Passlock

What does Passlock do?  

Passlock/Vehicle Theft Deterrent(VTD) disables the fuel injectors(for~10min), stopping the vehicle from starting.  This happens when the wrong/damaged key is used or the ignition lock cyl has been tampered with.  There are also some common faults on these systems that can prevent you from starting your own vehicle.

Issues can be a damaged/failing sensor, module failure, key, wiring, etc.  One of the cheapest and best things if you have a worn key is to have a new one cut from the factory code(usually at the dealer).  There are some bypasses available(some border on insane with their pricing) or you can buy a replacement module(junkyard/online) if yours is bad.  Have seen some overpriced 'refurbished' modules listed as well, probably just plug them into a factory system to see if they work and sell them that way.  I would rather spend $5-40 at a local JY and test yourself or have it disabled in the PCM.  Some have had luck simply disconnecting the sensor wiring while the engine is running normally, definitely worth a shot!

IMO the absolute best and most reliable fix is to have it turned off in the PCM/ECM itself, that way the VTD doesn't ever disable the injectors.

Note that some of the ways that the sensor is connected to our vans varies over the years, in some cases where it's connected to the BCM(if you van has a BCM), and some cases the sensor is connected to the Passlock/EVO module.  

If you have a faulty module, it may act faulty and not give you the expected results.  So if your light is acting funky, it could be the module/power/ground/connectors/wiring.

What is up with this 'SECURITY' light?

The 'SECURITY' light works to tell you what is going on with your Vehicle Theft Deterrent system, while there may be some variance over the years here is the basic rundown.

• 1. Turns on when you turn the key to RUN, this bulb-check lets you know that the bulb is working.  If it doesn't come on then it's diagnostics time.

  2. Turns off shortly(~5seconds) after bulb-check, lets you know that everything is working normally.  Engine starts and runs fine.

  3. Turns on and doesn't turn off after bulb-check with the key in RUN. DTC set, read/record/clear codes.  Engine may not run.

  4. Turns on steady after starting vehicle to let you know that there is a problem detected after starting, while the engine was running.

  5. Flashes ON and OFF, problem detected during THIS key cycle, engine won't/might not start.

  6. Flashes during programming mode.

Passlock DTCs

• U1255 Class 2 Communication Malfunction -No MIL

  • U1301 Class 2 Data Link High -No MIL

  • U1016 Lost Communication with Engine Control System -No MIL

  • B3031 Security System Controller in Learn Mode -Security MIL

• B3033 Security System Indicates Tamper -Security MIL

  • B2958 Security System Sensor Data Circuit High -Security MIL

  • B2957 Security System Sensor Data Circuit Low -Security MIL

  • B2960 Security System Sensor Data Incorrect But Valid -Security MIL

• B2948 Security System Sensor Power Circuit High -Security MIL

• B2947 Security System Sensor Power Circuit Low -Security MIL

Cardone ProTech wrote:

GM vehicles have three types of Vehicle Thief Deterrent (VTD) systems, each requiring their own set of relearn procedures. Unless these procedures are correctly performed the vehicle will not start after the PCM has been replaced. The three systems are:

Vehicle Anti-Theft System (VATS), Passkey, & Passkey II – resistive chip ignition key

Passlock – coded lock cylinder

Passkey III – transponder ignition key

How do you know what system your vehicle has? Just look at the keys (see page 4). The sections that follow will help you identify the system and describe how to do the relearn.

VATS, Passkey, & Passkey II – resistive chip ignition key

Vehicle Anti-Theft System (VATS) – VATS has a separate module called the Theft Deterrent Module (TDM) that validates the resistive chip in the ignition key. If the resistance value read by the TDM is what the TDM is expecting, the TDM will send a signal to the PCM informing the PCM that a valid key is present and the PCM may start the vehicle. No relearn is required on a VATS equipped vehicle when replacing the PCM.

Passkey – The Passkey system has a separate module called the Theft Deterrent Module (TDM) that validates the resistive chip in the ignition key. If the resistance value read by the TDM is what the TDM is expecting, the TDM will send a signal to the PCM informing the PCM that a valid key is present and the PCM may start the vehicle. No relearn is required on a Passkey equipped vehicle when replacing the PCM.

Passkey II – The Passkey II system has the Theft Deterrent Module (TDM) function stored in the Body Control Module (BCM). The TDM portion of the BCM will validate the resistive chip in the ignition key. If resistance value read by the BCM is what the BCM is expecting, the BCM will send a message over serial data to the PCM informing the PCM that a valid key is present and the PCM may start the vehicle.

Cardone ProTech wrote:

Passlock – coded lock cylinder

The Passlock anti-theft system requires the presence of a key in the lock cylinder to enable starting. The lock cylinder contains a stationary Hall effect sensor and a rotating magnet. When the key is turned in the lock cylinder, the magnet creates a signal on the Hall effect sensor. The cylinder then sends a coded signal to the instrument panel cluster (IPC) or body control module BCM. If the IPC/BCM receives the expected coded signal, the IPC/BCM will send a message over serial data to inform the PCM that the vehicle may be started.

