2002 GMC Sonoma voltage testing at the fuel pump

SCOTT732

MEMBER
2002 GMC SONOMA
6 CYL
4WD
AUTOMATIC
126,000 MILES

How do you check for faulty fuel pump. Can't hear the pump run when the key is turned on. What should voltage readings be at the fuel pump.I have the 5 volts when the key is turned on, but can you check for 12 volts if the truck doesn't run? If so which wire should it be?

Thanks
Scott

4 Replies

RASMATAZ

MECHANIC
75,992 POSTS

Direct power to the fuel pump from the battery the Gray wire is the power circuit and black is the ground on the fuel pump connector and see what happens.

Do a voltage drop

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Sunday, March 30th, 2008 AT 6:00 PM

SCOTT732

MEMBER
3 POSTS

I pulled pump. Applied 12 volts. The pump didn't run. Picked up new one. Tried tested it before I put it in. Worked fine. Dosent work in the truck. Applied 12 volts to grey wire and it worked. Took voltage reading at harnes. With key on. Got 3 to 5 volts for a few seconds. Then tried cranking it over. Got the same voltage reading only it was constant. Checked all the fuses under the hood and in the cab. All good. Switched relay with another of the same number. Made no differents.

Any ideas would be greatly appreciated.
Thanks
Scott

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Monday, March 31st, 2008 AT 2:37 PM

RASMATAZ

MECHANIC
75,992 POSTS

Check the ECM B fuse and also trun key to On check for power at A8/B8 orange wire should have battery voltage no voltage the problem is coming from the computer. Also check ground on relay connector F7 to chassis ground-

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Monday, March 31st, 2008 AT 6:40 PM

SCOTT732

MEMBER
3 POSTS

Rasmataz, I'd like to thank you for your help. It was very usefull. The problem turns out to be in the ground circuit. I plan on tracking it down this weekend.
Thanks again for all your help

Scott

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Thursday, April 3rd, 2008 AT 6:36 PM