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Hey all, been following on the site for some time now, never posted anything since I cant give any useful knowledge like everyone else on here. Anyways, i have an 04 LB7, the pass lock light has been on on the dash for quite some time, never stopped it from firing up or anything like that, but it's really starting to annoy me. Anyone have any idea how to shut it off? Thanks in advance
 

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DTC P1631

CIRCUIT DESCRIPTION
The class 2 serial data circuit is used in order to communicate between the powertrain control module (PCM) and the vehicle theft deterrent (VTD) body control module (BCM) systems.

When the Passlock portion of the VTD system has sensed the proper operation of the ignition switch and lock, or determined that the switch and lock have not been tampered with, the BCM transmits a password to the PCM. Fuel delivery is enabled if this password matches the password stored in the modules memory. If a component in the theft deterrent system has been replaced, the modules need to relearn the password of the new components. If the relearn procedure was not performed, this DTC will set.

If a VTD failure occurs during an ignition cycle that the PCM has enabled fuel, then the BCM will enter a fail-safe mode: Fail Enable VTD System Failure with Fuel Enabled. The BCM remains in Fail Enable Mode, for the current and future ignition cycles, until the fault is corrected and a valid password is received, or until battery power is removed. If the battery is disconnected or the codes are cleared, the vehicle will lose its Fail Enable status and will not start until the fault is corrected, the 10-minute timer expires, and the PCM receives the correct fuel delivery password.

DTC DESCRIPTOR
This diagnostic procedure supports the following DTC:
DTC P1631 Theft Deterrent Fuel Enable Signal Not Correct

IMPORTANT: Do not clear DTCs unless directed by a diagnostic procedure. Clearing DTCs will also clear valuable Freeze Frame and Failure Records data.



•If the PCM is replaced, the PCM must re-learn a valid password and crankshaft variation.
•If the BCM is replaced, the PCM must re-learn a valid password.
•Check for published service bulletins relating to exhibited symptoms or component operation.
•If the vehicle does not start, or starts and stalls:
•Turn OFF the ignition and wait at least 5 seconds before trying to restart.
•If a fault or tamper has been detected, the BCM will not forward the correct password to the PCM for a period of 10 minutes , even if the condition is corrected during that time period. This may cause a DTC P1631 to set in the PCM. This timer can be monitored in the Passlock Data parameter of the scan tool. Once the time has elapsed, the BCM will determine if the condition is still present.
•The PCM and BCM parameters can be monitored with a scan tool.
•The Passlock state and the auto learn timer can be viewed in the Passlock Data parameter of the scan tool.
•Inspect the following for preventing the Passlock sensor from communicating with the BCM:
•Passlock sensor
•Ignition switch assembly
•Passlock sensor circuitry
•Bent pins at the small Passlock sensor
•If this DTC sets along with a DTC B2960, then the problem was caused by malfunctioning Passlock components or circuitry, not the PCM.
•Inspect all related wiring and connections including the PCM and BCM connections. These may cause an intermittent malfunction.
•An intermittent may be caused by any of the following conditions:
•A poor connection
•Rubbed through wire insulation
•A broken wire inside the insulation
•Thoroughly inspect any circuitry that is suspected of causing the intermittent complaint.
 

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Discussion Starter #4
thats one hell of a write up, so basically i should start by checking all the wiring under the dash, make sure nothing was compromised, and go from there?
 

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Ha Ha , I had it saved from someone else- does give you some reading and understanding how it works. To cold out anyway! Here is the relearn--
30 Minute Learn Procedure
Turn ON the ignition, with the engine OFF.
Attempt to start the engine, then release the key to ON; the vehicle will not start.
Observe the SECURITY telltale; after approximately 10 minutes the telltale will turn OFF.
Turn OFF the ignition, and wait 5 seconds.
Repeat steps 1 through 4 two more times for a total of 3 cycles/30 minutes; the vehicle is now ready to relearn the Passlock Sensor Data Code and/or passwords on the next ignition switch transition from OFF to CRANK.

Important
The vehicle learns the Passlock Sensor Data Code and/or password on the next ignition switch transition from OFF to CRANK. You must turn the ignition OFF before attempting to start the vehicle.


Start the engine. The vehicle has now learned the Passlock Sensor Data Code and/or password.
With a scan tool, clear any DTCs, if needed. History DTCs will self clear after 100 ignition cycles.



