Passlock theft deterrent: starts then stalls / no-start with security lamp

Why it happensA magnet in the ignition cylinder produces a unique voltage across a Hall effect sensor in the ignition housing; the BCM and lock cylinder enable starting.

The GM VTD or Passlock system uses the body control module (BCM) and ignition lock cylinder to activate the start function. The ignition cylinder uses a magnet that produces a unique voltage value when rotated in the ignition housing across the Hall effect sensor.— [1]

Why it happensIf the voltage matches the stored value, the BCM signals the PCM to enable fuel.

The BCM compares this voltage value to the value stored in the BCM. If the voltage values are the same, the BCM sends a signal to the powertrain control module to enable fuel.— [1]

First signsIf the values do not match, the engine briefly starts and then stalls.

If the voltage values are not the same, the engine will briefly start, then stall.— [1]

How to confirmA security lamp flashing after an attempted start means the fuel disable command is active.

The quickest way is to look at the security indicator lamp on the instrument panel. If it’s flashing after an attempted start, the fuel disable command has been energized.— [1]

How to confirmA scan tool parameter showing 'fuel system disabled' or similar indicates a Passlock issue.

If the parameter shows “fuel system disabled” or a similar description, then it’s a Passlock issue.— [1]

First signsThe DTC present was P1631, Theft Deterrent System - Password Incorrect.

The DTC present is a P1631— ”Theft Deterrent System – Password Incorrect.”— [1]

First signsThe BCM stored B2960, which relates to the BCM monitoring the Passlock data voltage.

In this case, a B2960 was stored, which relates to the BCM monitoring the Passlock Data Voltage.— [1]

How to confirmMonitor the Passlock Data Voltage for approximately one minute; the voltage value should not change by more than .02 volt.

The diagnostic flow chart for this DTC recommends monitoring the Passlock Data Voltage for approximately one minute. The voltage value should not change by more than .02 volt.— [1]

Why it happensIn the article's case the ignition housing was the cause; the connections between the housing and the BCM should also be checked.

The ignition housing was the cause in this case. Also check the connection points between the ignition housing and BCM.— [1]

How to confirmIf the voltage does not change from 5 volts, check the ignition housing.

If the voltage does not change from 5 volts, check the ignition housing.— [1]

CautionLoss of Ignition 1 voltage to the BCM gives the same start-then-stall behaviour.

If Ignition 1 input voltage is lost, the engine will start briefly, then stall— similar to the behavior when an incorrect password is detected.— [1]

CautionIn that case no BCM Passlock DTCs will be present because the Passlock software was not initialized.

But when you check for BCM Passlock DTCs, none will be present, because the Passlock software was not initialized.— [1]

Applies toThe article's example data was captured from a 2000 GMC Denali.

Fig. 1 on this page is a Vetronix Tech 2 screen capture taken from a 2000 GMC Denali, using the Powertrain section.— [1]

Applies toA remote start/stop system will not function with the current Passlock Theft Deterrent on 2003 and beyond C/K trucks.

This procedure is required because a remote start/stop system will not function with the current Passlock Theft Deterrent on 2003 and beyond C/K trucks.— [2] p. A-28/A-29, Passlock Interface For Remote Start/Stop

Why it happensA start attempt by any means other than turning the key in the ignition switch is treated by the truck body computer as theft and the fuel injectors are disabled.

If an attempt is made to start a vehicle by a means other than a key rotation in the ignition switch, the Truck Body Computer ( TBC) will interpret this start request as a vehicle theft and disable the fuel injectors.— [2] p. A-28/A-29, Passlock Interface For Remote Start/Stop

Applies toBulletin 01-08-56-002 applies to 1999-2001 Chevrolet and GMC C/K Pickup and Utility Models with DTC B2960 set.

01-08-56-002; Security Lamp Illuminated on IP, Engine Stalls, No Start, DTC B2960 (Security System Sensor Data Incorrect but Valid) Set (Inspect and Repair Cause of DTC B2960); 1999-2001 Chevrolet and GMC C/K Pickup and Utility Models— [3]

RepairThe condition is the Security lamp illuminated on the instrument panel, engine stalls or no start, with DTC B2960 (Security System Sensor Data Incorrect but Valid) set; the correction is to inspect and repair the cause of DTC B2960.

Security Lamp Illuminated on IP, Engine Stalls, No Start, DTC B2960 (Security System Sensor Data Incorrect but Valid) Set (Inspect and Repair Cause of DTC B2960)— [3]