Kia Forte: Fuses And Relays / Integrated Central Control Unit (ICU)

Kia Forte 2019-2024 (BD) Service Manual / Body Electrical System / Fuses And Relays / Integrated Central Control Unit (ICU)

Components and components location
Component Location

1. Integrated central control unit (ICU)

Description and operation

Communication Network Diagram

Airbag Control Unit
Motor Driven Power Steering
Lane Keeping Assist
Blind-Spot Collision Warning
Integrated Body Control Unit
Integrated Central Control Unit
Manual Temp Control
Dual Automatic Temp Control
Occupant Detection System
Powertrain control module
Anti-Lock Braking System

Integrated Central Control Unit (ICU)

ICU (Integrated Central Control Unit) is an integrated model of smart junction block and central gateway.

It performs the function of conventional "Smart junction block" and the function of communication medium of "Central Gateway".

Central Gateway (CGW)

CGW is a controller enabling communication among the controllers connected to the different networks.

There are five CAN networks connected to CGW. B-CAN and M-CAN are connected to the low-speed CAN, C-CAN and P-CAN to the high-speed CAN while D-CAN is connected for inspection.


CGW Main Features


Routing : Information exchange among different in-vehicle communication networks.


Network security control : It only allows inspection communication (D-CAN) to connect in-vehicle communication network in order to prevent


Additional functions

If alarm light is ON, carry out remote diagnosis of Chassis system (C-CAN) through I-Box and gateway


I-Box remote diagnosis (C-CAN) function via gateway shall be suspended.

Dark current measurement: After sending forced electronic parts sleep message to each network from the diagnosis equipment, gateway also enters sleep mode.

Operation current check: Check problem through operation of electronic parts


Fault diagnosis on CAN signal transmission failure by communication control defect

(CGW records DTC for the controller with transmission failure.)


How to check CGW


Although "No CGW CAN signal (TIMEOUT)" record appears when checking the DTC of the faulty electronic component, never determine it as the CGW failure. CGW is a controller that intermediates in-vehicle transmitting/receiving controllers. If one of the following two cases arises : (1) the transmitting controller fails to send a message to CGW, leading to CGW failing to send it to the receiving controller; (2) CGW sends the pre-determined value (Timeout Value), the corresponding receiver records the DTC of the failure of message transmission. Thus, to finally determine the controller that fails to send CAN signal, the DTC of CGW shall be checked. CGW records DTC only when it fails to receive the signal for more than 10 seconds with KEY ON. To identify the cause of no CAN signal transmission, the CGW DTC shall be checked after waiting for more than 20 seconds with KEY ON.


If the CAN communication control unit is not reinstalled after being removed from the vehicle, CGW records the DTC of 'No CAN signal' for the unit.


For example, the failure code of 'DDM CAN signal is not out' is created when the removed DDM is not reinstalled.

If a DTC remains after replacing electronic components and the failure code is not erased, check whether the connector of the electronic component is properly connected, and whether the controller's CAN wiring operates normally. In case that the removed electronic component cannot be reinstalled, ‘Erase Expected Network Config' service shall be performed. Refer to the DTC inspection guide for each failure code for the service execution method.

Otherwise, the DTC of "No CAN Signal" on the corresponding controller may not be deleted.


Perform the "Additional function" > "Network setting initialization" in examining device (KDS) by referring to DTC guide.


IGN2 of SJB is ON when MCU is out of order (State of non-operation due to the external physical or electrical shock). The safety of the driver is secured by forcible lighting on the head lamp low, external and internal tail lamps when the headlamp low switch is ON.


IGN2 is ON when the data transmitting/receiving is impossible by the failure on the CAN communication line (Both of high/low cables are shorted, BAT short in high/low, GND short in high/low) in case of failure on CAN communication line connected to SJB module. When the headlamp low switch is ON, the headlamp low and internal/external tail lamps are lighted forcibly.

Smart Junction Block(SJB)

Smart Junction Block (SJB) is a module that performs the function of conventional Junction Box and some functions of IBU.

It controls various components including lamps by using CAN communication and IPS (replacing the function of fuse and relay) or ARISU.

IPS stands for Intelligent Power Switch, which uses the semiconductor technology to replace the current role of fuse and relay.

The IPS chip has two functions :

1) the high current-based component control;

2) component protection from overcurrent.


The advantages of IPS are as follows:

Reduce relay and consequently decrease weight and volume

Remove the relay operation noise

No need to replace fuses and increase the product life

Capable to diagnose faulty parts

SJB control entry


Switch signal input


Assist seat belt switch

Assist seat belt reminder switch

Assist the door switch

Driver's seat belt switch

Driver's seat belt switch

Rear left seats door switch

Rear right seats door switch

Rear Safety seat belt switch Left

Rear Safety seat belt switch Right

Rear Center seat safety belt switch

IGN1 switch

IGN2 switch

Brake fluid sensor

Trunk open switch

Trunk lid handle switch

HID head lamp option

ADV HID head lamp option

Emergency switch

Headlight low beams switch

Hood switch

Dark disconnect switch

Left front / rear turn signal switch

Right front / rear turn signal switch



Left Headlight low beams

Right Headlight low beams

Right Headlight high beams

Right Headlight high beams

Front left / right fog lamp

Room Taillight

Outdoor Left taillight

Outdoor Light taillight

Left front / rear turn signals

Right front / rear turn signals

Static bending left lamps

Static bending right lamp

DRL Left lamp

DRL right lamp

Trunk room lamp

Body resistance Cut control

Front left turn signal output

Front right turn signal output


Relay Control

Rear glass heat rays relay

Anti-theft alarm horn relay

Trunk lid relay

Room lamp relay

Front glass heat rays relay

Rear fog lamp relay

Headlight high beams relay


SJB protection


PCL (Programmable Current Limit) functions

PCL replaces the junction box function of protecting wires.

