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Gm Tech (Cam)
Gm Tech (Cam), GMC Mechanic
Category: GMC
Satisfied Customers: 1690
Experience:  GM Grand Master Technician 2007. 14 year experience.
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The anti theft light is on and won't come off my truck won't

Customer Question

The anti theft light is on and won't come off my truck won't crank or start I replaced the ignition switch the anti theft module and still nothing. It starts when I remove anti theft with a programer that a friend late borrow
JA: Have you checked the fuses? Have you tried to reset the computer?
Customer: Fuses are good. I tried to reprogram the key and nothing
JA: What is the model/year of your GM?
Customer: 2008 gmc sierra 3500hd lmm duramax
JA: Are you fixing your Sierra yourself? What have you tried so far?
Customer: Yes I have it a friend's shop that is a mechanic. I put the ignition switch theft deterrent exciter
JA: Anything else you want the mechanic to know before I connect you?
Customer: That's it
Submitted: 9 months ago.
Category: GMC
Expert:  Chad Farhat replied 9 months ago.

Hi, I'm Chad. Welcome to JustAnswer. I'm reviewing your question and I will be posting your reply ASAP.

Expert:  Pete replied 9 months ago.

New expert here.I apologize for the delay.

Have you had the fault codes checked/read out with scan tool that will plug in and communicate with all computers to see what codes are set with this issue here?

Let me know so we can continue,thanks Pete.

Customer: replied 9 months ago.
I did only gave me glow plug 2 and 5. The truck was running fine anit theft light came on for a second turned off truck ran good all day until I turned it off
Expert:  Pete replied 9 months ago.

O.k.,was the scan tool used one that can read the body control module for fault codes at all?Some scan tools will only read the engine computer.

Customer: replied 9 months ago.
The one i used can't let me try that
Expert:  Pete replied 9 months ago.

O.k.,you want to have the fault codes read out of the body computer.With this light on there should be at least one code set that will help diagnose and locate this issue.Is there any way you can get the codes read out using a scan tool that can read all computers?In some cases a local parts store might be able to read the body computer at no charge.

Let me know,thanks Pete

Customer: replied 9 months ago.
Let me get on it now.
Expert:  Pete replied 9 months ago.

O.k.,let me know what you come up with when your ready.

Thanks Pete

Customer: replied 9 months ago.
Computer said lost communication with body control system and lost communication with ecm/pcm
Expert:  Pete replied 9 months ago.

Are you able to read the PCM at all or the BCM and do you have code numbers for this message/issue here?

Customer: replied 9 months ago.
U0106, u0102, u0140
Expert:  Pete replied 9 months ago.

If you clear out these codes do they come right back again when trying to start the vehicle?Clear them then turn off the key and back on and try and start and see what happens then.