To perform a relearn on a Passlock system, make sure there is a fully charged battery in the vehicle. The battery will be used for 30 minutes without the alternator available for charging.

Connect a battery charger to the battery to ensure power is available while programming.

Both the IPC/BCM and PCM must be working and communicating with each other.

1. Turn ignition on.

2. Attempt to start the engine, and then release the key to the “ON” position.

3. Observe the “SECURITY” indicator light. After 10 minutes the “SECURITY” indicator light will turn off.

4. Turn ignition to the “OFF” position, and wait 10 seconds.

5. Attempt to start the engine, and then release the key to the “ON” position.

6. Observe the “SECURITY” indicator light. After 10 minutes the “SECURITY” indicator light will turn off.

7. Turn ignition to the “OFF” position, and wait 10 seconds.

8. Attempt to start the engine, and then release the key to the “ON” position.

9. Observe the “SECURITY” indicator light. After 10 minutes the “SECURITY” indicator light will turn off.

10. Turn ignition to the “OFF” position, and wait 10 seconds.

11. Vehicle has now learned the new password. Start the engine.

12. With a scan tool, clear any trouble codes.

NOTE: For most cars, one 10-minute cycle will be enough for the vehicle to learn the new password. Perform all 3 cycles if the car will not start after 1 cycle. Most trucks will require all 3 cycles for learning the password.

Cardone ProTech wrote:

Passkey III – transponder ignition key

The Passkey III anti-theft system uses a transponder inside the head of the ignition key. The exciter inside the ignition lock cylinder energizes this transponder when the ignition switch is turned on. The transponder transmits a unique signature to the theft deterrent control module. 

If the key signature transmitted is acceptable to the theft deterrent control module, the theft deterrent control module will transmit fuel enable password to the PCM. If the fuel enable password is correct, the PCM will start the vehicle.

To perform a relearn on a Passkey III system, make sure there is a fully charged battery in the vehicle. The battery will be used for 30 minutes without the alternator available for charging. 

Connect a battery charger to the battery to ensure power is available while programming. 

When performing this relearn, all previously learned keys will be erased. Additional keys may be relearned immediately after the first key has been learned by inserting the additional key and turning the ignition switch to on within 10 seconds of removing the previously learned key.

1. Insert a master key (black head) into the ignition switch.

2. Turn key to the “ON” position without starting the engine. Security light should turn on and stay on.

3. Wait for 10 minutes or until the security light turns off.

4. Turn key to the “OFF” position for 5 seconds.

5. Turn key to the “ON” position without starting the engine. Security light should turn on and stay on.

6. Wait for 10 minutes or until the security light turns off.

7. Turn key to the “OFF” position for 5 seconds.

8. Turn key to the “ON” position without starting the engine. Security light should turn on and stay on.

9. Wait for 10 minutes or until the security light turns off.

10. Turn key to the “OFF” position. The key transponder information will be learned on the next start cycle.

11. Start the vehicle. If the vehicle starts and runs normally, the relearn is complete. If additional keys need to be relearned:

12. Turn the key to the “OFF” position.

13. Insert the next key to be learned. Turn the key to the “ON” position within 10 seconds of removing the previously used key.

14. Wait for security light to turn off. It should happen fairly quickly. You may not notice the lamp, as the transponder value will be learned immediately

15. Repeat steps 12 through 14 for any additional keys.

Cardone ProTech wrote:

To perform a relearn on a Passkey II system, make sure there is a fully charged battery in the vehicle. The battery will be used for 30 minutes without the alternator available for charging.

Connect a battery charger to the battery to ensure power is available while programming. Both the BCM and PCM must be working and communicating with each other.

1. Insert ignition key and turn to the “ON” position. Do not attempt to start the engine. Leave the key in the “ON” position for approximately 11 minutes. The security light will be steady on or flashing for the 11-minute period. Do not proceed to Step 2 until the security light turns off or stops flashing.

2. Turn the ignition switch to the “OFF” position for 30 seconds.

3. Turn the ignition switch to the “ON” position as in Step 1 for 11 minutes.

4. Turn the ignition switch to the “OFF” position for 30 seconds.

5. Turn the ignition switch to the “ON” position as in Step 1 for 11 minutes for a third time.

6. Turn the ignition switch to the “OFF” position for 30 seconds for a third time.

7. Turn the ignition switch to the “ON” position for 30 seconds.

8. Turn the ignition switch to the “OFF” position.

9. Attempt to start the engine.

If the engine starts and runs, the relearn is complete.

Example late model wiring diagram:

Example 1998 Passlock Module wiring diagram: