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Dtc B1551: Serial Communication Circuit Malfunction - Suzuki SX4 Service Manual

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7B-68 Air Conditioning System: Automatic Type

DTC B1551: Serial Communication Circuit Malfunction

Wiring Diagram
[B]: Back-up power supply circuit
[S]: Serial communication circuit
DTC Detecting Condition and Trouble Area
Serial communication signal is higher than or lower than specified value for
specified time continuously.
DTC Troubleshooting
Step
1
Was "Air Conditioning System Check" performed?
2
Back-up power supply circuit fuse check
1) Check back-up power supply circuit fuse for blowing.
Is fuse(s) blown?
3
Wire harness check
1) Turn ignition switch to OFF position.
2) Disconnect connectors from BCM, information display
and HVAC control module.
3) Check for proper connection to serial communication
circuit terminal of BCM, information display and HVAC
control module connectors.
4) If OK, check that serial communication circuit is as
follows.
• Wiring harness resistance of serial communication
circuit is less than 3 Ω
• Insulation resistance between serial communication
circuit terminal and vehicle body ground is Infinity
• Circuit voltage of serial communication circuit is 0 - 1
V with ignition switch turned ON
Are they in good condition?
4
[B]
4
WHT/RED
WHT
14
13
12
11
10
9
30
29
28
27
26
25
DTC detecting condition
Action
1
12V
G20-13
YEL
G20-7
5V
12V
G20
8
7
6
5
24
23
22
21
20
19
1. HVAC control module
2. BCM
Go to Step 2.
Replace blown fuse and
check for short in back-
up power supply circuit.
Go to Step 4.
3
2
[S]
4
3
2
1
18
17
16
15
3. Information display
4. Circuit fuse
Trouble area
• Back-up power supply circuit
• Serial communication circuit
• BCM
• Information display
• HVAC control module
Yes
Go to "Air Conditioning
System Check:
Automatic Type".
Go to Step 3.
Serial communication
circuit is open, short or
high resistance.
S7RW0A7224020
I7RW01722012-02
No

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