INFINITI QX4 2001 Factory Service Manual

Engine Compartment
There are several reasons a vehicle or engine vibration could
cause an electrical complaint. Some of the things to check for are:
IConnectors not fully seated.
IWiring harness not long enough and is being stressed due to
engine vibrations or rocking.
IWires laying across brackets or moving components.
ILoose, dirty or corroded ground wires.
IWires routed too close to hot components.
To inspect components under the hood, start by verifying the integ-
rity of ground connections. (Refer to GROUND INSPECTION
described later.) First check that the system is properly grounded.
Then check for loose connection bygently shakingthe wiring or
components as previously explained. Using the wiring diagrams
inspect the wiring for continuity.
Behind The Instrument Panel
An improperly routed or improperly clamped harness can become
pinched during accessory installation. Vehicle vibration can aggra-
vate a harness which is routed along a bracket or near a screw.
Under Seating Areas
An unclamped or loose harness can cause wiring to be pinched by
seat components (such as slide guides) during vehicle vibration. If
the wiring runs under seating areas, inspect wire routing for pos-
sible damage or pinching.
SGI842
HEAT SENSITIVENBGI0004S0203The owner's problem may occur during hot weather or after car has
sat for a short time. In such cases you will want to check for a heat
sensitive condition.
To determine if an electrical component is heat sensitive, heat the
component with a heat gun or equivalent.
Do not heat components above 60ÉC (140ÉF).If incident occurs
while heating the unit, either replace or properly insulate the com-
ponent.
SGI843
FREEZINGNBGI0004S0204The customer may indicate the incident goes away after the car
warms up (winter time). The cause could be related to water freez-
ing somewhere in the wiring/electrical system.
There are two methods to check for this. The first is to arrange for
the owner to leave his car overnight. Make sure it will get cold
enough to demonstrate his complaint. Leave the car parked out-
side overnight. In the morning, do a quick and thorough diagnosis
of those electrical components which could be affected.
HOW TO PERFORM EFFICIENT DIAGNOSIS FOR AN ELECTRICAL INCIDENT
Incident Simulation Tests (Cont'd)
GI-26

The second method is to put the suspect component into a freezer
long enough for any water to freeze. Reinstall the part into the car
and check for the reoccurrence of the incident. If it occurs, repair
or replace the component.
SGI844
WATER INTRUSIONNBGI0004S0205The incident may occur only during high humidity or in rainy/snowy
weather. In such cases the incident could be caused by water
intrusion on an electrical part. This can be simulated by soaking the
car or running it through a car wash.
Do not spray water directly on any electrical components.
SGI845
ELECTRICAL LOADNBGI0004S0206The incident may be electrical load sensitive. Perform diagnosis
with all accessories (including A/C, rear window defogger, radio,
fog lamps) turned on.
COLD OR HOT START UPNBGI0004S0207On some occasions an electrical incident may occur only when the
car is started cold. Or it may occur when the car is restarted hot
shortly after being turned off. In these cases you may have to keep
the car overnight to make a proper diagnosis.
Circuit InspectionNBGI0004S03INTRODUCTIONNBGI0004S0302In general, testing electrical circuits is an easy task if it is
approached in a logical and organized method. Before beginning
it is important to have all available information on the system to be
tested. Also, get a thorough understanding of system operation.
Then you will be able to use the appropriate equipment and follow
the correct test procedure.
You may have to simulate vehicle vibrations while testing electrical
components.Gently shakethe wiring harness or electrical com-
ponent to do this.
OPEN A circuit is open when there is no continuity through a section of
the circuit.
SHORT There are two types of shorts.
ISHORT CIRCUIT When a circuit contacts another circuit
and causes the normal resistance to
change.
ISHORT TO GROUND When a circuit contacts a ground
source and grounds the circuit.
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HOW TO PERFORM EFFICIENT DIAGNOSIS FOR AN ELECTRICAL INCIDENT
Incident Simulation Tests (Cont'd)
GI-27

