Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
DTC Descriptor
DTC P1649: No Key/Security Code ProgrammedCircuit/System Description
The engine control module (ECM) and the body control module (BCM) are integral part of the vehicle theft deterrent system. The theft deterrent system authenticates the security code programmed into each of these modules to prevent unauthorised vehicle operation. This authentication process includes the following steps:
- When the ignition is turned ON or the door is unlocked by remote key the BCM and the key exchange security data to verify the correct key is used.
- Once the correct key has been confirmed and the ignition is turned ON, the BCM and ECM exchange data to allow the vehicle to start.
- The data exchange processes conducted use various encrypted data exchanges between each of the devices.
Important: If any of these authentication processes fail, the vehicle will not start and DTCs will set. For further information on the theft deterrent system, refer to Content Theft Deterrent (CTD) Description and Operation.
An immobilizer signal DTC sets if the theft deterrent system authentication process fails.
Conditions for Running the DTC
Ignition is in the ACC or ON position.
Conditions for Setting the DTC
| • | If the key is not programmed to the BCM then the key authentication will fail and the vehicle will be immobilized. |
| • | If the BCM is not linked to the ECM then ECM to BCM authentication will fail and the vehicle will be immobilized. |
| • | If the BCM, key or ECM have corrupt memory, then the authentication will fail and the vehicle will be immobilized. |
| • | If there is a fault with the GMLAN, no authentication will occur and the vehicle will be immobilized. |
Action Taken when the DTC Sets
DTCs P1649 is a type C DTCs.
Conditions for Clearing the MIL/DTC
DTCs P1649 is a type C DTCs.
Diagnostic Aids
Since a fault condition in a wiring connector may trigger DTCs, always test the connectors related to this diagnostic procedure for shorted terminals or poor wiring connections before replacing any component. Refer to Testing for Intermittent Conditions and Poor Connections.
The vehicle will allow engine cranking for up to 5 seconds. If the ignition key and BCM do not authenticate the ECM will cease engine cranking or if the engine has started it will stall. Subsequent engine cranking will not initiate unless the ignition is switched OFF for more than 5 seconds.
The "key" referenced in the DTC descriptor does not refer to the vehicle key. In this case "key" is referring to the challenge response.
Reference Information
Schematic Reference
Theft Deterrent System Schematics
Connector End View Reference
Description and Operation
Content Theft Deterrent (CTD) Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Testing
Important: Because of normal system communications between the TDM and ECM any theft deterrent B-codes must be diagnosed prior to the diagnosis of P-codes.
Perform the Programming Theft Deterrent System Components procedure. Refer to Theft Deterrent Control Module Programming and Setup. The ECM should successfully complete the password learn and the vehicle should start. If the ECM does not complete the learn or vehicle starting remains disabled, replace the ECM.Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
Control Module References for ECM replacement, setup, and programming
