LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Suzuki >> 2012 >> SX4 Base >> Repair and Diagnosis >> Heating, Ventilation & A/C (HVAC) >> HVAC Control Systems >> Air Conditioning System - Auto A/C >> Diagnostic Information and Procedures >> DTC B1551: Serial Communication Circuit Malfunction >> DTC Troubleshooting
April 5, 2026: LEMON Manuals is launched! Read the announcement.

DTC Troubleshooting

B1551: SYMPTOM TROUBLESHOOTING REFERENCE CHART

Step Action YES NO
1  Was "Air Conditioning System Check" performed?  Go to Step 2. Go to AIR CONDITIONING SYSTEM CHECK: AUTO A/C .
2  Backup power supply circuit fuse check 
  1. Check backup power supply circuit fuse for blowing.

Is fuse(s) blown? 		 Replace blown fuse and check for short in backup power supply circuit. Go to Step 3.
3  Wire harness check 
  1. Turn ignition switch to OFF position.
  2. Disconnect connectors from BCM and HVAC control module.
  3. Check for proper connection to serial communication circuit terminal of BCM 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? 		 Go to Step 4. Serial communication circuit is open, short or high resistance.
4  Communication data check 
  1. Connect connectors to BCM and HVAC control module with ignition switch turned OFF.
  2. Check that serial communication signal is output from BCM referring to "Voltage Check" under INSPECTION OF BCM AND ITS CIRCUITS .

Is serial communication signal output? 		 Substitute a known-good HVAC control module and recheck. Substitute a known-good BCM and recheck.
scientia non olet · About LEMON Manuals