude and is referred to as BARO.
Comparison of this
BARO reading with a known good
vehicle with the same sensor is a good way to check
accuracy of a "suspect" sensor
*. Readings should be
the same
+ .4 volt. I
* A MAP sensor has a colored plastic insert visible I I
in the connector cavity. Sensors with the same insert I
color are identical in calibration. The harness I
I
electrical connector color also should be the same as 1 the sensor insert color.
I Vacuum (Differential Pressure) Sensor
The vacuum sensor produces a low signal voltage
when manifold vacuum is low, and a high voltage
when the vacuum is high.
With the ignition "ON" and the engine stopped,
there is no vacuum, so the voltage is low (under
1
volt). With the engine idling the vacuum is high so the
voltage is high (over
3 volts).
A vacuum sensor has a colored plastic insert
visible in the connector cavity. Sensors with the same
insert color are identical in calibration. The harness
electrical connector color also should be the same as
the sensor insert color.
This displays barometric pressure. The ECM uses
this information to adjust for altitude and pressure.
This value will vary depending on barometric
pressure and altitude. Some vehicles use a dedicated
bar0 sensor, while others take a MAP reading before
the engine is started, and at various times during
engine operation.

DRIVEABILITY AND EMISSIONS - FUEL INJECTION 6E-9
ParWNelatral Switch IAC (Idle Air Control)
The indication in this mode may vary with This system is used to control engine idle speed to
manufacturer so the type of reading for a particular the desired rpm, for different operating conditions. In
tool should be checked in the operator's manual. The this mode, the numbers will indicate the position to
important thing is that the the reading changes state which
the ECM has moved the valve pintle. The ECM
(switches) when the gear selector is moved from moves
the IAC in counts, or steps, and the number of
paridneutral to drive or reverse. these counts are displayed on a "Scan" tool.
"Trque Convertor Clutch (TCC)
In this position, the tool will indicate when the
TCC has been commanded by the ECM to turn "ONJ'.
This does not necessarily mean that the clutch was
engaged but only that the
ECM grounded the circuit
internally. The best way to determine if the clutch has
engaged is to monitor engine rpm when the TCC
comes "ON".
EGR (Duty Cycle)
The EGR system uses a valve to feed a small
amount of exhaust gas back into the intake manifold
to control formation of NO,. Like all ECM outputs, the
"Scan" tool only indicates that the ECM has
commanded the function, and does not indicate that
the function has really happened.
EGR Position
This indicates the position of the EGR pintle.
Integrator and Block Learn
Normal readings for these positions are around
128. If higher, it indicates that the ECM is adding fuel
to the base fuel calculation because the system is lean,
and if the numbers are below 128, the ECM is taking
out fuel from the base calculation because the system
is rich. The integrator gives short term corrective
action, while the block learn portion (which is a long
term correction) will only change if the integrator has
seen a condition which lasts for a calibrated period of
time.
Block Learn Multiplier (BLM) Cell - or -
Block Learn Memory (BLM)
There are up to sixteen different cells,
corresponding to ranges of rpm and engine load
(indicated by MAF or MAP signals), and other
conditions, such as
A/C or P/N switch "ON" or "OFF",
etc. The ECM learns how much adjustment is needed
in each cell, and retains it in memory, so that the
adjustment will immediately be made when the
engine operates in that cell (or
rpmlload range). This
parameter will display what cell the ECM is currently
using for the fuel calculation.
Desired RPM
This indicates the rpm to which the ECM is trying
to control the idle.
Shift Light
This displays "yes" when the ECM is commanding
the shift light to turn "ON".
PPSW (Pump Prime Switch)
This is the voltage on the fuel pump feed circuit.
The ECM will adjust fuel injector base pulse width
from this voltage value rather than from battery
voltage.
NC Request
The state of the A/C signal line to the ECM is
shown. It should read "yes" whenever the
IVC is
requested.
NC Clutch
"ON" is displayed when the ECM has commanded
the
A/C clutch "ON".
Knock Retard
This indicates the number of degrees the ECM is
retarding the electronic spark timing (EST).
Knock Signal
This displays a "yes" when knock is detected by
the ECM, and a "no" when knock is not detected.
Battery Voltage
This displays the battery voltage detected at the
ECM ignition input.
Fan
"ON" is displayed when the cooling fan has been
commanded "ON".