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ZZDaryl
ZZDaryl, Chevy Technician
Category: Chevy
Satisfied Customers: 12425
Experience:  28 year experience, Master Mechanic
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99 Tahoe: Wont start..fuel pump relay, then runs fine..Security light

Customer Question

I have a 99 Tahoe, 5.7 vortec. Won't start unless I jumper the fuel pump relay, then runs fine. Security light does not flash - I have done the 30 minute reset procedure. How do I diagnose/troubleshoot from here?
Submitted: 2 years ago.
Category: Chevy
Expert:  ZZDaryl replied 2 years ago.
Is there power to the fuel pump relay? If so how many terminals have voltage on them when the key is turned/cycled on?
Customer: replied 2 years ago.
Only at terminal 30, no power anywhere else.
Expert:  ZZDaryl replied 2 years ago.
Are you sure 85 or 86 is not getting voltage when the key is cylced on? It only gets voltage for 3 seconds if the engine does not start.
Customer: replied 2 years ago.
Was using a DVM, but didn't see any voltage swing. Initially truck would start momentarily then die after one sec, now it won't even do that while cranking so I am going to assume no voltage at all.
Expert:  ZZDaryl replied 2 years ago.
Do you know if the relay clicks when you cycle the key on?
Customer: replied 2 years ago.
Sorry, been away from the computer a few days.

Relay does not click when cycled on.
Expert:  ZZDaryl replied 2 years ago.

Ok if the relay is not getting voltage on terminal 85 or 86 (one or the other) there could be a broken wire between the computer and the relay so you would need to go to the computer and check terminal 1 on the C4 connector to see if it is getting voltage when the key is cycled on, if it is not the computer is most likely the cause of this problem, if it is getting voltage then there is a bad/broken wire between the computer and the fuel pump relay.

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