DTC P1677
Diagnostic Instructions
DTC Descriptor
DTC P1677: Immobilizer System Disabled
Circuit/System Description
The body control module (BCM) sends the security code to the engine control module (ECM) via the serial data circuit. The ECM then sends a challenge to the BCM. Both the ECM and BCM perform a calculation on this challenge. If the calculated response from the BCM equals the calculation performed by the ECM, the ECM will allow vehicle starting.
Conditions for Running the DTC
Ignition is in the ACCESSORY or RUN position.
Conditions for Setting the DTC
The ECM is in reset state or is not programmed properly.
Action Taken When the DTC Sets
| • | The security indicator in the instrument cluster will illuminate. |
| • | Vehicle starting will be disabled. |
Conditions for Clearing the DTC
| • | A current DTC will be cleared when the ECM is programmed properly. |
| • | A history DTC will be cleared after 40 malfunction-free ignition cycles or when a scan tool is used to clear DTCs. |
Reference Information
Schematic Reference
Immobiliser Schematics
Connector End View Reference
Component Connector End Views
Description and Operation
Immobiliser Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
Note: Because of normal system communications between the BCM and ECM, any immobiliser B-codes must be diagnosed prior to the diagnosis of P-codes. See Diagnostic Trouble Code List.
Refer to Diagnostic Trouble Code (DTC) List - Vehicle .
Perform the Immobiliser Relearn procedure. Refer to Immobiliser System Component Programming .
| ⇒ | If the ECM does not complete the learn or vehicle starting remains disabled, replace the K20 Engine Control Module. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
Control Module References
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