power ISUZU TF SERIES 2004 Workshop Manual

6E–4 ENGINE DRIVEABILITY AND EMISSIONS
DIAGNOSTIC TROUBLE CODE (DTC) P0443
EVAPORATIVE (EVAP) EMISSION CONTROL
SYSTEM PURGE CONTROL CIRCUIT ..... 6E-191
Circuit Description ..................................... 6E-191
Diagnostic Aids .......................................... 6E-191
Diagnostic Trouble Code (DTC) P0443
EVAP Emission Control System Purge
Control Circuit .......................................... 6E-192
DIAGNOSTIC TROUBLE CODE (DTC) P0502
VEHICLE SPEED SENSOR (VSS) CIRCUIT
LOW INPUT ................................................ 6E-195
Circuit Description ..................................... 6E-195
Diagnostic Aids .......................................... 6E-195
Diagnostic Trouble Code (DTC) P0502
Vehicle Speed Sensor Circuit Low Input . 6E-196
DIAGNOSTIC TROUBLE CODE (DTC) P0562
SYSTEM VOLTAGE LOW .......................... 6E-202
Circuit Description ..................................... 6E-202
Diagnostic Aids .......................................... 6E-202
Diagnostic Trouble Code (DTC) P0562 System
Voltage Low ............................................. 6E-202
DIAGNOSTIC TROUBLE CODE (DTC) P0563
SYSTEM VOLTAGE HIGH ......................... 6E-204
Circuit Description ..................................... 6E-204
Diagnostic Aids .......................................... 6E-204
Diagnostic Trouble Code (DTC) P0563 System
Voltage High ............................................ 6E-204
DIAGNOSTIC TROUBLE CODE (DTC) P0601
ECM MEMORY CHECKSUM ..................... 6E-206
Circuit Description ..................................... 6E-206
Diagnostic Aids .......................................... 6E-206
Diagnostic Trouble Code (DTC) P0601 ECM
Memory Checksum .................................. 6E-206
DIAGNOSTIC TROUBLE CODE (DTC) P0602
ECU PROGRAMMING ERROR ................. 6E-207
Circuit Description ..................................... 6E-207
Diagnostic Aids .......................................... 6E-207
Diagnostic Trouble Code (DTC) P0602 ECU
Programming Error .................................. 6E-207
DTC P0650 MALFUNCTION INDICATOR LAMP
(MIL) CONTOROL CIRCUIT MALFUNCTION 6E-208
Circuit Description ..................................... 6E-208
Diagnostic Aids .......................................... 6E-208
Diagnostic Trouble Code (DTC) P0650
Malfunction Indicator Lamp (MIL) Control
Circuit Malfunction ................................... 6E-209
DIAGNOSTIC TROUBLE CODE (DTC) P1167
FUEL SUPPLY SYSTEM RICH DURING
DECELERATION FUEL CUT OFF ............. 6E-211
Circuit Description ..................................... 6E-211
Diagnostic Aids .......................................... 6E-211
Diagnostic Trouble Code (DTC) P1167 Fuel Supply System Rich During
Deceleration Fuel Cutoff .......................... 6E-212
DIAGNOSTIC TROUBLE CODE (DTC) P1171
FUEL SUPPLY SYSTEM LEAN DURING
POWER ENRICHMENT ............................. 6E-214
Circuit Description ...................................... 6E-214
Diagnostic Aids .......................................... 6E-215
Diagnostic Trouble Code (DTC) P1171
Fuel Supply System Lean During Power
Enrichment .............................................. 6E-215
DIAGNOSTIC TROUBLE CODE (DTC) P1625
ECM SYSTEM RESET ............................... 6E-217
Circuit Description ...................................... 6E-217
Diagnostic Aids .......................................... 6E-217
Diagnostic Trouble Code (DTC) P1625 ECM
System Reset .......................................... 6E-217
DIAGNOSTIC TROUBLE CODE (DTC) P1626
IMMOBILIZER NO SIGNAL ........................ 6E-218
Circuit Description ...................................... 6E-218
Diagnostic Aids .......................................... 6E-218
Diagnostic Trouble Code (DTC) P1626
Immobilizer No Signal .............................. 6E-219
DIAGNOSTIC TROUBLE CODE (DTC) P1631
IMMOBILIZER WRONG SIGNAL ............... 6E-222
Circuit Description ...................................... 6E-222
Diagnostic Aids .......................................... 6E-222
Diagnostic Trouble Code (DTC) P1631
Immobilizer Wrong Signal ........................ 6E-223
DIAGNOSTIC TROUBLE CODE (DTC) P1648
WRONG SECURITY CODE ENTERED .. 6E-224
Circuit Description ...................................... 6E-224
Diagnostic Aids .......................................... 6E-224
Diagnostic Trouble Code (DTC) P1648 Wrong
Security Code Entered ............................ 6E-225
DIAGNOSTIC TROUBLE CODE (DTC) P1649
IMMOBILIZER FUNCTION NOT
PROGRAMMED ......................................... 6E-226
Circuit Description ...................................... 6E-226
Diagnostic Aids .......................................... 6E-226
Diagnostic Trouble Code (DTC) P1649
Immobilizer Function Not Programmed ... 6E-227
DIAGNOSTIC TROUBLE CODE (DTC) P1693
TACHOMETER OUTPUT LOW VOLTAGE 6E-228
Circuit Description ...................................... 6E-228
Diagnostic Aids .......................................... 6E-228
Diagnostic Trouble Code (DTC) P1693
Tachometer Output Low Voltage ............. 6E-229
SYMPTOM DIAGNOSIS ............................... 6E-232
PRELIMINARY CHECKS ............................. 6E-232
VISUAL/PHYSICAL CHECK ......................... 6E-232
INTERMITTENT ........................................... 6E-232

