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DTC P1621: Immobilizer Communication Line Error: Troubleshooting

Step Action Yes No
1  Diagnostic Trouble Code (DTC) confirmation 
  1. Clear DTC(s) referring to DTC CLEARANCE .
  2. Turn ignition switch to OFF position.
  3. Check if any DTC is detected referring to 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 ECM (ENGINE CONTROL MODULE) REMOVAL AND INSTALLATION .
  2. Check for proper following terminal connections to ECM connector.
    • "E23-13" and "E23-28"

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 V? 		 Go to Step 7. Repair open in ground wire circuit.
7  Check for short to ground circuit in communication wire circuit
  1. With ICM connector "G24" and ECM connector "E23" disconnected, check resistance between "G24-4"/"G24-3" wire terminal at ICM connector and body ground.

Is resistance infinite? 		 Go to Step 8. Repair short to ground wire circuit in communication wire circuit.
8  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"/"G24-3" wire terminal at ICM connector and body ground.

Is voltage 0 V? 		 Go to Step 9. Repair short to power supply wire circuit in communication wire circuit.
9  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 10. Repair short of communication wire circuits.
10  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 ECM (ENGINE CONTROL MODULE) REMOVAL AND INSTALLATION .
  3. Check resistance between following terminal at ICM connector and ECM connector with ignition switch ON.
    • "G24-4" and "E23-13" ("PNK/BLU") wire terminal/"G24-3" and "E23-28" ("GRY/BLU") wire terminal

Is resistance infinite? 		 Repair open in communication wire circuit. Go to Step 11.
11  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 ECM (ENGINE CONTROL MODULE) REMOVAL AND INSTALLATION , and then perform PROCEDURE AFTER ECM REPLACEMENT . Replace ICM with new one referring to IMMOBILIZER CONTROL MODULE (ICM) REMOVAL AND INSTALLATION .
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