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For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2000 🢒 Monte Carlo 🢒 Body and Accessories 🢒 Theft Deterrent 🢒 DTC B2957 Security System Sensor Data Circuit 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 data circuit.
    • This condition must be present during an engine start attempt, or for one second anytime after the engine has started.

Action Taken When the DTC Sets
    • The BCM stores DTC B2957 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 data circuit is shorted to ground when attempting to start the engine, the BCM does not send a message to the PCM via the Class 2 serial data link enabling the crank relay, and does not deliver fuel to the engine. The vehicle will exhibit an engine no-crank condition.
       - If the Passlock sensor data circuit is shorted to ground after the engine has started, the BCM enters fail-enable mode. During other attempts to start the engine, the BCM will send a 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
    • A current DTC B2957 clears when the BCM detects a valid Passlock sensor data voltage signal on the Passlock sensor data circuit.
    • A history DTC will clear after 100 consecutive ignition cycles if the condition for the malfunction is no longer present.

Diagnostic Aids

Test for a short to ground on the Passlock sensor data circuit or a short between the Passlock sensor data circuit and the Passlock sensor ground circuit. Refer to Circuit Testing in Wiring Systems

When BCM diagnostics and repairs are completed, refer to Powertrain On Board Diagnostic (OBD) System Check (3.4L) or Powertrain On Board Diagnostic (OBD) System Check (3.8L) in Engine Controls for additional information on PCM related DTCs that may be set during the diagnostic process.

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 short between the Passlock sensor data circuit and the Passlock sensor ground circuit.

    3.

  3. Tests for a short to ground in the Passlock sensor data circuit.

    4.

  4. Tests for 5V pull-up voltage output from the BCM in the Passlock sensor data circuit .

    5.

  5. Tests for a faulty PASSLOCK sensor that is internally shorted.

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 switch.
  2. Disconnect the BCM connectors C1 and C2.
  3. Use a digital multi meter (DMM) in order to measure the resistance between the Passlock sensor data circuit and the Passlock sensor ground circuit at the BCM harness connector C1.

Is the resistance measured greater than the specified value?

1000Kohms

Go to Step 4

Go to Step 6

4

Use a DMM in order to measure the resistance between the Passlock sensor data circuit and ground at the BCM harness connector C1.

Is the resistance measured equal to the specified value?

∞

Go to Step 5

Go to Step 8

5

  1. Disconnect the Passlock sensor electrical connector.
  2. Reconnect the BCM connectors C1 and C2.
  3. Turn ON the ignition switch.
  4. Use a DMM in order to measure the reference voltage supplied by the BCM on the Passlock sensor data circuit at the Passlock connector.

Is the voltage measured within the specified range?

4.5-5.5V

Go to Step 9

Go to Step 10

6

  1. Disconnect the Passlock sensor electrical connector.
  2. Use a DMM in order to measure the resistance again between the Passlock sensor data circuit and the Passlock sensor ground circuit at the BCM harness connector.

Is the resistance measured the same as the specified value?

∞

Go to Step 9

Go to Step 7

7

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

Is the repair complete?

--

Go to Step 11

--

8

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

Is the repair complete?

--

Go to Step 11

--

9
  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 in Instrument Panel, Gauges and Console.
  2. Perform the theft deterrent re-learn procedure. Refer to Programming Replacement Lock Cylinder, Body Control Module or Powertrain Control Module .
  3. Replace the BCM. Refer to Body Control Module Replacement .
  4. Setup new BCM. 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 11

--

10
  1. Test the BCM connectors for a poor electrical connection and repair as necessary. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
  2. If the BCM connection is OK, replace the BCM. Refer to Body Control Module Replacement .

Is the repair complete?

--

Go to Step 11

--

11
  1. Turn OFF the ignition switch.
  2. Reinstall connectors and components removed during the diagnostic process.
  3. Turn ON the ignition switch.
  4. 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 current BCM DTCs.
  8. Operate the system.

Are any current BCM DTCs present and are the repairs completed?

--

Go to Diagnostic System Check - Theft Deterrent

System OK