ENGINE DRIVEABILITY AND EMISSIONS 6E–5
ENGINE CRANKS BUT WILL NOT RUN ..... 6E-233
HARD START SYMPTOM ............................ 6E-236
ROUGH, UNSTABLE, OR INCORRECT IDLE,
STALLING SYMPTOM ............................... 6E-239
SURGES AND/OR CHUGS SYMPTOM ...... 6E-242
HESITATION, SAG, STUMBLE SYMPTOM 6E-245
CUTS OUT, MISSES SYMPTOM ................. 6E-248
LACK OF POWER, SLUGGISH OR SPONGY
SYMPTOM ................................................. 6E-251
DETONATION/SPARK KNOCK SYMPTOM 6E-254
POOR FUEL ECONOMY SYMPTOM .......... 6E-256
EXCESSIVE EXHAUST EMISSIONS OR
ODORS SYMPTOM ................................... 6E-258
DIESELING, RUN-ON SYMPTOM ............... 6E-261
BACKFIRE SYMPTOM ................................. 6E-262
ON-VEHICLE SERVICE PROCEDURE ....... 6E-264
ENGINE CONTROL MODULE (ECM) .......... 6E-264
CRANKSHAFT POSITION (CKP) SENSOR 6E-264
ENGINE COOLANT TEMPERATURE (ECT)
SENSOR .................................................... 6E-265
INTAKE AIR TEMPERATURE (IAT) SENSOR 6E-265
MANIFOLD ABSOLUTE PRESSURE (MAP)
SENSOR .................................................... 6E-266
THROTTLE POSITION SENSOR (TPS) ...... 6E-266
IDLE AIR CONTROL (IAC) VALVE .............. 6E-267
KNOCK SENSOR ......................................... 6E-268
POWER STEERING PRESSURE (PSP)
SWITCH ..................................................... 6E-268
HEATED OXYGEN SENSOR (HO2S) ......... 6E-269
EVAP CANISTER PURGE VALVE SOLENOID 6E-269
FUEL PRESSURE RELIEF .......................... 6E-270
FUEL RAIL ASSEMBLY ............................... 6E-270
FUEL INJECTOR .......................................... 6E-271
FUEL PRESSURE REGULATOR ................ 6E-273
IGNITION COIL ............................................ 6E-275
SPARK PLUGS ............................................ 6E-275
SPARK PLUG CABLES ................................ 6E-277
EMISSION CONTROL ; CO ADJUSTER (W/O
CATALYSTIC CONVERTER) .................. 6E-277
SPECIAL SERVICE TOOLS ......................... 6E-279

6E–10 ENGINE DRIVEABILITY AND EMISSIONS
(1) Canister(1)
(2)Fuel Tank
Fuel Pump
2 1
(1)
(2)Vehicle Speed Sensor (VSS)
Transmission Assembly
12
(1)
(2)Power Steering Pressure Switch
Power Steering Oil Pump Assembly
12

