GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2000 🢒 Monte Carlo 🢒 Body and Accessories 🢒 Theft Deterrent 🢒 DTC B2947 Security System Sensor Power CKT Low

Object Number: 597558 Size: LF

Circuit Description

The Passlock theft deterrent system contains a Passlock sensor that is part of the ignition lock cylinder assembly. The body control module (BCM) provides voltage (B+) to the Passlock sensor through the Passlock sensor power circuit when the ignition switch is in the ACCESSORY, ON, or START position. The BCM also provides a 5-volt reference to the Passlock data circuit. The BCM provides ground to the Passlock sensor through the Passlock sensor ground circuit. The Passlock sensor interfaces with the BCM through the Passlock sensor data circuit.

When you turn the ignition switch to the START position with the proper key, the Passlock sensor applies a unique resistance value to the Passlock Data Circuit which pulls the 5-volt reference down to a unique voltage value, which is measured by the BCM. This voltage signal is unique and varies from vehicle to vehicle. When you attempt to start the engine, the BCM compares a previously stored (learned) voltage value with the circuit voltage value:

    • When the values match, the BCM sends a fuel enable password via the Class 2 serial data link to the powertrain control module (PCM). The PCM then enables the crank relay, and allows fuel delivery to the engine.
    • When the values do not match, the BCM sends a fuel disable password via the Class 2 serial data link to the powertrain control module (PCM). As a result, the PCM disables the crank relay, and does not allow fuel delivery to the engine.

Conditions for Setting the DTC

The BCM detects a short to ground on the Passlock sensor power circuit for one second, with the ignition switch in the ACCESSORY, ON, or START position.

Action Taken When the DTC Sets
    •  The BCM stores DTC B2947 in memory.
    •  The BCM sends a message to the instrument cluster to turn the SECURITY indicator ON.
    •  In addition, the BCM will take one of two actions:
       - If the Passlock sensor power circuit is shorted to ground when attempting to start the engine, the BCM will NOT send a message to the PCM to enable the crank relay, and to deliver fuel to the engine. The vehicle will exhibit an engine no crank condition.
       - If the Passlock sensor power circuit is shorted to ground after the engine has started, the BCM enters a fail-enable mode. Upon subsequent engine start attempts, the BCM will send a password message to the PCM via the Class 2 serial data link to enable the crank relay, and to deliver fuel to the engine. The engine will start.

Conditions for Clearing the DTC
    •  When a short to ground is no longer present on the Passlock sensor power circuit, the ignition switch must be cycled from OFF to ACCESSORY before this DTC can change from a current DTC to a history DTC.
    •  The BCM no longer detects a short to ground in the Passlock sensor power circuit.
    •  A history DTC will clear after 100 consecutive ignition cycles if the condition for the malfunction is no longer present.

Diagnostic Aids

Inspect for a short between the Passlock sensor power circuit and the Passlock sensor ground circuit, or a short to ground on the Passlock sensor power circuit. Refer to Circuit Testing and Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Test Description

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

  1. Always perform the Theft Deterrent diagnostic system check before attempting to diagnose this DTC.

    2.

  2. Tests for a short to ground in the Passlock sensor power circuit.

    3.

  3. Determines whether the BCM or the PASSLOCK sensor is internally shorted to ground.

    4.

  4. Perform the Setup New BCM procedure after repairs for proper BCM operation.

    5.

  5. Refer to the Theft Deterrent Re-Learn procedure after repair for proper BCM operation.

Step

Action

Value(s)

Yes

No

1

Was the Theft Deterrent diagnostic system check performed?

--

Go to Step 2

Go to Diagnostic System Check - Theft Deterrent

2
  1. Install a scan tool.
  2. Determine if the DTC is a history DTC.

Is the DTC a history DTC?

--

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the Body Control Module (BCM) connectors C1 and C2.
  3. Use a Digital Multi Meter (DMM) to measure the resistance between the Passlock sensor power circuit and ground at the BCM harness connector.

Is the resistance measured same as the specified range?

∞

Go to Step 4

Go to Step 5

4

  1. Reconnect the BCM connectors.
  2. Disconnect the PASSLOCK sensor electrical connector.
  3. Turn the ignition switch on.
  4. Use a DMM to measure the voltage between the PASSLOCK sensor power circuit and ground at the harness connector.

Is the voltage within the specified range?

B+ (10-14V)

Go to Step 7

Go to Step 6

5

Repair short to ground in the Passlock sensor power circuit. Refer to Circuit Testing and Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Is the repair complete?

--

Go to Step 8

--

6

  1. Turn OFF the ignition switch.
  2. Replace the BCM. Refer to Body Control Module Replacement .
  3. After replacing the BCM, perform the setup new BCM procedure. Refer to Body Control Module (BCM) Programming/RPO Configuration in Body Control System and Programming Replacement Lock Cylinder, Body Control Module or Powertrain Control Module .

Is the repair complete?

--

Go to Step 8

--

7

  1. Replace the ignition lock cylinder. The Passlock sensor is part of the ignition lock cylinder, therefore the Passlock sensor is not serviceable separately. Refer to Ignition and Start Switch Replacement .
  2. Perform the Theft Deterrent Re-Learn procedure. Refer to Programming Replacement Lock Cylinder, Body Control Module or Powertrain Control Module .

Is the repair complete?

--

Go to Step 8

--

8
  1. Turn OFF the ignition switch.
  2. Reinstall connectors/components removed.
  3. Turn ON the ignition switch.
  4. Use the scan tool to clear the BCM DTCs.
  5. Turn OFF the ignition switch.
  6. Turn the ignition switch to start, then to the ON position.
  7. Test for BCM DTCs.

Are any current BCM DTCs present?

--

Go to Step 2

System OK