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DTC P1623: Unregistered Transponder: Troubleshooting

WARNING: This page is about a different car, the 2007 Suzuki Grand Vitara and 2006 Suzuki Grand Vitara. However, it is still accessible from the selected car via links, so may be relevant.
TROUBLESHOOTING CHART

Step Action YES NO
Diagnostic Trouble Code (DTC) confirmation 
  1. Clear DTC(s) referring to DIAGNOSTIC TROUBLE CODE (DTC) CLEARANCE .
  2. Turn the ignition switch to OFF position.
  3. Check if any DTC is detected referring to DIAGNOSTIC TROUBLE CODE (DTC) CHECK .

Is DTC P1623 still detected? 
Go to Step 2. The troubleshooting is completed.
Diagnostic Trouble Code (DTC) check 
Is any DTC other than P1623 is detected in Step 1? 
Perform the troubleshooting referring to the corresponding flowchart, and then go to Step 3. Go to Step 3.
Registration of the unregistered ignition key with ECM and Diagnostic Trouble Code (DTC) check 
  1. Register the transponder code in the transponder in the unregistered ignition key with ECM referring to REGISTRATION OF THE IGNITION KEY .
  2. Check if that DTC P1623 is detected referring to DIAGNOSTIC TROUBLE CODE (DTC) CHECK .

Is DTC P1623 detected? 
Go to Step 4. The troubleshooting is completed.
ICM check 
  1. Check ICM referring to INSPECTION OF IMMOBILIZER CONTROL MODULE (ICM) AND ITS CIRCUIT .

Is immobilizer controller assembly normal? 
Replace ECM with new one referring to ENGINE CONTROL MODULE (ECM) REMOVAL AND INSTALLATION , and then perform PROCEDURE AFTER ECM REPLACEMENT . Replace ICM with new one referring to IMMOBILIZER CONTROL MODULE (ICM) REMOVAL AND INSTALLATION .