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Pete, Auto Service Technician
Category: Chevy
Satisfied Customers: 27814
Experience:  14 years GM dealer Technician.
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Security Light has been on for 3 days and truck will not

Customer Question

Security Light has been on for 3 days and truck will not start
JA: Does the light flash, blink or stay solid? Have you tried to reset the security system?
Customer: Stay solid
JA: What is the model/year of your Chevy?
Customer: 1999 GMC Sierra 1500 SL
JA: Are you fixing your Sierra 1500 yourself? What have you tried so far?
Customer: I replaced the battery and the light came on
JA: Anything else you want the mechanic to know before I connect you?
Customer: Nothing else
Submitted: 7 months ago.
Category: Chevy
Expert:  Pete replied 7 months ago.

Hi my name is ***** ***** I will be happy to assist with this today.In some cases I may need more info to assist better.I apologize for any delay.

There is a security relearn I can post here for you to correct this but first I need to know if this is the classic or new body style as 1999 both bodies were released.I can tell this by the engine liter size.Can you post what liter engine is in this model here and I will post the procedure you need below.

Thanks Pete

Customer: replied 7 months ago.
4.3 Liter
Expert:  Pete replied 7 months ago.

Try this procedure below as this should relearn the theft system.Do this with a fully charged battery.If a step is missed the procedure will need started over again.

1. Insure the ignition key is in the ON position.
2. Clear all EVO/passlock module and VCM/PCM DTCs. ( you can skip this step )

3. Momentarily rotate the ignition key to the CRANK position (Do NOT start the vehicle), then release it to the RUN position (Do NOT key OFF in the process).
4. Wait 10 minutes. Observe the SECURITY indicator.

5. The SECURITY indicator will transition from flashing to ON briefly to OFF after 10 minutes if remaining in the ignition ON position.
6. Turn the ignition switch to the OFF position and wait for 10 seconds.
7. Repeat steps 3 through 6 two more times. The new security code is ready to be communicated among the Passlock sensor, EVO/Passlock module and VCM/PCM. The new password ***** ***** on the next ignition lock cylinder cycle from OFF to CRANK to ON (start attempt).The engine should now start.

If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service,your 5 star rating is appreciated.You can rate at any time and we can continue to work on your question as this will not close out your question.Keep in mind in some cases it can be difficult to fully diagnose or help repair your vehicle without seeing it and I work on delivering the best possible answer from what I see to work with.

Thanks Pete