6E–32 ENGINE DRIVEABILITY AND EMISSIONS
FUSE A ND RELAY LOCATION (LHD & RHD)
FUSE
SLOW BLOW FUSE
RELAYNo. Capacity Indication on label No. Capacity Indication on label
1——12 15A CIGER
2 10A ABS 13 15A AUDIO (+B)
3 10A TRAILER 14 20A DOOR LOCK
4 15A BACK UP 15 10A METER (+B)
5 15A METER 16 10A ROOM
6 10A TURN 17 10A ANTI THEFT
7 15A ELEC.IG 18 15A STOP
8 15A ENGINE 19 15A ACC SOCKET
9 20A FRT WIPER 20 10A STARTER
10 15A EGR 21 10A SRS
11 10A AUDIO
No. Capacity Indication on label
22 20A RR DEF
23 30A POWER WINDOW
Connector No. B-7 B-8 B-40
C24SE REAR DEFOGGER POWER WINDOW ACC SOCKET
FUSE BOX

ENGINE DRIVEABILITY AND EMISSIONS 6E–43
J1-21 J1-21 Crankshaft Position
(CKP) Se nsor Signa lWHT - - Wave form
or approx.
3.7VWa v e f o r m
A o r
approx.
7.8VCo nnect AC V J1-21 J1-6
J1-22 J1-22 No.2 Injecto r GRN/
WH TLess tha n
1VWav e fo rm E o r 12-14V Co nnect DC V J1-22 GND
J1-23 J1-23 No Connection - - - - - - - - -
J1-24 J1-24 MAP Sensor Signal GRY Less than
1VApprox.
4.8VApprox.
1.3VApprox.
0.9VCo nnect DC V J1-24 J1-16
J1-25 J1-25 No Connection - - - - - - - - -
J1-26 J1-26 No Connection - - - - - - - J1-26 -
J1-27 J1-27 Engine Coo la nt Temp.
(ECT) Se nsor Signa lGRY Less tha n
1V
20
: Approx. 2.4V / 40
: Approx . 1.4V or
4.1V / 60
: Approx . 3.3V / 80
: Approx .
2.5VCo nnect DC V J1-27 J1-32
J1-28 J1-28 Idle Air Contro l Va lv e
(IACV) Co il A HighBLU Less tha n
1VLess than 1V / 10-14V Connect DC V J1-28 GND
J1-29 J1-29 Idle Air Contro l Va lv e
(IACV) Co il B LowBLU/
BLKLess tha n
1VLess than 1V / 10-14V Connect DC V J1-29 GND
J1-30 J1-30 Idle Air Contro l Va lv e
(IACV) Co il A LowBLU/
WH TLess tha n
1VLess than 1V / 10-14V Connect DC V J1-30 GND
J1-31 J1-31 MAP Sensor Power
SupplyRED Less tha n
1VAppro x.. 5V Co nnect DC V J1-31 J1-16
J1-32 J1-32 ECT Sensor, Knock
Se nsor, Thro ttle
Po sitio n Senso r GroundGRN Continuity
with
gro und- - - Connect
J1-32 GND Pin
No. B/
Box
No.P in FunctionWire
ColorSignal or Continuity
ECM
ConnectionTester Position
Key SW
OffKey SW
OnEngine
IdleEngine
2000rpmRange (+) (-)

6E–48 ENGINE DRIVEABILITY AND EMISSIONS
GENERAL DESCRIPTION FOR ECM AND
SENSORS
Engine Control Module (ECM)
The engine control module (ECM) is located on the
intake manifold. The ECM controls the following.
Fuel metering system
Ignition timing
On-board diagnostics for electrical functions.
The ECM constantly observes the information from vari-
ous sensors. The ECM controls the systems that affect
vehicle performance. And it performs the diagnostic
function of the system.
The function can recognize operational problems, and
warn to the driver through the check engine lamp, and
store diagnostic trouble code (DTC). DTCs identify the
problem areas to aid the technician in marking repairs.
The input / output devices in the ECM include analog to
digital converts, signal buffers, counters and drivers.
The ECM controls most components with electronic
switches which complete a ground circuit when turned
on.
Inputs (Operating condition read):
Battery voltage
Electrical ignition
Ex haust oxygen content
Intake manifold pressure
Intake air temperature
Engine coolant temperature
Crankshaft positionKnock signal
Throttle position
Vehicle speed
Power steering pressure
Air conditioning request on or off
Outputs (Systems controlled):
Ignition control
Fuel control
Idle air control
Fuel pump
EVAP canister purge
Air conditioning
Diagnostics functions
Manifold Absolute Pressure (MAP) Sensor
The MAP sensor is a strain gage. A pressure strains the
resistance on the silicon base. At that time the
resistance value changes. And it changes voltage. In
other words it measures a pressure value. It is installed
to the intake manifold. Output voltage of the MAP
sensor is low as pressure is low. (1) J1 Port
(2) J2 Port
12
C h arac teris tic of MA P S ens or -R ef erenc e-
0 0.51 1.52 2.53 3.54 4.55
15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105
Mani fold A bs olute P res s ure (K P a) (T ec h2 Reading)
Output Voltage (V)

