DTC P1638: Immobilizer Information Mismatched: 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.

P1638: TROUBLESHOOTING CHART

Step	Action	YES	NO
1	Was "Immobilizer Control System Check" performed?	Go to Step 2.	Go to IMMOBILIZER CONTROL SYSTEM CHECK .
2	Diagnostic Trouble Code (DTC) confirmation Disconnect negative (-) cable from battery for more than 5 seconds. Connect negative (-) cable to battery. Check if any DTC is detected referring to DTC CHECK . Is DTC P1638 still detected?	Go to Step 3.	Intermittent trouble check for intermittent referring to INTERMITTENT AND POOR CONNECTION INSPECTION .
3	ECM specification check Check ECM part number to see if ECM is applicable to the vehicle in service. Is a correct ECM used for the vehicle in service?	Go to Step 4.	Replace ECM with the correct one and recheck if DTC P1638 is still detected by ECM.
4	DTC check of ECM Check ECM for DTC referring to DTC CHECK . Is DTC U0073, U0101, U0121, U0140 and/or U0155 detected?	Go to applicable DTC troubleshooting.	Go to Step 5.
5	DTC check of BCM Check BCM for DTC referring to DTC CHECK . Is DTC U0073, U0100, U0101, U0144, U0151 and/or U0155 detected?	Go to applicable DTC troubleshooting.	Go to Step 6.
6	CAN communication circuit check Check for open, short and high resistance in CAN communication circuits between ECM and BCM. Is each CAN communication circuit in good condition?	Go to Step 7.	Repair circuit.
7	Replacement of BCM Replace BCM with new one referring to BCM REMOVAL AND INSTALLATION . Check ECM for DTC referring to DTC CHECK . Is DTC P1638 still detected?	Substitute a known-good ECM and recheck.	BCM faulty.