No power to fuel pump

Tiny
LEFERINK
  • MEMBER
  • 2009 CADILLAC DEVILLE DTS
  • 4.6L
  • V8
  • 2WD
  • AUTOMATIC
  • 140,000 MILES
I have the vehicle listed above. Parked it at work. Went to start after an hour or so it would crank, but wouldn't start.
I knew enough to listen for the fuel pump (a slight humming noise), but heard nothing. So I replaced the pump. Still no start.

Some investigation online revealed that in many cases the fuel pump relay burns out. This was the case with this car too - the relay heated up. It melted the fuse block (under the rear seat) around one of the pins. The advice was to replace the fuse block. A little expensive, but an easy enough job. I replaced it - still no start!

I'm trying to think of what to check next. There is no power going to the pump. Nothing going to the fuel pump fuse. When I turn on the key, I hear the relay clicking, so it seems to work. The relay and all the fuses are new as they came with the now-replaced fuse block. But still no power to the pump.

My question is, is there another fuse/switch that deactivated the power to the fuel pump? It is the only thing that would make sense to me.
Sunday, June 7th, 2020 AT 2:27 PM

5 Replies

Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
If you have no power at the pump then we need to go to the fuel pump relay and check where we have power and how much power. If you remove the relay, you should have 12 volts all the time on pin 30. Then when you turn the key on you should have 12 volts on pin 85. Let's check this first and go from there because depending on this we will go in different directions.

Let me know if you have questions and we can go from there. Thanks.
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Sunday, June 7th, 2020 AT 2:47 PM
Tiny
LEFERINK
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Thank you for your quick reply! I'm in the process of getting a multi-meter because I don't have one yet. But I figured I would check it out with my test light first. With the key off I have power going to the 85 pin. There is no other power going to any other pin whether the key is on or off. Also I notice a difference in the configuration of the relay in the diagram compare to what I have. The 30-pin is not diagonal from the 85 as it says in your diagram. It is adjacent to it, as you can see in the picture posted.
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Monday, June 8th, 2020 AT 7:31 AM
Tiny
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  • MECHANIC
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So using your test light with the clip on ground and you touch terminal 30 and you have no power? If that is the case we need to find why. I suspect it is a wire issue or the rear fuse block as an open in it. That should have power all the time so clearly that is an issue. 85 should only have power when you turn the ignition on as that is the control feed from the PCM.
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Monday, June 8th, 2020 AT 8:24 PM
Tiny
LEFERINK
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  • 3 POSTS
Thanks for your help!
It turns out someone Frankensteined a different relay and inline fuse.
Working to restore it to the original condition.
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Tuesday, June 9th, 2020 AT 6:08 PM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Haha. That is great. Unfortunately that is the hardest issue we all have to deal with because there is no way to know if someone messed with it so you have to assume it is stock and just not acting properly.

Good work and thanks for the update.
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Wednesday, June 10th, 2020 AT 6:07 PM

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