03 LB7 security light

dndj

Boost!
Apr 13, 2019
302
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Oregon
As you can see from my snippings, PCM / VCM Fail Enable is YES and the passlock state is Normal Decision.

Would a relearn fix this? I do recall doing one when I first got the truck many years ago....

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Ok, here's something from the FSM. Connect your Tech2. Turn the truck ON, momentarily rotate the ignition switch to the START position but let it return to ON before the truck can start. Scan the BCM for DTCs. Check the Passlock Data Voltage, as in the screenshot above, needs to fall between 0.86 and 4.28 volts. Also, the Passlock Code should be a number between 1 and 10. If the Passlock Code continues to say "Open", you have an issue with a connection or with your Passlock sensor itself in the key lock cylinder.
 

mojito5000

Member
Aug 20, 2019
36
3
8
Oregon
@dndj

I did as you suggested and I do get a valid code and the voltage is slightly below the cutoff (4.25). Could that voltage be too close to the cutoff for it?

I also started the truck afterwards and looked for any changes between the two screens and the only difference I noticed was VCM/PCM Fuel continue is off when the truck is not running, and is on when the truck is running. I've included a screen shot of the data while the truck is off.
 

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dndj

Boost!
Apr 13, 2019
302
34
28
Oregon
@dndj

I did as you suggested and I do get a valid code and the voltage is slightly below the cutoff (4.25). Could that voltage be too close to the cutoff for it?

I also started the truck afterwards and looked for any changes between the two screens and the only difference I noticed was VCM/PCM Fuel continue is off when the truck is not running, and is on when the truck is running. I've included a screen shot of the data while the truck is off.
Interesting. Your passlock sensor voltage is in range and there's a valid code so it would seem logical to look elsewhere.

Do the same thing, rotate to crank and release to ON position before vehicle starts, scan for DTCs. Look for ECM DTCs (including history DTCs) and BCM DTCs (also take a look at history codes). Reading BCM DTCs requires navigating down the Body menus on the Tech2 instead of Powertrain, I think.

VTD "fail enabled" means the VTD detected an electrical issue while the vehicle was running but won't activate and cause the no-start condition as it would in a true lock cylinder tampering theft situation. There should be a stored DTC for this somewhere. If not, I'm out of ideas. Doing an ECM-BCM password relearn procedure requires the truck to be in a VTD no-start condition so that wouldn't be an option. I had this exact same failure (security light ON, but truck runs) and ended up sending my ECM off for repair at SoCal diesel. Whatever magic they did worked.
 
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TahlulaMax13

New member
Jun 12, 2024
9
0
1
United States
Want to bring this thing back to life because I’m having the SAME issue and have been for 6 years. But with new emissions rules, I can’t pass smog now anymore because the code comes up before I can get the systems reset and they won’t smog it. (Yes, I hate CARB like everyone else).
 

beaker966

New member
Jul 10, 2024
1
0
1
Oconto Falls, WI
Wondering if anyone found out anything else with the security light on the dash but everything works issue? I have 03 LB7 with same issue. Plugged in with Snap-on Apollo scanner, won't communicate with theft deterrent system, but it will communicate with everything else. Had the truck for 4 yrs and the security light was on for about 2 1/2yrs. The light was on when I had a turner installed, was told it could be the radio (cause cd player didn't work),changed the radio and problem is still there. Help!
 

mojito5000

Member
Aug 20, 2019
36
3
8
Oregon
Light is still on, I've learnt to ignore it since it doesn't hurt anything. My cheap Chinese software based Tech2 stopped working, so I haven't been able to dig in anymore.