NOTE:
Refer to ªHOW TO CHECK TERMINALº in GI-21 to probe or
check terminal.
TESTING FOR ªOPENSº IN THE CIRCUITNBGI0004S0303Before you begin to diagnose and test the system, you should
rough sketch a schematic of the system. This will help you to logi-
cally walk through the diagnosis process. Drawing the sketch will
also reinforce your working knowledge of the system.
SGI846
Continuity Check Method
The continuity check is used to find an open in the circuit. The
Digital Multimeter (DMM) set on the resistance function will indicate
an open circuit as over limit (no beep tone or no ohms symbol).
Make sure to always start with the DMM at the highest resistance
level.
To help in understanding the diagnosis of open circuits please refer
to the schematic above.
1) Disconnect the battery negative cable.
2) Start at one end of the circuit and work your way to the other
end. (At the fuse block in this example)
3) Connect one probe of the DMM to the fuse block terminal on
the load side.
4) Connect the other probe to the fuse block (power) side of SW1.
Little or no resistance will indicate that portion of the circuit has
good continuity. If there were an open in the circuit, the DMM
would indicate an over limit or infinite resistance condition.
(point A)
5) Connect the probes between SW1 and the relay. Little or no
resistance will indicate that portion of the circuit has good con-
tinuity. If there were an open in the circuit, the DMM would
indicate an over limit or infinite resistance condition. (point B)
6) Connect the probes between the relay and the solenoid. Little
or no resistance will indicate that portion of the circuit has good
continuity. If there were an open in the circuit, the DMM would
indicate an over limit or infinite resistance condition. (point C)
Any circuit can be diagnosed using the approach in the above
example.
Voltage Check Method
To help in understanding the diagnosis of open circuits please refer
to the previous schematic.
In any powered circuit, an open can be found by methodically
checking the system for the presence of voltage. This is done by
switching the DMM to the voltage function.
1) Connect one probe of the DMM to a known good ground.
2) Begin probing at one end of the circuit and work your way to
the other end.
3) With SW1 open, probe at SW1 to check for voltage.
HOW TO PERFORM EFFICIENT DIAGNOSIS FOR AN ELECTRICAL INCIDENT
Circuit Inspection (Cont'd)
GI-28

voltage; open is further down the circuit than SW1.
no voltage; open is between fuse block and SW1 (point A).
4) Close SW1 and probe at relay.
voltage; open is further down the circuit than the relay.
no voltage; open is between SW1 and relay (point B).
5) Close the relay and probe at the solenoid.
voltage; open is further down the circuit than the solenoid.
no voltage; open is between relay and solenoid (point C).
Any powered circuit can be diagnosed using the approach in the
above example.
TESTING FOR ªSHORTSº IN THE CIRCUITNBGI0004S0304To simplify the discussion of shorts in the system please refer to
the schematic below.
SGI847
Resistance Check Method
1) Disconnect the battery negative cable and remove the blown
fuse.
2) Disconnect all loads (SW1 open, relay disconnected and sole-
noid disconnected) powered through the fuse.
3) Connect one probe of the ohmmeter to the load side of the fuse
terminal. Connect the other probe to a known good ground.
4) With SW1 open, check for continuity.
continuity; short is between fuse terminal and SW1 (point A).
no continuity; short is further down the circuit than SW1.
5) Close SW1 and disconnect the relay. Put probes at the load
side of fuse terminal and a known good ground. Then, check
for continuity.
continuity; short is between SW1 and the relay (point B).
no continuity; short is further down the circuit than the relay.
6) Close SW1 and jump the relay contacts with jumper wire. Put
probes at the load side of fuse terminal and a known good
ground. Then, check for continuity.
continuity; short is between relay and solenoid (point C).
no continuity; check solenoid, retrace steps.
Voltage Check Method
1) Remove the blown fuse and disconnect all loads (i.e. SW1
open, relay disconnected and solenoid disconnected) powered
through the fuse.
2) Turn the ignition key to the ON or START position. Verify bat-
tery voltage at the B + side of the fuse terminal (one lead on
the B + terminal side of the fuse block and one lead on a known
good ground).
3) With SW1 open and the DMM leads across both fuse
terminals, check for voltage.
voltage; short is between fuse block and SW1 (point A).
no voltage; short is further down the circuit than SW1.
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HOW TO PERFORM EFFICIENT DIAGNOSIS FOR AN ELECTRICAL INCIDENT
Circuit Inspection (Cont'd)
GI-29

