GM Service Manual Online
For 1990-2009 cars only

Object Number: 500717  Size: MF
Data Link Communications Components
Handling ESD Sensitive Parts Notice

Circuit Description

This circuit supplies the Passlock data to the Vehicle Control Module (VCM)/Powertrain Control Module (PCM) from the Passlock™ Module, as well as communicating all of the Class 2 messages among all of the modules and the tool, CKT 1807 (PPL).

Conditions for Setting the DTC

All of the following conditions must be met:

    • The ignition is active.
    • Communication with the Data Link Connector and other modules is lost or at least has been lost at one time due to intermittent connection (this is usually a DTC).

Action Taken When the DTC Sets

    • Stores DTC U1125 in the Passlock™ Module memory.
    • If the ignition was OFF at the time, the vehicle will not start again.
    • If the engine was running at the time, the vehicle will start again but the SECURITY indicator will remain illuminated.

Conditions for Clearing the DTC

    • The Passlock™ Module continuously monitors the signal and moves the DTC from current to history on the next ignition cycle when the condition causing the fault no longer exists.
        All Passlock™ Module history codes will be cleared after 100 ignition cycles (from OFF to RUN) with no current codes active during the 100 ignition cycles.
    • Using a scan tool.

Diagnostic Aids

    • When the diagnostics direct you to take electrical measurements at the Wiring Harness Junction Blocks, refer to Wiring Systems for terminal assignments of the Wiring Harness Junction Blocks.
    • If the DTC is a history DTC, the problem may be intermittent. Try performing the test shown while wiggling wiring and connectors, this can often cause the malfunction to appear.

Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

  1. The VTD Diagnostic System Check will test the scan tool's ability to communicate with the EVO/Passlock Module and the Vehicle Control Module VCM/PowertrainControl Module (PCM). If communications are unable to be establishedwith either module a CURRENT fault exists. This fault could be causedbya faulty power or ground circuit to the affected module, a faulty CKT 1807 (PPL), or a faulty control module. The VTD Diagnostic System Check table willdetermineif power or ground circuits are faulty. If the power and groundstest OK, you are referred to Diagnostic System Check - Data Link Communications to diagnose CKT 1807 (PPL)or a faulty EVO/Passlock Module.

  2. This step is to determine if the scan tool can use CKT 1807 (PPL) to communicate with the VCM/PCM.

  3. This step is to determine the problem with CKT 1807 (PPL). Whetherit is fault of the circuit or fault of the Passlock™ Module.

  4. In this step be sure to connect all connectors removed during the diagnosisand perform the reprogramming of the Passlock™ Module.

Step

Action

Value(s)

Yes

No

1

Was the VTD Diagnostic System Check performed?

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Go to Step 2

Go to Diagnostic System check in Theft Deterrent

2

  1. Turn the ignition switch to the ON position.
  2. Connect a scan tool to the Data Link Connector (DLC).
  3. Establish communication with the Vehicle Control Module (VCM)/Powertrain Control Module (PCM).

Does the scan tool communicate with the VCM/PCM?

--

Go to Step 3

Go to Diagnostic System Check - Data Link Communications

3

  1. Turn the ignition to the OFF position.
  2. Disconnect the Passlock™ Module.
  3. Connect a Digital Multimeter (DMM) between the terminal B4 of the Passlock™ Module and terminal 2 of the DLC.

Is the resistance below the specified value?

0-5ohms

Go to Step 4

Go to Step 5

4

Replace the Passlock™ Module.

Is the repair complete?

--

Go to Diagnostic System Check - Data Link Communications

--

5

Locate and repair the open or cause of resistance in CKT 1807 (PPL) between the Passlock™ Module and the DLC. Refer to Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Diagnostic System Check - Data Link Communications

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