GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The Passlock System is provided in order to prevent vehicle theft if the ignition lock cylinder is forced to rotate. The Passlock controller reads the coded Passlock data signal. The data consists of a voltage generated by a voltage divider network created between the Passlock assembly and the Passlock controller. If the data is correct , indicating rotation of the lock cylinder with the proper mechanically cut key, the Passlock controller sends a password to the powertrain controller via serial data to indicate that engine starting should be allowed. The Passlock controller also interfaces with the driver displays subsystem to indicate, via a Security indicator, the Passlock subsystem status and acute subsystem failures.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B2958 Security System Sensor Data Circuit High

Conditions for Setting the DTC

    • The ignition switch is ON.
    • The body control module (BCM) signal input is greater than 4.9 volts for 1 second after turning the ignition switch to the CRANK position.

Action Taken When the DTC Sets

    • The DTC will set only when the engine is running
    • The security indicator will be ON.

Conditions for Clearing the DTC

    • The current DTC will clear once an ignition cycle has occurred without the fault recurring.
    • After 100 concurrent ignition cycles occur without the fault recurring, a history DTC clears.
    • Using a scan tool.

Diagnostic Aids

    • Inspect the Passlock sensor harness for an intermittent or a short to battery. Refer to Testing for Intermittent Conditions and Poor Connections .
    • You may be directed to this table from the VTD Diagnostic System Check without a DTC B2958 being set. If you were directed to this table, follow all of the steps in this diagnostic table.
    • When directed to this table, DTC B2958 may have a history status.

Test Description

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

  1. Test for a short to voltage on the ignition key resistor circuit.

  2. This step tests for a short to voltage on the off/run/crank voltage circuit.

Step

Action

Value(s)

Yes

No

Schematic Reference: Theft Deterrent System Schematics

1

Did you perform the Diagnostic System Check - Vehicle?

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Go to Step 2

Go to Diagnostic System Check - Vehicle

2

  1. Turn OFF the ignition.
  2. Disconnect the ignition switch connector.
  3. Back the ignition key resistor signal terminal from the ignition switch harness connector.
  4. Reconnect the ignition switch harness connector.
  5. Turn ON the ignition, with the engine OFF.
  6. With a DMM, measure the voltage at the ignition key resistor terminal.

Is the ignition key resistor signal circuit voltage greater than the specified value?

5 V

Go to Step 4

Go to Step 3

3

  1. Disconnect the ignition switch connector.
  2. Resecure the ignition key resistor signal circuit terminal into the harness connector.
  3. Reconnect the ignition switch harness connector.
  4. Disconnect the body control module (BCM) connector containing the off/run/crank voltage circuit.
  5. Back the off/run/crank voltage circuit terminal from the BCM harness connector.
  6. Reconnect the BCM harness connector.
  7. Connect a DMM between the off/run/crank voltage circuit terminal and a good ground.
  8. Important: Do not start the vehicle.

  9. Momentarily switch the ignition to the CRANK position. Do not start the vehicle.

Is the voltage measured at the off/run/crank voltage circuit greater than the specified value?

5 V

Go to Step 5

Go to Step 6

4

Inspect the ignition key resistor signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 11

Go to Step 6

5

Inspect the off/run/crank voltage circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 11

Go to Step 7

6

Inspect for poor connections at the BCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

--

Go to Step 11

Go to Step 8

7

Inspect for poor connections at the ignition switch. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

--

Go to Step 11

Go to Step 9

8

Replace the BCM. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 10

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9

Replace the ignition switch. Refer to Ignition and Start Switch Replacement .

Did you complete the replacement?

--

Go to Step 11

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10

Perform the Programming Theft Deterrent System Components procedure.

Is the repair complete?

--

Go to Step 11

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11

  1. Use the scan tool in order to clear the DTCs.
  2. Turn OFF the ignition.
  3. Turn ON the ignition, with the engine OFF.
  4. Select the body control module display DTCs function on the scan tool.

Does the DTC reset?

--

Go to Step 2

System OK