Infiniti M35/M45 Y50. Manual — part 795
SERVICE INFORMATION FOR ELECTRICAL INCIDENT
GI-33
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no voltage; short is further down the circuit than SW1.
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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.
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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 Inspection
Ground 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 corrosion (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 drasti-
cally affect an electronically controlled circuit. A poor or corroded ground can easily 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:
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Remove the ground bolt or screw.
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Inspect all mating surfaces for tarnish, dirt, rust, etc.
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Clean as required to assure good contact.
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Reinstall bolt or screw securely.
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Inspect for “add-on” accessories which may be interfering with the ground circuit.
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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.
For detailed ground distribution information, refer to “Ground Distribution” in PG section.
Voltage Drop Tests
Voltage drop tests are often used to find components or circuits which have excessive resistance. A voltage
drop in a circuit is caused by a resistance when the circuit is in operation.
Check the wire in the illustration. When measuring resistance with DMM, 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:
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Undersized wiring (single strand example)
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Corrosion on switch contacts
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Loose wire connections or splices.
SGI853
GI-34
SERVICE INFORMATION FOR ELECTRICAL INCIDENT
If repairs are needed always use wire that is of the same or larger gauge.
MEASURING VOLTAGE DROP — ACCUMULATED METHOD
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Connect the DMM across the connector or part of the circuit you want to check. The positive lead of the
DMM should be closer to power and the negative lead closer to ground.
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Operate the circuit.
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The DMM will indicate how many volts are being used to “push” 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.
MEASURING VOLTAGE DROP — STEP-BY-STEP
The step-by-step method is most useful for isolating excessive drops in low voltage systems (such as those in
“Computer Controlled Systems”).
Circuits in the “Computer Controlled System” operate on very low amperage.
The (Computer Controlled) system operations can be adversely affected by any variation in resistance in the
system. Such resistance 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.
SGI974
SAIA0258E
SERVICE INFORMATION FOR ELECTRICAL INCIDENT
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Control Unit Circuit Test
System Description:When the switch is ON, the control unit lights up the lamp.
INPUT-OUTPUT VOLTAGE CHART
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.
INPUT-OUTPUT VOLTAGE CHART
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.
MGI034A
Pin
No.
Item
Condition
Voltage
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
MGI035A
Pin
No.
Item
Condition
Voltage
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
GI-36
SERVICE INFORMATION FOR ELECTRICAL INCIDENT
Control Units and Electrical Parts
NAS0008Y
PRECAUTIONS
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Never reverse polarity of battery terminals.
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Install only parts specified for a vehicle.
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Before replacing the control unit, check the input and output and functions of the component parts.
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Do not apply excessive force when disconnecting a connector.
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Do not apply excessive shock to the control unit by dropping or
hitting it.
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Be careful to prevent condensation in the control unit due to
rapid temperature changes and do not let water or rain get on it.
If water is found in the control unit, dry it fully and then install it in
the vehicle.
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Be careful not to let oil to get on the control unit connector.
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Avoid cleaning the control unit with volatile oil.
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Do not disassemble the control unit, and do not remove the
upper and lower covers.
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When using a DMM, be careful not to let test probes get close to
each other to prevent the power transistor in the control unit
from damaging battery voltage because of short circuiting.
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When checking input and output signals of the control unit, use
the specified check adapter.
SAIA0255E
SEF348N
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