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After replacing the ignition switch...

Turn the key and attempt to start the car, it won't. It should just crank once.
Wait 10 minutes. The passlock light should be flashing and the DIC will say "Service Vehicle" during that 10 minute span.
After 10 minutes has passed, turn off the car, count to 10, and try to start it again.
Wait another 10 minutes.
After 10 minutes, turn car off 10 seconds and try to start again.
Wait another 10 minutes.
After 10 minutes, turn car off 10 seconds and try to start again.
It should start up this time. The passlock has been learned.
 

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Discussion Starter #6
I'll have to try the key cycle thing soon, I tried it once in the past but it didn't work, iprobably did bit wrong, thanks for the help, ill keep you updated once I try it
 

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tried the 30 minutes procedure, waited about 15 minutes for the light to go off with key in the on position, never happened...any other ideas??
 

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My 2007.5 new body Duramax (same as 2008) also keeps blowing the 2 amp dlis fuse. Chamuco, did you ever figure this out? Mine just started doing this.
 

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Hey all, been following on the site for some time now, never posted anything since I cant give any useful knowledge like everyone else on here. Anyways, i have an 04 LB7, the pass lock light has been on on the dash for quite some time, never stopped it from firing up or anything like that, but it's really starting to annoy me. Anyone have any idea how to shut it off? Thanks in advance
well.... theres a couple of things you can do. first off the light should not be on while running. There could be a couple reasons its on though.

If the truck has an old remote start installed in it:

Some installers will cut the R code wire and permenently bypass the cylinder resistor with a 1/4w resistor of the correct-ish value. The R code has to be within 10% of the expected value to enable starting. If this value is not detected at some point it will set the light. Resistors will drift slightly as they age, and based on temperature so if its permenently bypassed it could be the resistor failing. IF YOU HAVE THIS BYPASS INSTALLED IT SHOULD BE REMOVED AND RE-WIRED CORRECTLY.

There are 2 correct ways to bypass the cylinder resistor using relays. Method 1 will use 1 relay, and will set the security light when the truck switches from remote start to the key. The solution to this is to re-wire the truck with a 2 relay bypass (there is a diretech tech document on this)

If the truck does not have a remote start, or has a remote start using a data module connected to the purple J1850 wire at the OBDII:

In this case, i would pull the steering shroud apart (very easy) and inspect the R code wires for any breaks in the insulation or pinches.

The system is designed to self calibrate the drift in Rcode over time, however if the code changes too quickly, it will set the light. If the code is wrong, staring will be disabled, but if the code is within range, it will still start but set the code to get the system checked. You can re-calibrate the Rcode by doing a passlock relearn procedure on the truck. It will take about 45 minutes to complete and requires a good quality battery charger to be connected to the truck, as you will be leaving the ignition on, engine off for about 45 minutes.

The procedure for this has been covered elsewhere on this forum in detail.

Edit: Did not realize this was almost a decade old... oh well, maybe this will help someone else.
 

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My 2007.5 new body Duramax (same as 2008) also keeps blowing the 2 amp dlis fuse. Chamuco, did you ever figure this out? Mine just started doing this.
IIRC this fuse powers the PK3 module and the key cylinder lock solenoid, is there anything tapped into it for aux power? there should be NO aftermarket accessories tapped into a 2007.5 or newer trucks ignition wires.
 

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I did have an aftermarket remote starter but had this removed right away when I first started blowing the 2 amp fuses. This was done by dealership. Since then, the issue continued so I had to go back to dealership. They switched out the anti-theft module. Charged me a whole bunch of money to reprogram the module and to relearn 3 keys. I'm not 100% sure if the issue is fixed but I sure hope so. This was an intermittent problem so I won't know if that was the issue. Will have to give it some time.
 

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Had the Anti theft module replaced at dealership. Took some time to relearn the module and then the truck keys. Cost me a bundle. So far so good.
 

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Had the Anti theft module replaced at dealership. Took some time to relearn the module and then the truck keys. Cost me a bundle. So far so good.
I do vaguely remember something about a TSB for defective PK3 modules but its been so long i could me mixing up years or models. Ive seen that fuse blow more than a few times in situations that it should not so your not alone. FYI, if the key ever gets stuck in the ignition, and you cant pull it out, its because that fuse is blown.
 
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