Immobilizer System Diagnostic Troubleshooting Strategy

Use the following steps to plan your diagnostic strategy.

1. Gather information about the problem from the customer.
2. Verify that the condition as described by the customer exists.
3. Check the vehicle for any immobilizer system DTCs.
4. If you cannot verify the condition and there are no immobilizer system DTCs, the malfunction is intermittent. Refer to "How to Use Troubleshooting/inspection Service Points - HOW TO COPE WITH INTERMITTENT MALFUNCTIONS " .
5. If you can verify the condition but there are no immobilizer system DTCs, or the system cannot communicate with scan tool MB991958, refer to SYMPTOM CHART  and find the fault .
6. If there is an immobilizer system DTC, record the DTC, then erase it from the memory using scan tool MB991958.
7. Recreate the immobilizer system DTC set conditions to see if the same immobilizer system DTC will resets.
   1. If the same immobilizer system DTC resets, perform the appropriate diagnostic procedure. Refer to DIAGNOSTIC TROUBLE CODE CHART  .
   2. If the same immobilizer system DTC does not reset, the malfunction is intermittent. Refer to "How to Use Troubleshooting/inspection Service Points - HOW TO COPE WITH INTERMITTENT MALFUNCTIONS " .