ENGINE DRIVEABILITY AND EMISSIONS 6E–49
Throttle Position Sensor (TPS)
The TPS is a potentiometer connected to throttle shaft
on the throttle body.
The engine control module (ECM) monitors the voltage
on the signal line and calculates throttle position. As the
throttle valve angle is changed when accelerator pedal
moved. The TPS signal also changed at a moved
throttle valve. As the throttle valve opens, the output
increases so that the output voltage should be high.
The throttle body has a throttle plate to control the
amount of the air delivered to the engine.
Engine coolant is directed through a coolant cavity in
the throttle body to warm the throttle valve and to
prevent icing.
Idle Air Control (IAC) Valve
The idle air control valve (IAC) valve is two directional
and gives 2-way control. With power supply to the coils
controlled steps by the engine control module (ECM),
the IAC valve's pintle is moved to adjust idle speed,
raising it for fast idle when cold or there is ex tra load
from the air conditioning or power steering.
By moving the pintle in (to decrease air flow) or out (to
increase air flow), a controlled amount of the air can
move around the throttle plate. If the engine speed is
too low, the engine control module (ECM) will retract the
IAC pintle, resulting in more air moving past the throttle
plate to increase the engine speed.
If the engine speed is too high, the engine control
module (ECM) will ex tend the IAC pintle, allowing less
air to move past the throttle plate, decreasing the
engine speed.
The IAC pintle valve moves in small step called counts.
During idle, the proper position of the IAC pintle is
calculated by the engine control module (ECM) based
on battery voltage, coolant temperature, engine load,
and engine speed.
If the engine speed drops below a specified value, and
the throttle plate is closed, the engine control module
(ECM) senses a near-stall condition. The engine control
module (ECM) will then calculate a new IAC pintle valve
position to prevent stalls.
If the IAC valve is disconnected and reconnected with
the engine running, the idle speed will be wrong. In this
case, the IAC must be reset. The IAC resets when the
key is cycled “On” then “Off”. When servicing the IAC, it
should only be disconnected or connected with the
ignition “Off”.
The position of the IAC pintle valve affects engine start-
up and the idle characteristic of the vehicle.
If the IAC pintle is fully open, too much air will be
allowed into the manifold. This results in high idle
speed, along with possible hard starting and lean air/
fuel ratio. (1) Throttle Position Sensor
(2) Idle Air Control (IAC) Valve
1
2
C haract erist ic of TPS -R ef erenc e-
0 0. 51 1. 52 2. 53 3. 54 4. 55
0 102030405060708090100
Th rot t le An gle ( % ) ( Tec h 2 R ea di n g)
Output Voltage (V)
StepCoilAB CDCoil A High
(EC M J1-28)On On
Coil A Low
(EC M J1-30)On On
Coil B High
(EC M J1-13)On On
Coil B Low
(EC M J1-29)On On

(IAC Valve Close Direction)
(IAC Valve Open Direction)

