Engine Control Module (ECM)

When the ECM receives the CIM prerelease password, the ECM will challenge the password. The ECM sends this challenge back to the CIM via serial data. Both the ECM and CIM perform a calculation on this challenge. If the calculated response from the CIM equals the calculation performed by the ECM, the ECM will allow vehicle starting.

The ECM will disable vehicle starting if any of the following conditions occur:

• The prerelease password is invalid.
• The fuel disable password is sent by the CIM.
• No passwords are received: There is no communication with the CIM.
• The CIM calculated response to the challenge does not equal the calculation performed by the ECM.