MACS Monthly Newsletter - 2021 - DEC6

1. NOTE: The Highlighting feature is NOT a Power Flow
feature.
Low Speed Fan Control Operation
The schematic in Figure 9 exemplifies just how important
splices can be to the operational characteristics of
a circuit. The current flow will be altered by the cooling
fan relays to control the cooling fans to best suit the thermal
management needs of the engine and interconnected
parts that need to be kept cool by the coolant. Each
splice has a unique connection that permits the fans to
run in series to achieve low speed, connected in parallel
to achieve high speed or operate the fans independently.
A technician working on any complex controlled systems,
like these cooling fans, must understand the operational
control functions in order to determine where any circuit
deficiencies may be.
Figure 10: This logic table is designed to help understand
the low speed fan control
High Speed Fan Control Operation
Figure 11 shows supply voltage and ground for Cooling
Fan Relay 1 coil is supplied by the Intelligent Power Distribution
Module (IPDM). With continuous B+ power available
from the 40A Fuse P, Pin 84 of the IPDM now has
power to the switch side of Cooling Fan Relay 1. With the
relay energized, power can flow through the relay to pin
85 of the IPDM, which now provides power to Cooling Fan
Relay 2 (Pins 2 and 5) and Cooling Fan Motor 2 terminals 1
and 2. Although these two circuits are wired in parallel to
each other, they are not running in parallel.
Figure 9: Splices are very important to the operational
characteristics of a circuit.
NOTE: The power flow through the circuit above is illustrated
to show Low Speed Fan operation.
TECH TIP: Due to the way the circuit is wired,
all the current to operate the cooling fans is going
through the control relays. A technician must understand
that certain component malfunctions, such
as blown fuses, and inoperative relays, are going to
warrant further circuit analysis of amperage draw
of the cooling fan motors. A relay replacement will
certainly prematurely fail if the motor is drawing too
much current.
Add Some Logic
Let us put some logic on the table. If you have taken
any ASE electrical/electronic or transmission exams in the
past, then you should be familiar with logic tables. By using
logic tables (Figure 10), it helps us understand relay
control and the actions taken to control a load, such as a
motor or solenoid.
December 2021
6
Figure 11: Supply voltage and ground for Cooling Fan Relay
1 coil is supplied by the IPDM.
With Cooling Fan Relay 2 de-energized (OFF), all the
voltage potential is routed via the PINK wire to Cooling
Fan Motor 2 terminals 1 and 2 through the motor, which
has ground supplied at F2. Cooling Fan Motor 2 is now
running on high speed due to full battery voltage available
to the motor.
The IPDM energizes Cooling Fan Relay 3 by grounding
Pin 106. With Cooling Fan Relay 3 energized, Cooling Fan
Motor 1 can also run at full speed. Power for Cooling Fan
Motor 1 is provided by the 40 A Fuse O to terminals 1 and
2. With Cooling Fan Relay 3 energized, the switch side of
the relay closes, which completes the circuit from terminal
3 to 5 of the relay. Terminal 5 of Cooling Fan Relay 3 is connected
to ground at F1, which completes the circuit and
enables Cooling Fan Motor 1 to operate on high speed.
See the logic table in Figure 12.
MACS Service Reports
nissan-techinfo.com
Peter Orlando
nissan-techinfo.com
http://www.nissan-techinfo.com http://www.nissan-techinfo.com
MACS Monthly Newsletter - 2021

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