6E–54 ENGINE DRIVEABILITY AND EMISSIONS
GENERAL DESCRIPTION FOR ELECTRIC
IGNITION SYSTEM
The engine use two ignition coils, one per two cylinders.
A two wire connector provides a battery voltage primary
supply through the ignition fuse.
The ignition control spark timing is the ECM’s method of
controlling the spark advance and the ignition dwell.
The ignition control spark advance and the ignition dwell
are calculated by the ECM using the following inputs.
Engine speed
Crankshaft position (CKP) sensor
Engine coolant temperature (ECT) sensor
Throttle position sensor
Vehicle speed sensor
ECM and ignition system supply voltage
Ignition coil works to generate only the secondary
voltage be receiving the primary voltage from ECM.
The primary voltage is generated at the coil driver
located in the ECM. The coil driver generate the primary
voltage based on the crankshaft position signal. In
accordance with the crankshaft position signal, ignition
coil driver determines the adequate ignition timing and
also cylinder number to ignite.
Ignition timing is determined the coolant temperature,
intake air temperature, engine speed, engine load,
knock sensor signal, etc.
Spark Plug
Although worn or dirty spark plugs may give satisfactory
operation at idling speed, they frequently fail at higher
engine speeds. Faulty spark plugs may cause poor fuel
economy, power loss, loss of speed, hard starting and
generally poor engine performance. Follow the
scheduled maintenance service recommendations to
ensure satisfactory spark plug performance. Refer to
Maintenance and Lubrication.
Normal spark plug operation will result in brown to
grayish-tan deposits appearing on the insulator portion
of the spark plug. A small amount of red-brown, yellow,
and white powdery material may also be present on the
insulator tip around the center electrode. These
deposits are normal combustion by-products of fuels
and lubricating oils with additives. Some electrode wear
will also occur. Engines which are not running properly
are often referred to as “misfiring.” This means the
ignition spark is not igniting the air/fuel mix ture at the
proper time. While other ignition and fuel system causes
must also be considered, possible causes include
ignition system conditions which allow the spark voltage
to reach ground in some other manner than by jumping
across the air gap at the tip of the spark plug, leaving
the air/fuel mix ture unburned. Misfiring may also occur
when the tip of the spark plug becomes overheated and
ignites the mixture before the spark jumps. This is
referred to as “pre-ignition.”
Spark plugs may also misfire due to fouling, ex cessive
gap, or a cracked or broken insulator. If misfiring occursbefore the recommended replacement interval, locate
and correct the cause.
Carbon fouling of the spark plug is indicated by dry,
black carbon (soot) deposits on the portion of the spark
plug in the cylinder. Ex cessive idling and slow speeds
under light engine loads can keep the spark plug
temperatures so low that these deposits are not burned
off. Very rich fuel mix tures or poor ignition system output
may also be the cause. Refer to DTC P1167.
Oil fouling of the spark plug is indicated by wet oily
deposits on the portion of the spark plug in the cylinder,
usually with little electrode wear. This may be caused by
oil during break-in of new or newly overhauled engines.
Deposit fouling of the spark plug occurs when the
normal red-brown, yellow or white deposits of
combustion by-products become sufficient to cause
misfiring. In some cases, these deposits may melt and
form a shiny glaze on the insulator around the center
electrode. If the fouling is found in only one or two
cylinders, valve stem clearances or intake valve seals
may be allowing ex cess lubricating oil to enter the
cylinder, particularly if the deposits are heavier on the
side of the spark plug facing the intake valve.
Ex cessive gap means that the air space between the
center and the side electrodes at the bottom of the
spark plug is too wide for consistent firing. This may be
due to improper gap adjustment or to ex cessive wear of
the electrode during use. A check of the gap size and
comparison to the gap specified for the vehicle in
Maintenance and Lubrication will tell if the gap is too
wide. A spark plug gap that is too small may cause an
unstable idle condition. Ex cessive gap wear can be an
indication of continuous operation at high speeds or
with engine loads, causing the spark to run too hot.
Another possible cause is an ex cessively lean fuel
mixture.

