Why does the fuel pump relay don't click when i turn the key to run? and why there is no power at the fuel pump relay?

So if you know the relay is good. Only 1 reason it won't work if you have power to it. And that's a bad ground or bad wire. The relay only click once when it first gets power and when power gets turned off and it's not loud. Not sure how your testing the parts. If you have power to your fuel pump. Is the fuel pump good and if it has a bad ground it won't work. What I do is get jumper cables to a battery and test the pump with two test leads to rule other things out. As for power from the relay. It only last while key is in the start position for 10 seconds then stops and while the engine is running. If you turn the key to run and then go test for power it may trip the relay since it's not running the engine. Hope that helps explain some things how it works. If you don't have oil pressure or low oil in the pan. The computer can also stop power to the pump so your engine won't run and destroy intself.

If you can't hear your fuel pump priming then either, the pump needs replacing or the relay. If you replace the relay and you still don't hear the pump prime then it's the fuel pump.

I just looked at a wiring diagram of the fuel controls for this model: there is no fuel shut-off switch in the wiring. It's pretty straight forward, typical fuel pump controls: the fuel pump relay is in the under-hood power distribution center. When this relay is turned on, power is sent to the fuel pump, nothing else is in the path of the hot wire to the pump module so it (the pump) should be working.

So if pump is not on, you can diagnose the wiring right here at the fuel pump relay. First you verify the power feed for the pump is available at the relay. (One terminal at the relay will have battery voltage with key off. If you pull the relay out and use a test light, one terminal position will be hot.) Next you verify the relay is working, sending power to the fuel pump in the gas tank. You do this by having someone cycle the key to on, while you hold a finger on the relay (it's back in place) to feel it click on. You should feel it, maybe even hear it, the relay will energize every time the key is turned to on, and this is what sends power to the fuel pump.` If it all works, and the pump is not on, the pump probably needs replacing. If the pump relay is not clicking on, that's a wiring hassle, including the wire to the engine computer. The pcm is what controls the relay turning on.
Do you know if the fuel pump has ever been replaced in the car? If it is original, it has been a good long run.

You said you hear the pump come on, then said fuel pump not running ???
Check the fuse for the pump, preferably with a test light to verify power is there. Key must be in on position. If the fuse is powered, feel for the fuel pump relay to click when you turn key to on. Put your finger on it while someone turns key to on. If it clicks, check for power at the tank connector on the pump wire, while the engine is cranked. If power there when cranking, the pump must have failed and needs replacing. If the relay clicked with key on, and no power at the pump wire at tank while cranking, then check wiring from relay to pump connector-the fuel wire may have broken.
If the relay doesn't click when key turned on, check for the power feed for the pump at the relay terminal. If the relay has power available to be transmitted to pump, then the relay's signal from the computer or the ground side of the relay's coil signal (from the computer) may need checked.
If the pump is working, and you have good pressure in the lines, check the injector circuit. Also a fused circuit, so check the fuse first. The injector should have a steady voltage signal to it with key on. The injector only has two wires, the power wire and the ground wire which goes to the computer. When the computer momentarily grounds the injector circuit, the injector "pulses", causing fuel to spray out the bottom.

There is a break in the wire that supplies power to the fuse box.
You need to trace this power wire from the fuse box to find the break in this wire and fix this wire,.
Ii would help you is you have a wiring diagram of your vehicle as the wires are color coded.

didnt specify year of vehicle most relays for tahoe is under hood and at side of dash on drivers side -- turn key to on and listen for hum of pump no hum try starting with starter fluid if starts test for power to connections ,pump and relay if power more than likely pump shot

check tank selector switch

Well for starters, you need to diagnose the problem before replacing anymore parts. I say this because you mention both the fuel pump and sensors dealing with the ignition system which are 2 separate main things. Basically it takes 2 things to make an engine start, fuel and spark at the spark plugs. You need to narrow down what is missing because it seems since you replaced sensors dealing with spark and then you mention the other need fuel. I'm not sure as to where to start to help until whatever is missing is diagnosed and then find the cause of the loss. There are a couple of things you can check. Below is a picture of the relay box in the engine compartment. With the help of somebody put a finger touching both the fuel pump relay and the EGI main relay. While touching them have somebody turn the key to the "on" position (no need to try and start). When the key is turned on you should feel a "click" inside both of those relays. The fuel pump relay will click for about 3 seconds and the click again to shut off. The EGI main relay should stay on. If both seem to be fine you need to make sure of the fuel pump gettting "juice" and for power to the ignition system like the coils. You can get to the power/juice wire at the fuel pump pretty easy. You can access the connection at the fuel pump by lifting the lower part of the rear seat. Once the seat is lifted you should be able to see a part in the carpet that is cut to be able to lift the carpet up and access the plate covering the access to the fuel pump and/or the top of the fuel tank. Using a test light, check the green and yellow wires at the fuel pump. You should have power at those wire when turn the engine over or if the key is just turned to the on position you should have power there for about 3 seconds. To begin checking for spark or power to the ignition system you need to make sure you are getting power to the ignition coils. The red and white wires at the coils are your power wires. Check those. Also you can check the power at the fuel injectors. When the key is turned on or when trying to start, you should have power to the green wire at each of the fuel injectors. You should have constant power/juice at each of the fuel injectors. This is where I would start to narrow down the loss. Start here with these tests and let me know how the tests come out by replying/commenting here or you can email me directly at [email protected] ith what you have found out. Once the first tests are done and I know what the results are, we can go to the next step with a couple of other tests to figue the problem out. If one of the relays don't "click" then you have a possible bad relay. The EGI main relay is a common thing to go as well as the fuel pump relay. Don't mind helping and there is no cost to you for it but I don't want to tell you to start replacing parts until the problem is located. Hope this helps get you started.

Did you do it like this? Voltmeter: black lead on negative battery terminal, positive lead on one of terminals on coil side- turn key to on, and see if there is voltage for about 2 seconds. If yes, check negative terminal of relay's coil side. If no voltage, move positive lead to other terminal for coil side. Turn key to on, and see if you have voltage for about 2 seconds. If yes, test negative side of relay's coil for good ground. If no signal at either terminal, the signal may be lost from the pcm.

When you turn the key to on, this will prime the fuel system-pump will turn on for only 2 seconds with key in on, and then if no crank signal, pump will turn off (the relay will not stay energized, so no power will go to pump). But when the engine is cranking over, the relay is energized, the coil side will stay powered as long as engine is cranking. After the engine is running, usually an oil pressure switch is tied into the fuel pump circuit, so the relay is no longer needed to put power to the pump. The pump will always be running when engine is cranking, and when engine is running, but the relay no longer is needed when engine is running. See?

Model? Year?

Check per owner manual to be sure inertia switch is not tripped. Remember, fuel pump only runs for 5 seconds when key is turned ON, then it shuts off if engine is not running. Pump always runs when key is in START position.
Listen for pump to run inside fuel tank for 5 seconds after key is ON.

The PCM power relay turns on the PCM and the PCM turns on the fuel pump relay, which turns on the fuel pump.

See owner manual forfuse & relay charts.