LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Suzuki >> 2006 >> Grand Vitara Base, AWD, Standard >> Repair and Diagnosis (Single Page) >> Accessories & Equipment >> Anti-Theft Systems >> Immobilizer System >> Diagnostic Information And Procedures >> DTC P1621: Immobilizer Communication Line Error >> Troubleshooting
April 5, 2026: LEMON Manuals is launched! Read the announcement.

DTC P1621: Immobilizer Communication Line Error: Troubleshooting

TROUBLESHOOTING CHART

Step Action YES NO
1  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 P1621 still detected? 		 Go to Step 2. The troubleshooting is completed.
2  Fuse check 
  1. Check if any related fuse is blown.

Is any fuse blown? 		 Replace blown fuse(s) with new one(s). Go to Step 3.
3  ICM poor connection check 
  1. Disconnect ICM connector "G24" referring to IMMOBILIZER CONTROL MODULE (ICM) REMOVAL AND INSTALLATION .
  2. Check if wire connections are normal at ICM connector "G24".

Is each wire connection normal? 		 Go to Step 4. Repair poor connection(s).
4  ECM poor connection check 
  1. Disconnect ECM connector "E23" referring to ENGINE CONTROL MODULE (ECM) REMOVAL AND INSTALLATION .
  2. Check if wire connections at "E23-11" and "E23-19" wire terminals are normal.

Is each wire connection normal? 		 Go to Step 5. Repair poor connection(s).
5  Check for open in power supply wire circuit 
  1. Connect ICM connector "G24" referring to IMMOBILIZER CONTROL MODULE (ICM) REMOVAL AND INSTALLATION .
  2. With the ignition switch at ON position, check voltage between "G24-1" wire terminal at ICM and body ground.

Is voltage about 12 V? 		 Go to Step 6. Repair open in power supply wire circuit.
6  Check for open in ground wire circuit 
  1. With the ignition switch at ON position, check voltage between "G24-2" wire terminal at ICM and body ground.

Is voltage 0? 		 Go to Step 7. Repair open in ground wire circuit.
7  Check for open in communication wire circuit 
  1. Disconnect ICM connector "G24" referring to IMMOBILIZER CONTROL MODULE (ICM) REMOVAL AND INSTALLATION .
  2. Disconnect ECM connector "E23" referring to ENGINE CONTROL MODULE (ECM) REMOVAL AND INSTALLATION .
  3. Check resistance between "G24-3" wire terminal at ICM connector and "E23-19" wire terminal at ECM connector.

Is resistance infinite? 		 Repair open in communication wire circuit. Go to Step 8.
8  Check for short to ground circuit in communication wire circuit 
  1. With ICM connector "G24" and ECM connector "E23" disconnected, check resistance between "G24-3" wire terminal at ICM connector and body ground.

Is resistance infinite? 		 Go to Step 9. Repair short to ground wire circuit in communication wire circuit.
9  Check for short to power circuit in communication wire circuit 
  1. With ICM connector "G24" and ECM connector "E23" disconnected, turn the ignition switch to ON position.
  2. Check voltage between "G24-3" wire terminal at ICM connector and body ground.

Is voltage 0 V? 		 Go to Step 10. Repair short to power supply wire circuit in communication wire circuit.
10  Check for open in communication wire circuit 
  1. With ICM connector "G24" and ECM connector "E23" disconnected, check resistance between "G24-4" wire terminal at ICM connector and "E23-11" wire terminal at ECM connector.

Is resistance infinite? 		 Repair open in communication wire circuit. Go to Step 11.
11  Check for short to ground wire circuit in communication wire circuit 
  1. With ICM connector "G24" and ECM connector "E23" disconnected, check resistance between "G24-4" wire terminal at ICM connector and body ground.

Is resistance infinite? 		 Go to Step 12. Repair short to ground wire circuit in communication wire circuit.
12  Check for short to power circuit in communication wire circuit 
  1. With ICM connector "G24" and ECM connector "E23" disconnected, turn the ignition switch to ON position.
  2. Check voltage between "G24-4" wire terminal at ICM connector and body ground.

Is voltage 0 V? 		 Go to Step 13. Repair short to power supply wire circuit in communication wire circuit.
13  Check for short of communication wire circuit 
  1. With ICM connector "G24" and ECM connector "E23" disconnected, check resistance between "G24-3" wire terminal and "G24-4" wire terminal at ICM connector.

Is resistance infinite? 		 Go to Step 14. Repair short of communication wire circuits.
14  ICM check 
  1. Check ICM referring to INSPECTION OF IMMOBILIZER CONTROL MODULE (ICM) AND ITS CIRCUIT .

Is ICM 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 .
scientia non olet · About LEMON Manuals