I have tried several times to fix this issues and it keeps coming back. My security light turned on for the first time on Sat night. I was planning on looking into it but I was really busy over the weekend and didn't think much of it, since the car was running fine.

Monday morning I get in my car to go to work and it doesn't start. It was throwing code P1631. I tried using my spare key and that didn't work either. I tried cleaning the pellet on the key and used some canned air in the ignition. After I did that the car started just fine but the light was still on.

Tuesday night it died again and stranded me in a parking lot. I found the 30 minute reset process where you wait 10 minutes for the security light to turn off and then do that 3 times. Car started right up and the security light turned off so I thought I had fixed it. It ran fine all day yesterday and then this morning it wouldn't start and it throws the code again!

I'm so frustrated right now. Does anybody have any other solutions? I really don't want to take it to the dealership.

 

Anybody have any ideas? I need the car this evening!

 

Check your battery-low voltage will send all kinds of gremlins into the system.

 

Any clues here?

DTC P1631
Circuit Description

The powertrain control module (PCM) controls the fuel injector operation and the starter operation based on a vehicle theft deterrent (VTD) password from the vehicle body control module (BCM). When the ignition is first turned ON, the BCM sends a programmed theft deterrent password to the PCM. The PCM acknowledges the password and responds to the BCM that normal fuel injector and starter operation will continue. If the PCM detects an incorrect password, a theft deterrent system failure, or an attempted vehicle theft, DTC 1631 will set. The engine will not start or crank as long as the condition is present.
Conditions for Running the DTC

The ignition is ON.
Conditions for Setting the DTC

The PCM detects an incorrect password from the VTD system.
The condition is present for less than 1 second.

Action Taken When the DTC Sets

The body control module (BCM) send a class to message to the instrument panel cluster (IPC) to illuminate the SECURITY indicator.
The PCM will not illuminate the malfunction indicator lamp (MIL).
The PCM will store conditions which were present when the DTC set as Failure Records data only. This information will not be stored as Freeze Frame data.

Conditions for Clearing the MIL/DTC

A History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
The DTC can be cleared by using a scan tool.

Diagnostic Aids

DTC P1631 indicates that the vehicle theft deterrent password that the PCM has learned does not agree with the password received from the VTD system. This condition can occur if an incorrect key is used when attempting to start the vehicle, or if the BCM has been replaced and the PCM Password Learn function has not been enabled. If the BCM has been replaced, the password must be relearned.

 

Programming Theft Deterrent System Components

Important

The body control module (BCM) must be programmed with the proper RPO configurations before performing learn procedures. Refer to Body Control Module (BCM) Programming/RPO Configuration .
If replacing the BCM with a GM Service Parts Operations (SPO) replacement part, the module will learn the passkey data code immediately. The existing PCM however, must learn the new fuel continue password when the BCM is replaced.
If replacing a PCM with a GM Service Parts Operations (SPO) replacement part, after programming, these modules will learn the incoming fuel continue password immediately upon receipt of a password message. Once a password message is received, and a password is learned, a learn procedure must be performed to change this password again. A PCM which has been previously installed in another vehicle will have learned the other vehicle's fuel continue password and will require a learn procedure after programming to learn the current vehicle's password.

Conditions

Use these procedures after replacing:

BCM
PCM

10 Minute Learn Procedure

Tools Required
Tech 2
Techline terminal with current SPS (Service Programming System) software

Connect the Tech 2 to the vehicle.
Select "Request Information" under "Service Programming".
Disconnect the Tech 2 from the vehicle and connect it to a Techline terminal.
On the Techline terminal, select "Theft Module Re-Learn" under "Service Programming".
Disconnect the Tech 2 from the Techline terminal and connect it to the vehicle.
Turn ON the ignition, with the engine OFF.
Select "VTD Re-Learn" under "Service Programming".
Attempt to start the engine, then release the key to ON (vehicle will not start).
Observe the SECURITY telltale, after approximately 10 minutes the telltale will turn OFF (the vehicle is now ready to relearn the password on the next ignition switch transition from OFF to CRANK).
Turn OFF the ignition, and wait 5 seconds.
Start the engine (the vehicle has now learned the password).
With the Tech 2 (scan tool), clear any DTCs.

30 Minute Learn Procedure

Turn ON the ignition, with the engine OFF.
Attempt to start the engine, then release the key to ON (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 password on the next ignition switch transition from OFF to CRANK).

Important

The vehicle learns the 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 password).
With a scan tool, clear any DTCs if needed (history DTCs will self clear after 100 ignition cycles).

 

My voltage seems fine. The DIC reads 11.5 before the car starts. I've done the wait 10 minutes to re-learn the key twice now and still no luck. It starts right after I do that but won't start the next time.

I have 4 codes:
P1630
P1631
B2721
B2735

So from what I've been reading I think I may need to replace the ignition lock cylinder. Can anyone confirm this?