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2007 Chevrolet Silverado 1500 - Problems starting

My pickup is fine when the key is in the on position but if I try to start it something under the hood clicks and I lose All power. Before trying to start there is 12 volts at the battery. After trying to start there is 5 to 6 volts at the battery. Disconnecting the battery seems to reset it.???

Your battery is likely toast. Have it tested at a parts store or service center. I suspect it will fail.

A jump start - jump pack or another car - should fire the car right up if the battery is bad but not internally shorted.

Possible bad crank sensor

Are you asking if that will reset or are you saying it did.

The crank sensor doesn’t come into play until AFTER the engine starts to crank.

Tester

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Did for Jeep and ford, I had the same issue before and crank sensor also tested good before start, struggled for a while until I just replaced the sensor and Wala problem solved

Let’s forget about the crankshaft position sensor for the time being . . .

How old is your battery?

Please tell us EXACTLY what type of battery you have . . .

I’m asking because there were actually 2 model year 2007 Chevy Silverado 1500 trucks

The old body style with the side-post group 78 battery

The new body style with the top-post group 49 battery

Which do you have?

If side-post, there is a very good chance your battery connections are either loose, stripped, corroded, or any combination thereof. Also take a very good look at the battery terminal bolt, once you’ve removed it. It’s very common for the threads to strip. If there’s any doubt, replace it. Any reputable auto parts store will have them in stock, they’re cheap.

First thing is to make sure none of the stuff in the preceding paragraph applies to you

If you tug on the battery wiring, and you can move the terminal end, relative to the battery post, you’ve got a poor connection. No ifs ands or buts. Correct it and try again

If the battery’s over 5yrs old, you should think of just replacing it right now. Consider it preventive maintenance. If it fixes your starting problems, great. If not, at least you can rule out a bad battery

Statistically . . . you’ve got a bad battery which will no longer hold a charge

The battery is brand new and tests good. Sorry I forgot to include that.

The battery is from Walmart. It was purchased in September of 2019. It is a 78 with side terminals. I have had it tested and all about the battery tests good. I hook up the battery, it has 12 volts, and all the bells and whistles work with the ignition switch key in the on position. As soon as I turn the key to the start position I lose all electrical power and the power goes to 6 volts at the battery. At that point I must disconnect then reconnect the battery to energize everything and I again get 12 volts at the battery terminals.

It sounds like the battery terminal ends are terribly dirty, clean the cable ends with a wire brush until the the metal is shiny.

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I have already cleaned cable ends and battery posts

Have you checked the connections on the other end of the battery cables? Could be a loose ground or bad connection at the starter, maybe. If nothing is found there, I guess I might look at relays next. If there’s an ignition relay or fuse, I’d swap it with a known good one bearing the same part #. Lastly, assuming the battery, cables, connections, and any associated relay is good, I guess I’d have the starter tested.

I have checked the battery cable ends at the starter and frame, they look good. I did go buy an OBad reader but have not had time to try it. I do thank every one who has helped. Thanks

I’d check relays next. Then test the starter. Disclaimer: I’m a shade tree / diy mechanic. Good luck.

If the battery measures 5-6 volts and corroded cables and posts aren’t the cause, the next step is to remove the battery and take the battery to a shop for a load or conductance test. That’s the only way to ascertain the condition of a battery. Even brand new batteries can be defective.