SPONSORED LINKS

No power to fuel pump, weird voltages at fuse box

Tiny
HAMFIST
  • MEMBER
  • 2008 CHEVROLET EXPRESS
  • 5.3L
  • V8
  • 4WD
  • AUTOMATIC
  • 166,553 MILES
Got some weirdness. Everything pointed to a fuel pump. No pressure at the schrader valve on the fuel rail. 12v at the relay, 0 ohms over to the 20a fuse. The other terminals of the relay get 5vdc when the key is turned to crank.

Cut hole in floor of van (i have no lift), replaced pump. Same issue. Checked wiring at pump, no voltage at the pump!

Digging deeper, changed with known good relay, same result, confirmed the 30 spade gets 12vdc. Jumped 30 and 87, confirmed 12vdc at the fuse, and fuse good.

Here's the weirdness: When the key is off and out, both terminals of that fuse are seeing 4-5vdc. When the relay is back in and the key is turned im only getting 7-8vdc. I don't know if it is related or not. When I am trying to take apart the fuse box with the 3 10mm bolts, when they are all loose, nothing works, dash dead, key gets nothing. Should those bolts control the power flow of that whole fuse box? How does that box come apart?

I'm thinking corrosion in the box. What else can I test?
SPONSORED LINKS
Friday, August 6th, 2021 AT 8:22 AM

14 Replies

Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
I think you are exactly correct. There is resistance in either the wiring or the control panel/circuit board.

I am attaching the wiring diagram below and the fuse layout if you need (appears you don't).

Unfortunately the manual does not include a process on how to disassemble the fuse box as that is not a common repair. The OEM just recommends replacing it if there is an issue.

However, if you are removing the relay and still have voltage on the fuse 2 then you have a short on the circuit board that is allowing voltage through even though the connection is supposed to be remove.

https://www.2carpros.com/articles/how-to-check-wiring

https://www.2carpros.com/articles/how-a-car-electrical-system-works

What I would do in this case is just wire in an external relay. Basically if there is an issue with this board then you don't need the relay to run through it. You can just take each of these wires and cut them going in and out of the fuse block and wire in your own relay and fuse so that it avoids the issue.

If you are interested in doing this, let me know and we can help with questions. However, there are many kits out there. I included a picture of one below.
Images (Click to make bigger)
Thumb
Thumb
Thumb
Thumb
Thumb
Thumb
Thumb
Thumb
Thumb
SPONSORED LINKS
Was this
answer
helpful?
Yes
No
+1
Sunday, August 8th, 2021 AT 9:41 AM
Tiny
HAMFIST
  • MEMBER
  • 64 POSTS
Finally got back at it. Removed fuse box, looked dirty with water traces. Disassembled the box down to the board. Used electrical cleaner and canned air to remove all contaminants.

Fuel pressure at rail, and started on second attempt.

Corrosion and sediment to blame.
Was this
answer
helpful?
Yes
No
Monday, August 23rd, 2021 AT 7:45 AM
Tiny
HAMFIST
  • MEMBER
  • 64 POSTS
And, it shut off at the bottom of the hill. Randomly restarts. Only runs for a few moments with jump pack.

Hmmm
Was this
answer
helpful?
Yes
No
Monday, August 23rd, 2021 AT 8:19 AM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
That is interesting. Where exactly did you find the corrosion?

I suspect that is still the issue. I bet if you check the fuel pressure it will be low. Then if you check the voltage at the pump, that will be low as well. Which points to more corrosion or the connections are just not salvable.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

I attached the wiring diagram below but try using starter fluid in the intake. It may fire without the jump box on it and if it does then that is the issue.
Images (Click to make bigger)
Thumb
Thumb
Was this
answer
helpful?
Yes
No
Monday, August 23rd, 2021 AT 5:27 PM
Tiny
HAMFIST
  • MEMBER
  • 64 POSTS
Yeah, you are correct. I have ordered a new fuse box for it.
SPONSORED LINKS
Was this
answer
helpful?
Yes
No
Tuesday, August 24th, 2021 AT 6:37 AM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Sounds great. Please let us know how this turns out. Thanks for the updates and coming back to keep us updated. That will surely help others in the future. Thanks again.
Was this
answer
helpful?
Yes
No
Tuesday, August 24th, 2021 AT 6:15 PM
Tiny
HAMFIST
  • MEMBER
  • 64 POSTS
New fuse box cured all that ales it. Then I had an ale.
Was this
answer
helpful?
Yes
No
Wednesday, August 25th, 2021 AT 1:37 PM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Haha. That is great. Drink one for me. Thanks for updating us and providing the solution for others as that will surely help others.

Thanks for using 2CarPros.
Was this
answer
helpful?
Yes
No
Wednesday, August 25th, 2021 AT 4:34 PM
Tiny
HAMFIST
  • MEMBER
  • 64 POSTS
And it shut off again, this time at a Chevrolet dealership. Said the fuse box was bad. Showed them the receipt, they said oh, well we can't get another one, chip shortage.
Was this
answer
helpful?
Yes
No
Monday, September 27th, 2021 AT 11:41 AM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Oh wow. That is unbelievable.

Just to make sure they are not conveying an incorrect message. As long as the part is not discontinued, they will get one it just won't be soon. They will most likely have to put it on order and it will get released when they do have them.

However, if it were me, I would not wait as that could be months.

What I would do is get the part number and then start contacting salvage yards. I am sure you will find one out of another vehicle as this was a widely produced vehicle and more than likely they used this part in many different trucks and vans. So as long as it is the same part number it will work.
Was this
answer
helpful?
Yes
No
+1
Monday, September 27th, 2021 AT 2:41 PM
Tiny
HAMFIST
  • MEMBER
  • 64 POSTS
So, here's the update: The customer contacted GM. They got a new fuse box assy. Still did not fix it. He shelled out a lot of money for the dealership to throw their hands up.

He then somehow found an automotive electrical whiz near him that chased down (from what I'm told) three bad grounds and things work great now.

So, that. Well, I'm happy I did not spend more time on it.
Was this
answer
helpful?
Yes
No
+1
Monday, November 8th, 2021 AT 1:19 PM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Faulty grounds strike again. One of these days I am going to figure out that this needs to be the first thing to check.

Thanks for coming back and updating us as I am sure that will help others in the future.
SPONSORED LINKS
Was this
answer
helpful?
Yes
No
Monday, November 8th, 2021 AT 5:28 PM
Tiny
HAMFIST
  • MEMBER
  • 64 POSTS
I just never know which one where to check.
Was this
answer
helpful?
Yes
No
Tuesday, November 9th, 2021 AT 8:32 AM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Agreed it is hard when you don't have codes to draw you to a specific system or module for to check those grounds. Thanks again. Talk to you next time.
Was this
answer
helpful?
Yes
No
Tuesday, November 9th, 2021 AT 2:47 PM

Please login or register to post a reply.

Related Fuse Panel Content

Fuse
GUIDE
Fuse
The design of a car fuse is to limit the amount of amperage being pulled through a particular circuit. When an electrical circuit has a problem such as a short to ground...

Sponsored links