GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2006 🢒 GTO 🢒 DTC 🢒 DTC P1678

Circuit Description

After the ignition switch is turned to the ON position, and the powertrain interface module (PIM) has authenticated the body control module (BCM), the PIM sends an encrypted security code to the engine control module (ECM). The ECM compares the received security code with its own security code, and if it is valid, the ECM enables the vehicle to be started. If the security code received by the ECM is incorrect, DTC P1678 sets.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P1678 Immobilizer Powertrain Identification Failed

Conditions for Running the DTC

Conditions for running the DTC are:

    • The ignition is switched ON.
    • The ignition voltage is 10-16 volts.

Conditions for Setting the DTC

The ECM does not receive a valid response from the PIM when an attempt is made to start the engine.

Action Taken When the DTC Sets

When the DTC sets, the following action is taken:

    • The vehicle will not start during the current ignition cycle.
    • An immobilizer failed message is displayed on the instrument cluster multifunction display.

Conditions for Clearing the DTC

Refer to Diagnostic General Descriptions for information on the conditions for clearing DTCs.

Diagnostic Aids

Refer to Cruise Control Description and Operation for cruise control switch description, operation and inspection procedures. Refer to Cruise Control Schematics , Cruise Control Component Views , and Cruise Control Connector End Views . Refer to Testing for Intermittent Conditions and Poor Connections for intermittent fault conditions.

Test Description

  1. This step tests if the PIM and ECM have been linked together.

  2. This step ensures there are no problems within the ECM system that may cause DTC P1678 to set.

  3. This step tests the PIM ground circuits and supply voltage.

  4. This step tests the PIM harness connector for serviceability.

Step

Action

Yes

No

Schematic Reference: Cruise Control Schematics

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

2
  1. Switch the ignition to OFF for 30 seconds.
  2. Operate the vehicle within the conditions for setting DTC P1678.
  3. Using the scan tool, select the DTC display function.

Does DTC P1678 fail this ignition cycle?

Go to Step 3

Refer to Diagnostic Aids

3

Does DTC B3924 set at the same time?

Refer to Diagnostic Trouble Code (DTC) List - Vehicle to diagnose DTC B3924 first

Go to Step 4

4

Using the scan tool, perform the PIM Link to ECM procedure. Refer to Body Control Module (BCM) Programming/RPO Configuration .

Has the linking procedure performed correctly?

Go to Step 9

Go to Step 5

5

Check the engine control module (ECM) system. Refer to Diagnostic Starting Point - Engine Controls .

Has any fault been found and rectified?

Go to Step 9

Go to Step 6

6

  1. Test all ground circuits of the powertrain interface module (PIM) for a high resistance or an open circuit fault condition.
  2. Test the PIM ignition supply voltage circuit for a high resistance, an open circuit or a short to ground fault condition.

Has any fault been found and rectified?

Go to Step 9

Go to Step 7

7

Inspect for poor connections at the PIM wiring connector.

Has any fault been found and rectified?

Go to Step 9

Go to Step 8

8

Replace the PIM. Refer to Powertrain Interface Module Replacement .

Has the repair been completed?

Go to Step 9

--

9
  1. Using the scan tool, clear the DTCs.
  2. Switch the ignition to OFF for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the conditions for running the DTC.

Does DTC P1678 fail this ignition cycle?

Go to Step 2

System OK