Diagnostic Instructions
DTC Descriptor
DTC P1629: Theft Deterrent Fuel Enable Signal Not Received
Circuit/System Description
The theft deterrent module (TDM) sends the prerelease password to the engine control module (ECM) via the serial data circuit. The ECM then sends a challenge to the TDM. Both the ECM and TDM perform a calculation on this challenge. If the calculated response
from the TDM 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. |
| • | The ECM is not in learn mode. |
Conditions for Setting the DTC
The ECM receives does not receive the challenge response from the TDM within the required amount of time.
Action Taken When the DTC Sets
The security indicator will illuminate.
Conditions for Clearing the DTC
| • | A current DTC P1629 will be cleared when a challenge response is received. |
| • | A history DTC will be cleared after 40 malfunction-free ignition cycles or when a scan tool is used to clear DTCs. |
Diagnostic Aids
DTC P1629 is an indicator that the challenge/response was not received within the required time. This does not necessarily indicate a fault is present with the TDM or ECM. Factors such as a long engine crank, a delay in the serial data communication,
or B-codes set in the TDM will cause DTC P1629 to set. This DTC should not be used as a fault indicator, but rather as a symptom to assist in the diagnosis of these other systems.
Reference Information
Schematic Reference
Immobilizer Schematics
Connector End View Reference
Component Connector End Views
Description and Operation
Immobilizer Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References
for scan tool information
