GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Epica 🢒 Engine 🢒 Engine Controls - 2.5L (LBK) 🢒 DTC P1628

Circuit Description

When the ignition switch is turned to ON, the ignition key is tested by the immobilizer anti-theft system. While the ignition key code is read by the theft deterrent control module, the engine can start to run with any key that will turn the lock cylinder. The key code is read and compared with key codes that have been stored in the memory of the theft deterrent control module. If a valid key is detected, the theft deterrent control module sends a serial data release message to the engine control module (ECM). Included in the release message is an identification (ID) code which assures that neither the theft deterrent control module nor the ECM have been substituted to defeat the system. If the ECM receives an invalid release message, the ECM performs the following action:

    • Disable the fuel injector circuit.
    • Disable the fuel pump circuit.
    • Disable the ignition coil.
    • If a communication link failure between the ECM and theft deterrent control module is detected, this DTC sets.

DTC Descriptors

This diagnostic procedure supports the following DTC:

DTC P1628 Theft Deterrent Fuel Enable Signal Not Received

Conditions for Running the DTCs
    • The ignition is ON or the engine is cranking.
    • The DTC P1628 diagnostic runs once per drive cycle.

Conditions for Setting the DTC

The ECM cannot communicate with the theft deterrent control module.

Action Taken When the DTC Sets
    • The control module stores the DTC information into memory when the diagnostic runs and fails.
    • The malfunction indicator lamp (MIL) will not illuminate.
    • The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records.
    • The engine control module disables the fuel system and the engine will not start.

Conditions for Clearing the DTC
    • A current DTC Last Test Failed clears when the diagnostic runs and passes.
    • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic.
    • Clear the DTC with a scan tool.

Diagnostic Aids
    • An open or a short in the serial data circuits of the theft deterrent control module can cause a DTC P1628 to set. The serial data circuit fault will also cause the following conditions:
       - The theft deterrent status will switch to Enable and the engine will crank but not start.
       - If there is a short circuit, the scan tool will not communicate with either the ECM or the TCM.
       - DTC P1628 will be stored in memory and is displayed by the scan tool when communication with the ECM resumes.
    • An intermittent electrical condition in the theft deterrent system can cause this code to set. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Test Description

The numbers below refer to the step numbers in the diagnostic table.

  1. If the engine starts and DTC P1628 resets, there is a condition with the theft deterrent detection coil or the ignition key transponder, continue diagnosis in theft deterrent.

    2.

  2. This step tests for ignition voltage to the theft deterrent module. The theft deterrent module cannot communicate with the ECM if there is no ignition positive voltage.

    3.

  3. This step tests for a good ground to the theft deterrent module. The theft deterrent module cannot communicate with the ECM if there is no ground circuit.

Step

Action

Yes

No

Schematic Reference: Theft Deterrent System Schematics

Connector End View Reference: Theft Deterrent System Connector End Views

1

Did you perform the Diagnostic System Check - Engine Controls?

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

  1. Turn ON the ignition, with the engine OFF.
  2. Clear the DTCs with a scan tool.
  3. Attempt to start the engine.

Does the engine start and idle?

Go to Diagnostic System Check - Theft Deterrent in Theft Deterrent

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the theft deterrent module electrical connector.
  3. Turn the ignition ON, with the engine OFF.
  4. Connect a test lamp between the Ignition 1 voltage circuit of the theft deterrent module and ground.

Does the test lamp illuminate?

Go to Step 4

Go to Step 6

4

Connect a test lamp between the ground circuit of the theft deterrent module and B+.

Did the test lamp illuminate?

Go to Step 5

Go to Step 7

5

Test for an intermittent and for a poor connection at the theft deterrent control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct a condition?

Go to Step 9

Go to Step 8

6

Repair the Ignition 1 voltage circuit of the theft deterrent module for an open or short to ground. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs in Wiring Systems.

Did you find and correct a condition?

Go to Step 9

--

7

Repair the ground circuit of the theft deterrent module for an open. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs in Wiring Systems.

Did you find and correct a condition?

Go to Step 9

--

8

Replace the theft deterrent control module. Refer to Theft Deterrent Module Replacement in Theft Deterrent.

Did you complete the replacement?

Go to Step 9

--

9
  1. Use the scan tool in order to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Attempt to start the engine.
  4. Observe the DTC information with a scan tool.

Did the engine start and run with no DTC P1628 set?

System OK

Go to Step 2