4) With SW1 closed, relay and solenoid disconnected and the
DMM leads across both fuse terminals, check for voltage.
voltage; short is between SW1 and the relay (point B).
no voltage; short is further down the circuit than the relay.
5) With SW1 closed, relay contacts jumped with fused jumper
wire check for voltage.
voltage; short is down the circuit of the relay or between the
relay and the disconnected solenoid (point C).
no voltage; retrace steps and check power to fuse block.
GROUND INSPECTIONNBGI0004S0305Ground connections are very important to the proper operation of
electrical and electronic circuits. Ground connections are often
exposed to moisture, dirt and other corrosive elements. The corro-
sion (rust) can become an unwanted resistance. This unwanted
resistance can change the way a circuit works.
Electronically controlled circuits are very sensitive to proper
grounding. A loose or corroded ground can drastically affect an
electronically controlled circuit. A poor or corroded ground can eas-
ily affect the circuit. Even when the ground connection looks clean,
there can be a thin film of rust on the surface.
When inspecting a ground connection follow these rules:
1) Remove the ground bolt or screw.
2) Inspect all mating surfaces for tarnish, dirt, rust, etc.
3) Clean as required to assure good contact.
4) Reinstall bolt or screw securely.
5) Inspect for ªadd-onº accessories which may be interfering with
the ground circuit.
6) If several wires are crimped into one ground eyelet terminal,
check for proper crimps. Make sure all of the wires are clean,
securely fastened and providing a good ground path. If multiple
wires are cased in one eyelet make sure no ground wires have
excess wire insulation.
SGI853
VOLTAGE DROP TESTSNBGI0004S0306Voltage drop tests are often used to find components or circuits
which have excessive resistance. A voltage drop in a circuit is
caused by a resistancewhen the circuit is in operation.
Check the wire in the illustration. When measuring resistance with
HOW TO PERFORM EFFICIENT DIAGNOSIS FOR AN ELECTRICAL INCIDENT
Circuit Inspection (Cont'd)
GI-30

ohmmeter, contact by a single strand of wire will give reading of 0
ohms. This would indicate a good circuit. When the circuit operates,
this single strand of wire is not able to carry the current. The single
strand will have a high resistance to the current. This will be picked
up as a slight voltage drop.
Unwanted resistance can be caused by many situations as follows:
IUndersized wiring (single strand example)
ICorrosion on switch contacts
ILoose wire connections or splices.
If repairs are needed always use wire that is of the same or larger
gauge.
Measuring Voltage Drop Ð Accumulated Method
1) Connect the voltmeter across the connector or part of the cir-
cuit you want to check. The positive lead of the voltmeter
should be closer to power and the negative lead closer to
ground.
2) Operate the circuit.
3) The voltmeter will indicate how many volts are being used to
ªpushº current through that part of the circuit.
Note in the illustration that there is an excessive 4.1 volt drop
between the battery and the bulb.
SGI974
Measuring Voltage Drop Ð Step by Step
The step by step method is most useful for isolating excessive
drops in low voltage systems (such as those in ªComputer Con-
trolled Systemsº).
Circuits in the ªComputer Controlled Systemº operate on very low
amperage.
The (Computer Controlled) system operations can be adversely
affected by any variation in resistance in the system. Such resis-
tance variation may be caused by poor connection, improper
installation, improper wire gauge or corrosion.
The step by step voltage drop test can identify a component or wire
with too much resistance.
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HOW TO PERFORM EFFICIENT DIAGNOSIS FOR AN ELECTRICAL INCIDENT
Circuit Inspection (Cont'd)
GI-31