6E–62 ENGINE DRIVEABILITY AND EMISSIONS
Diagnostic Thought Process
As you follow a diagnostic plan, every box on the
Strategy Based Diagnostics chart requires you to use
the diagnostic thought process. This method of thinking
optimizes your diagnosis in the following ways:
Improves your understanding and definition of the
customer complaint
Saves time by avoiding testing and/or replacing good
parts
Allows you to look at the problem from different
perspectives
Guides you to determine what level of understanding
about system operation is needed:
–Owner’s manual level
–Service manual level
–In-depth (engineering) level
–Owner’s manual level
–Service manual level
–In-depth (engineering) level
1. Verify the Complaint
What you should do
To verify the customer complaint, you need to know the
correct (normal) operating behavior of the system and
verify that the customer complaint is a valid failure of the
system.
The following information will help you verify the
complaint:
WHAT the vehicle model/options are
WHAT aftermarket and dealer-installed accessories
exist
WHAT related system(s) operate properly
WHEN the problem occurs
WHERE the problem occurs
HOW the problem occurs
HOW LONG the condition has ex isted (and if the
system ever worked correctly)
HOW OFTEN the problem occurs
Whether the severity of the problem has increased,
decreased or stayed the same
What resources you should use
Whenever possible, you should use the following
resources to assist you in verifying the complaint:
Service manual Theory or Circuit Description
sections
Service manual “System Performance Check”
Owner manual operational description
Technician ex perience
Identical vehicle for comparisonCircuit testing tools
Vehicle road tests
Complaint check sheet
Contact with the customer
2. Perform Preliminary Checks
NOTE: An estimated 10 percent of successful vehicle
repairs are diagnosed with this step!
What you should do
You perform preliminary checks for several reasons:
To detect if the cause of the complaint is VISUALLY
OBVIOUS
To identify parts of the system that work correctly
To accumulate enough data to correctly and
accurately search for a ISUZU Service Bulletin on
ISUZU Web site.
The initial checks may vary depending on the
complex ity of the system and may include the following
actions:
Operate the suspect system
Make a visual inspection of harness routing and
accessible/visible power and ground circuits
Check for blown fuses
Make a visual inspection for separated connectors
Make a visual inspection of connectors (includes
checking terminals for damage and tightness)
Check for any DTCs stored by the on-board
computers
Sense unusual noises, smells, vibrations or
mov ements
Investigate the vehicle service history (call other
dealerships, if appropriate)
What resources you should use
Whenever appropriate, you should use the following
resources for assistance in performing preliminary
checks:
Tech II or other technical equipment for viewing DTCs
Service manual information:
–Component locations
–Harness routing
–Wiring schematics
–Procedures for viewing DTCs
Dealership service history file
Vehicle road test
Identical vehicle or system for comparison

ENGINE DRIVEABILITY AND EMISSIONS 6E–63
3. Check Bulletins and
Troubleshooting Hints
NOTE: As estimated 30 percent of successful vehicle
repairs are diagnosed with this step!
What you should do
You should have enough information gained from
preliminary checks to accurately search for a bulletin
and other related service information. Some service
manual sections provide troubleshooting hints that
match symptoms with specific complaints.
What resources you should use
You should use the following resources for assistance in
checking for bulletins and troubleshooting hints:
Printed bulletins
Access ISUZU Bulletin Web site.
Videotapes
Service manual
4. Perform Service Manual
Diagnostic Checks
What you should do
The “System Checks” in most service manual sections
and in most cells of section 8A (electrical) provide you
with:
A systematic approach to narrowing down the
possible causes of a system fault
Direction to specific diagnostic procedures in the
service manual
Assistance to identify what systems work correctly
What resources you should use
Whenever possible, you should use the following
resources to perform service manual checks:
Service manual
Technical equipment (for viewing DTCs and
analyzing data)
Digital multimeter and circuit testing tools
Other tools as needed
5a and 5b. Perform Service Manual
Diagnostic Procedures
NOTE: An estimated 40 percent of successful vehicle
repairs are diagnosed with these steps!
What you should do
When directed by service manual diagnostic checks,
you must then carefully and accurately perform the
steps of diagnostic procedures to locate the fault relatedto the customer complaint.
What resources you should use
Whenever appropriate, you should use the following
resources to perform service manual diagnostic
procedures:
Service manual
Technical equipment (for analyzing diagnostic data)
Digital multimeter and circuit testing tools
Essential and special tools
5c. Technician Self Diagnoses
When there is no DTC stored and no matching
symptom for the condition identified in the service
manual, you must begin with a thorough understanding
of how the system(s) operates. Efficient use of the
service manual combined with you ex perience and a
good process of elimination will result in accurate
diagnosis of the condition.
What you should do
Step 1: Identify and understand the suspect
circuit(s)
Having completed steps 1 through 4 of the Strategy
Based Diagnostics chart, you should have enough
information to identify the system(s) or sub-system(s)
involved. Using the service manual, you should
determine and investigate the following circuit
characteristics:
Electrical:
–How is the circuit powered (power distribution
charts and/or fuse block details)?
–How is the circuit grounded (ground distribution
charts)?
–How is the circuit controlled or sensed (theory of
operation):
–If it is a switched circuit, is it normally open or
normally closed?
–Is the power switched or is the ground
switched?
–Is it a variable resistance circuit (ECT sensor
or TP sensor, for ex ample)?
–Is it a signal generating device (MAF sensor of
VSS, for example)?
–Does it rely on some mechanical/vacuum
device to operate?
Physical:
–Where are the circuit components (component
locators and wire harness routing diagrams):
–Are there areas where wires could be chafed
or pinched (brackets or frames)?
–Are there areas subjected to ex treme
temperatures?