Immobilizer System Diagnostic Troubleshooting Strategy

Use these steps to plan your diagnostic strategy. If you follow them carefully, you will be sure that you have exhausted most of the possible ways to find an immobilizer system fault.

1. Gather information about the problem from the customer.
2. Verify that the condition described by the customer exists.
3. Check the vehicle for any immobilizer system DTC.
4. If you cannot verify the condition and there are no immobilizer system DTCs, the malfunction is intermittent.
5. If you can verify the condition but there are no immobilizer system DTCs, or the system cannot communicate with Scan Tool MB991502, refer to DTC 12: ENCRYPTED CODES ARE NOT THE SAME OR NOT REGISTERED  and find the fault.
6. If there is an immobilizer system DTC, record the number of the DTC, then erase the DTC from the memory using Scan Tool MB991502.
7. Recreate the immobilizer system DTC set conditions to see if the same immobilizer system DTC will set again.
   • If the same immobilizer system DTC sets again, perform the diagnostic procedures for the DTC. See DIAGNOSTIC TROUBLE CODE CHART  .
   • If you cannot get the same immobilizer system DTC to set again, the malfunction is intermittent.