SGI854
CONTROL UNIT CIRCUIT TESTNBGI0004S0307System Description: When the switch is ON, the control unit lights
up the lamp.
MGI034A
Input-output voltage chart
Pin No. Item ConditionVoltage
value [V]In case of high resistance such as single strand [V]
*
1 Switch Switch ON Battery voltage Lower than battery voltage Approx. 8 (Example)
Switch OFF Approx. 0 Approx. 0
2 Lamp Switch ON Battery voltage Approx. 0 (Inoperative lamp)
Switch OFF Approx. 0 Approx. 0
The voltage value is based on the body ground.
* : If high resistance exists in the switch side circuit (caused by a single strand), terminal 1 does not detect battery voltage. Control unit
does not detect the switch is ON even if the switch does not turn ON. Therefore, the control unit does not supply power to light up the
lamp.
HOW TO PERFORM EFFICIENT DIAGNOSIS FOR AN ELECTRICAL INCIDENT
Circuit Inspection (Cont'd)
GI-32

MGI035A
Input-output voltage chart
Pin No. Item ConditionVoltage
value [V]In case of high resistance such as single strand [V]
*
1 Lamp Switch ON Approx. 0 Battery voltage (Inoperative lamp)
Switch OFF Battery voltage Battery voltage
2 Switch Switch ON Approx. 0 Higher than 0 Approx. 4 (Example)
Switch OFF Approx. 5 Approx. 5
The voltage value is based on the body ground.
* : If high resistance exists in the switch side circuit (caused by a single strand), terminal 2 does not detect approx. 0V. Control unit
does not detect the switch is ON even if the switch does not turn ON. Therefore, the control unit does not control ground to light up the
lamp.
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HOW TO PERFORM EFFICIENT DIAGNOSIS FOR AN ELECTRICAL INCIDENT
Circuit Inspection (Cont'd)
GI-33

NBGI0005
NOTICE:
Trouble diagnoses indicates work procedures required to diagnose
problems effectively. Observe the following instructions before
diagnosing.
1)Before performing trouble diagnoses, read the ªPrelimi-
nary Checkº, the ªSymptom Chartº or the ªWork Flowº.
2)After repairs, re-check that the problem has been com-
pletely eliminated.
3)Refer to Component Parts and Harness Connector Loca-
tion for the Systems described in each section for
identification/location of components and harness con-
nectors.
4)Refer to the Circuit Diagram for quick pinpoint check.
If you need to check circuit continuity between harness
connectors in more detail, such as when a sub-harness is
used, refer to Wiring Diagram in each individual section
and Harness Layout in EL section for identification of har-
ness connectors.
5)When checking circuit continuity, ignition switch should
be OFF.
6)Before checking voltage at connectors, check battery volt-
age.
7)After accomplishing the Diagnostic Procedures and Elec-
trical Components Inspection, make sure that all harness
connectors are reconnected as they were.
HOW TO FOLLOW TROUBLE DIAGNOSIS
GI-34

How to Follow Test Groups in Trouble
Diagnosis
NBGI0005S01
SGI138A
1)Work and diagnostic procedure
Start to diagnose a problem using procedures indicated in
enclosed test groups.
2)Questions and required results.
Questions and required results are indicated in bold type in test
group.
The meaning of are as follows:
a. Battery voltage®11 - 14V or approximately 12V
b. Voltage: Approximately 0V®Less than 1V
3)Symbol used in illustration
Symbols included in illustrations refer to measurements or pro-
cedures. Before diagnosing a problem, familiarize yourself with
each symbol. Refer to ªCONNECTOR SYMBOLSº (GI-15) and
ªKey to Symbols Signifying Measurements or Proceduresº (GI-
36).
4)Action items
Next action for each test group is indicated based on result of
each question. Test group number is shown in the left upper
portion of each test group.
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HOW TO FOLLOW TROUBLE DIAGNOSIS
How to Follow Test Groups in Trouble Diagnosis
GI-35