DTC P1621: Immobilizer Communication Line Error: Troubleshooting

WARNING: This page is about a different car, the 2011 Suzuki SX4. However, it is still accessible from the selected car via links, so may be relevant.

P1621: TROUBLESHOOTING CHART

Step	Action	YES	NO
1	Was "Immobilizer Control System Check" performed?	Go to Step 2.	Go to IMMOBILIZER CONTROL SYSTEM CHECK .
2	Fuse check Check fuse for ICM circuit. Is fuse in good condition?	Go to Step 3.	Replace blown fuse(s) and then, check for short to power circuit.
3	Voltage check at power and ground terminal Check power and ground terminal voltage of ICM connector referring to INSPECTION OF ICM AND ITS CIRCUIT . Is each terminal voltage in good condition?	Go to Step 4.	Repair circuit.
4	ICM and ECM connector check With the ignition switch at OFF position, check intermittent and poor connection of ICM connector and ECM connectors referring to INTERMITTENT AND POOR CONNECTION INSPECTION . Is each connector in good condition?	Go to Step 5.	Repair poor connection.
5	Communication circuit check between ICM and ECM Check for open, short and high resistance in serial communication and clock circuit between ICM and ECM. Is each communication circuit in good condition?	Substitute a known-good ICM and recheck. If DTC P1621 is still detected, substitute a known good ECM and recheck.	Repair circuit.