Infiniti G37 Coupe. Manual - part 1239

EPS SYSTEM

STC-7

< FUNCTION DIAGNOSIS >

[WITHOUT 4WAS]

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FUNCTION DIAGNOSIS

EPS SYSTEM

System Diagram

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CONTROL DIAGRAM

CROSS-SECTIONAL VIEW

System Description

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• The EPS system controls the power steering solenoid valve through the power steering control unit.

JSGIA0258GB

1.

Unified meter and A/C amp.

2.

Power steering control unit

3.

Power steering solenoid valve

4.

Steering gear assembly

5.

Gear housing assembly

6.

Gear sub-assembly

7.

Pinion

8.

Power steering oil pump

9.

Reservoir tank

SGIA1389E

STC-8

< FUNCTION DIAGNOSIS >

[WITHOUT 4WAS]

EPS SYSTEM

• The valve driving voltage to control the power steering solenoid

valve varies according to the vehicle speed.

OPERATION PRINCIPLE

During Parking (When Turning The Steering Wheel To The Right.)

1.

Power steering solenoid valve is closed while a vehicle is stopped.

2.

Pinion “1R”, “2R” and “3R” are closed depending on steering torque of steering wheel.

3.

Oil pressure “P” in the gear housing assembly is the sum of oil pressures occurred in “2R” and “3R”. This
results in a light steering force because of high pressure.

During High-speed Operation

1.

Power steering solenoid valve is opened during high-speed operation.

2.

Pinion “1R”, “2R” and “3R” are closed depending on steering torque of steering wheel.

3.

Oil pressure “2R” does not occur because the power steering solenoid valve is on full throttle.

4.

Oil pressure “P” in the gear housing assembly includes only oil pressure occurred in “3R” and results in a
heavy steering force.

JSGIA0113GB

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JSGIA0021GB

EPS SYSTEM

STC-9

< FUNCTION DIAGNOSIS >

[WITHOUT 4WAS]

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Component Parts Location

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Component Description

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1.

Power steering solenoid valve

2.

Power steering control unit

A.

Steering gear assembly

B.

Glove box assembly removed

: Vehicle front

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Component parts

Reference/Function

Power steering control unit

• Signals from various sensors control the driving voltage to the power steering solenoid valve.
• The power steering control unit controls the driving voltage to the power steering solenoid valve 

for maintaining the power steering assist force when the fail-safe function is activated. (The en-
gine speed signals control EPS system if any vehicle speed signal error is detected.)

Unified meter and A/C amp.

STC-15, "Description"

ECM

STC-13, "Description"

Power steering solenoid valve

STC-11, "Description"

STC-10

< COMPONENT DIAGNOSIS >

[WITHOUT 4WAS]

POWER SUPPLY AND GROUND CIRCUIT

COMPONENT DIAGNOSIS

POWER SUPPLY AND GROUND CIRCUIT

Description

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• Power supply to EPS system

Diagnosis Procedure

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1.

CHECK POWER SUPPLY

1.

Turn the ignition switch OFF.

2.

Disconnect power steering control unit harness connector.

3.

Check voltage between power steering control unit harness connector and ground.

4.

Turn the ignition switch ON.

CAUTION:

Never start the engine.

5.

Check voltage between power steering control unit harness connector and ground.

Is the inspection result normal?

YES

>> GO TO 2.

NO

>>

Check the following. If any items are damaged, repair or replace damaged parts.

• 10A fuses (#45) open
- Harness for short or open between ignition switch and power steering control unit harness con-

nector No. 3 terminal.

- Ignition switch. Refer to 

SEC-61, "Component Inspection"

.

2.

CHECK GROUND CIRCUIT

1.

Turn the ignition switch OFF.

2.

Check continuity between power steering control unit harness connector and ground.

Also check harness for short to ground and short to power.

Is the inspection result normal?

YES

>> GO TO 3.

NO

>> Repair open circuit or short to power in harness or connectors.

3.

CHECK TERMINALS AND HARNESS CONNECTORS

Check power steering control unit pin terminals for damage or loose connection with harness connector.

Is the inspection result normal?

YES

>> INSPECTION END

NO

>> Repair or replace damaged parts.

Power steering control unit

Voltage (Approx.)

Connector

Terminal

M108

3 – Ground

0 V

Power steering control unit

Voltage (Approx.)

Connector

Terminal

M108

3 – Ground

Battery voltage

Power steering control unit

Continuity

Connector

Terminal

M108

6 – Ground

Existed