GM Electronic Throttle Body Circuit Descriptions And Testing Tips

TEST 2: Passlock Reset

If your GM pickup or SUV did have a PCM Ground circuit problem, then even after repairing the Ground issue, there's a good chance that it still won't start.

Specifically: The engine will crank, start, and then stall after a few seconds. You'll also notice that the Passlock symbol (usually the shape of a car with a pad-lock on it) on the instrument cluster is staying on or flashing, instead of turning off like it normally does.

This happens because the Passlock System has informed the PCM to activate its Fuel Lockout Cycle and disable fuel injection.

Resetting the Passlock system is not that hard to do, and you might already be aware of how to do it. If not, well this is what you need to do:

1. Crank the engine and let it stall.
2. Once the engine stalls, let the key in the RUN (On) position for 10 minutes.
   • You'll notice that the Passlock symbol on the instrument cluster will stay lit for these 10 minutes.
   • After 10 minutes the Passlock symbol will turn off.
   • These 10 minutes of down time (with the key On after a stall) is called a learn cycle.
   • You'll need to repeat the learn cycle (steps 1 thru' 2) a total of 3 times.
   • The Passlock system requires 3 consecutive lockout/learn cycles in order to complete its learn cycle (if you're not using the factory scan tool).
3. Once the Passlock symbol turns off, turn OFF the ignition and wait 5 seconds.
   • After 5 seconds, crank the engine once again and let it start and stall on its own. Let the key stay in the Run (On) position.
   • If it doesn't start, no big deal. Just release the key to the Run (On) Position.
   • The Key must remain in the Run (On) position for 10 minutes again.
   • As before, the Passlock symbol (on your instrument cluster) will stay illuminated for 10 minutes. After 10 minutes, it'll turn off.
   • This will be the second Passlock learn cycle.
4. Once the Passlock symbol turns off, turn OFF the ignition and wait 5 seconds.
   • After 5 seconds, crank the engine once again and let it start and stall on its own. Let the key stay in the Run (On) position.
   • If it doesn't start, no big deal. Just release the key to the Run (On) Position.
   • The Key must remain in the Run (On) position for 10 minutes again.
   • As before, the Passlock symbol (on your instrument cluster) will stay illuminated for 10 minutes. After 10 minutes, it'll turn off.
   • This will be the third Passlock learn cycle and third time's charm.
5. Once the Passlock Symbol has turned off (this 3rd time), turn the Key OFF (this is important) and wait 5 seconds before starting the engine.
6. Once the Passlock system has reset, you'll be able to crank the engine and it'll stay running (not to mention that the Passlock Symbol will not illuminate anymore).

Related Articles

You can find a complete list of 4.8L, 5.3L, and 6.0L test articles here: GM 4.8L, 5.3L, 6.0L Index Of Articles.

Here's a list of articles, you'll find there:

• How To Test The Crank Sensor (at: troubleshootmyvehicle.com).
• How To Test The MAF Sensor.
• How To Test The COP Coils.