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fuel pump and passlock

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Old 09-07-2010, 11:47 AM   #1
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fuel pump and passlock

I have a 1999 gmc sonoma. i replaced the fuel pump and now have problems. after installation the truck started and ran for nearly 10 minutes then shut down. i tried to restart and no fire. i still have pressure at the fuel line so i know the pump is still working. this morning i tried again and it started right up and then died with in 5 seconds. Does this sound like the passlock killing fuel at the injectors? how do i reset? how do i fix?

thanks for any help
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Old 09-07-2010, 08:51 PM   #2
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Re: fuel pump and passlock

I think the passlock keeps it from starting period.

find a good shop that installs alarms. often these guys know how to disable the passlock system so you can test it out. I've also seen a fair share of cars with bad keys that set off the passlock systems.

but first I think I'd check your pump connections and watch the pressure with a gauge. just because gas squirts out of the test port doesn't mean it's the proper amount of psi

Last edited by serpentracer; 09-07-2010 at 08:53 PM.
Old 09-08-2010, 10:54 PM   #3
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Re: fuel pump and passlock

Quote: Originally Posted by djwehr
I have a 1999 gmc sonoma. i replaced the fuel pump and now have problems. after installation the truck started and ran for nearly 10 minutes then shut down. i tried to restart and no fire. i still have pressure at the fuel line so i know the pump is still working. this morning i tried again and it started right up and then died with in 5 seconds. Does this sound like the passlock killing fuel at the injectors? how do i reset? how do i fix?

thanks for any help
If you suspect Passlock keep an eye on SECURITY light. If its on steady or flashing during crank then Passlock is not happy.

This system does not use special keys but does depend on a certain voltage being created and sent to BCM when the key is turned.

If SECURITY is lighted you could try password relearn ... see attached service manual extract.
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File Type: pdf 99 Sonoma - Passlock.pdf (27.2 KB, 327 views)
Old 09-09-2010, 12:57 PM   #4
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Re: fuel pump and passlock

starting to suspect back connection to pump, or problem with the pickup tube. when i installed the pump i filled the reservoir in side with fuel and the truck ran for 10-15 minutes. now nothing. i got to reading about the passlock and the light flashes when the door is open, and goes steady when key is inserted. but then goes out. gonna take a better look at the pump this weekend. will keep posted.
Old 09-09-2010, 01:37 PM   #5
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Re: fuel pump and passlock

I am having a similar problem with my 02, security light is on when door is open. However, i checked the fuel pressure and it was roughly 48psi funny part was when i hit the pressure relief button on gauge it barely bled any fuel through the drain tube. So, at this time i sprayed some fuel into the TB and she fired up for about 3-5 seconds, rechecked the pressure at shrader valve and fuel just dribbled out i will do a pump this weekend. I am more than sure at this point that is the issue but the insistant SES light has me bugged...
Old 09-09-2010, 03:51 PM   #6
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Re: fuel pump and passlock

Quote: Originally Posted by Gen210
I am having a similar problem with my 02, security light is on when door is open. However, i checked the fuel pressure and it was roughly 48psi funny part was when i hit the pressure relief button on gauge it barely bled any fuel through the drain tube. So, at this time i sprayed some fuel into the TB and she fired up for about 3-5 seconds, rechecked the pressure at shrader valve and fuel just dribbled out i will do a pump this weekend. I am more than sure at this point that is the issue but the insistant SES light has me bugged...
I just refreshed my memory on how the security system operates on my 2004 S10 crew-cab.

Its normal for SECURITY light to flash when door is open.

The light should light for a few seconds when ignition is turned on but should go off if the BCM recognized the ignition was turned by a key and not a screwdriver.

The SECURITY light will come on for 15 seconds or so when you lock vehicle doors. It'll then go off indicating the theft systems are armed.

Have you confirmed the fuel pump runs for a few seconds when the key is turned on? If not it could be the PCM not latching the fuel pump relay.

I'd be tempted to remove the relay and put a jumper between socket contacts normally connected to relay pins 30 and 87.

The pump will run unless the ECM B 20 amp fuse is bad - the fuel pump is bad - or there's a wiring issue between power and pump.
Old 12-03-2010, 07:58 PM   #7
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Re: fuel pump and passlock

ok, finally got to check some things. jumpered the 30 and 87 pin and got power to the rear wireing harness, but the pump will not run. with the relay in i do not get power to the rear. i tried my old pump that ran when i replaced it and no go either. I cant seem to find this ECM B 20 fuse. is there an emergency fuel shut off switch somewhere?
Old 12-04-2010, 07:45 PM   #8
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Re: fuel pump and passlock

Quote: Originally Posted by djwehr
ok, finally got to check some things. jumpered the 30 and 87 pin and got power to the rear wireing harness, but the pump will not run. with the relay in i do not get power to the rear. i tried my old pump that ran when i replaced it and no go either. I cant seem to find this ECM B 20 fuse. is there an emergency fuel shut off switch somewhere?
See attached schematic ... if you jumped 30 and 87 and had power to rear wiring harness (toward fuel pump) ECM B fuse must be OK (fuse is supposed to be on under-hood fuse block).

I'd think you need to access wires on tank - with test lamp - to see if you have power on gray wire. You'll need the jumper in to do this - or have assistant cycle the ignition switch when light is ready. The PCM only turns fuel pump on for 2 or 3 seconds each time key is turned on - unless key is turned far enough to crank engine.

If you have power on gray wire - and pump does not run - it could be connections to pump, the pump or bad ground (black) wire.

BTW ... the diagram does not indicate an emergency fuel shut-off switch is used. What's supposed to happen is any bump hard enough to deploy airbag will command ECM/PCM to remove power to fuel pump relay.
Attached Files
File Type: pdf 99 Sonoma - Fuel Pump Ckt.pdf (14.4 KB, 164 views)

Last edited by far2grumpy; 12-04-2010 at 07:46 PM.
Old 12-04-2010, 08:41 PM   #9
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Re: fuel pump and passlock

GM didnt use a cut off switch

instead GM uses the oil switch on the engine

if you dont have full 12 volts in the gray wire back at the tank then you got bad relay or bad FP wire along frame rail

do you have a full ground wire and a full 12 volts hot wire all times at the relay?

if not then you need to fix that

Last edited by fast68chevy; 12-04-2010 at 08:42 PM.
Old 12-04-2010, 10:23 PM   #10
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Re: fuel pump and passlock

fastr68,
I have 12 volts at the tank and ground when i jumper the relay, but the pump still wont run. i have replaced the relay with others and still no luck. how would i check for 12 volts at relay and ground?
Old 12-04-2010, 11:49 PM   #11
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Re: fuel pump and passlock

If you have 12v at the tank, either the PUMP or the PUMP ground, or the wiring INSIDE the tank is toast.

With the jumper in place wack the bottom of the tank to see if the pump starts.
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