How to operate : If the lamp current exceeds the standard level, cut off the current to protect the lamp.

Lamp cut off time : 300ms or less.

Applied components : all lamp components controlled by SJB

Output the error code according to the error detection conditions.


OCL (Open Current Limit)

OCL detects the lamp open state and informs the user of it.

How to operate : Detect the current of the lamp and if it is below the standard level, change the lamp operation.

Applied components : 4 turn signal lamps

Output the error code according to the error detection conditions.


SJB fail safe function


When the MCU is out of order (not operating due to a physical or electrical shock from the outside), and IGN2 and head lamp low switch are on, SJB forces the head lamp low and exterior/interior lamps to turn on in order to secure the driver’s safety.


When the data transmission/reception fails due to a failed CAN communication line connected with SJB module (disconnection of both high and low line, high/low BAT short, high/low GND short), the head lamp low and interior/exterior tail lamps are forced to turn on if IGN2 is on and the head lamp low switch is on.


Auto Cut System of Dark Current


Description : It cuts automatically power to be provided with components for reducing useless dark current according to vehicle state.


SJB had 3 modes, "Normal Mode", "Sleep Mode", "Power Off Mode". Auto cut of dark current practice in "Sleep Mode".

"Sleep" condition : IG OFF, constant input switch, CAN network doesn't activate.

"Sleep" resolutive condition : Any switch inputs, CAN network activates, KEY ON, IGN ON

"Power OFF" condition : The setting time of timer which is used by cutting a load power expires.

"Normal Mode" : SJB function normally activates.

"Sleep Mode" : It is low power mode and activates for reducing electricity consumption of SJB or IPM. Auto cut of dark current function activates.

"Power OFF Mode" : Power of MCU and circumferential circuit is cut for minimizing electricity consumption. Operation stops.


The explanation - The auto cut of dark current

Before delivering to customer
Fuse switch OFF

All door close & RKE door lock or Constant switch state

(Auto cut of dark current scenario starts.)

After "sleep" state is for 20 min.

SJB power down(SJB dark current : 200 μA) and cutting power of Lamp

/Body Load/Wake up

After delivering to customer
Fuse switch ON

All door close & Constant switch state : C_BAState=OFF

(Auto cut of dark current scenario starts.)

After "sleep" state is for 20 min.

SJB power down(SJB dark current : 200 μA) and cutting power of Lamp Load

In case RKE door lock : C_BAState=ON & Trunk SW=CLOSE

(Auto cut of dark current scenario starts.)

After "Sleep" state 35s-65s (Waiting time of other unit : 30-60s + SJB

sleep counts 5s)

SJB Powerdown(SJB dark current : 200 μA) and cutting power of

Lamp Load 


Problem when fuse switch setting is wrong

: If a fuse switch is set to OFF(Before delivering to customer) by a customer or technician and auto cut function of dark current activates, the following problems may occur.

Related part

Door lock/unlock, trunk open don't activate by RKE.

(Wakeup of each module don't activate.)


Digital clock is reset.(Memory is reset.)

Digital clock

Audio setting values (volume, frequency setting) are reset.

(Memory is reset.)


* If fuse switch OFF(before delivering to customer) is set, power of IBU, Digital clock and audio is shut off.

Repair procedures
Fuse Inspection

Check that the fuse holders are loosely held and that the fuses are securely fixed by the holders.


Check that each fuse circuit has the exact fuse capacity.


Check the fuses for any damage.


If a fuse is to be replaced, be sure to use a new fuse of the same capacity. Always identify the cause of the blown fuse and completely eliminate the problem before installing a new fuse.

Diagnosis with KDS

In the body electrical system, failure can be quickly diagnosed by using the vehicle diagnostic system (KDS).

The diagnostic system (KDS) provides the following information.


Self diagnosis : Checking failure and code number (DTC).


Current data : Checking the system input/output data state.


Actuation test : Checking the system operation condition.


Additional function : Controlling other features including system option setting and zero point adjustment.


Select the 'Car model' and the 'Integrated Central Control Unit (ICU)' to be checked in order to check the vehicle with the tester.


Select the 'Current Data' menu to search the current state of the input/output data.


To forcibly actuate the input value of the module to be checked, select option 'Actuation Test'


If you want to change user option, select "user option".


Disconnect the negative (-) battery terminal.


Remove the crash pad lower panel.

(Refer to Body - "Crash Pad Lower Panel")


Remove the crash pad side switch assembly (A) after loosening the mounting screws.


Disconnect the crash pad side switch assembly connector (A).


Remove the ICU (A) by loosening the nuts after disconnecting the connector.


Disconnect the connector (A) from the ICU.


Install in the reverse order of removal.

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