B2957

Diagnostic Chart (Part 1 Of 2):

Diagnostic Chart (Part 2 Of 2):

Schematic:

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 Diagrams When BCM diagnostics and repairs are completed, refer to A Powertrain On Board Diagnostic (OBD) System Check (3.4L) or A 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.
3. Tests for short between the PASSLOCK sensor data circuit and the PASSLOCK sensor ground circuit.
4. Tests for a short to ground in the PASSLOCK sensor data circuit.
5. Tests for 5 V pull-up voltage output from the BCM in the PASSLOCK sensor data circuit.
6. Tests for a faulty PASSLOCK sensor that is internally shorted.