Security alarm going off and engine will not start?

2004 GMC YUKON

210,000 MILES • V8 • 2WD • AUTOMATIC

KAYFAITH03

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1 POST
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One morning my battery was dead, so I got someone to boost me off. Once I was boosted off and my car was running, I noticed the security light flashing and about every minute or so it would beep four or five times like my car door alarm. So, I unhook the negative battery terminal from the battery for about 2 minutes and when I put the terminal back on my battery, my car sounded like an ambulance or emergency vehicle. Not like my regular door alarm sound but like an ambulance.I unhooked the negative terminal and the positive terminal from the battery and that's where I stand right now.

Nov 12, 2024 at 8:41 AM

WRENCHTECH

✓ASE Certified Mechanic
20,761 POSTS

Your truck has 2 security systems, an immobilizer and a contents security alarm.
Assuming no one has added an aftermarket alarm, this is how the factory alarm is deactivated.
Disconnecting the battery activates the alarm.

DEACTIVATING THE ALARM
In the alarm mode, the following conditions are true:
- The horns sound intermittently.
- The headlights and the parklamps are flashing.

In order to deactivate a system in the alarm mode, perform one of the following procedures:
- Use the key in order to unlock one of the doors.
- Press the door unlock button on the key fob.
- If the vehicle control module (VCM)/powertrain control module (PCM) receives a valid Passlock(R) ignition key rotation.

If this doesn't work, then it's likely someone has added an aftermarket system, and you will have to deal with whatever that is.

Nov 12, 2024 at 11:38 AM

Repair Safety Notice: This information is for general instructional purposes only. Vehicle repair can be dangerous. Verify all information, follow manufacturer service procedures, use proper tools and safety equipment, and consult a qualified repair shop when needed.