Bypass the fuel pump relay



Tardis suggested that I could empty my gas tank by:

“Bypass the fuel pump relay and just let the fuel pump pump all of the gas out.”

How do you do that on a 2002 Prism?


Talk is cheap on this board…

Get a 6’ length of 1/4" clear plastic tubing and work it down into the tank and siphon it out…


First you need to locate the fuel pump relay. When you do, remove it. Bend out a paper clip, and connect it between the power terminal of the fuel pump socket and the fuel pump terminal. It make take you a little experimentation to find the correct two terminals, but you don’t have anything to lose anyway.


Well, you would know. You seem to post about a lot of cars that you have never had or worked on.
Right after Katrina, I used the fuel pump trick that I am suggesting to pump the gas out of several of my neighbors flooded cars. We used the recovered gasoline in our generators. Gas was like gold here for a few days, and the newer cars had gas tanks that were sealed enough that little to no water got in.
Yes, I have also fished a small plastic tube past the rollover valve, but I found that the fuel pump trick was much faster.


I believe you could just apply 12 volts to the test/prime connecter under the hood.


I for one liked your idea. I’m tired of the taste of gas. I keep trying to remember to pick up a decent handheld siphon pump at the parts store for my seasonal drainng of my lawnmower and snowblower.


Probably not. I used to occasionally siphon gas for the lawnmower. Hasn’t worked on any of our cars for twenty-twenty five years. After the gas shortages in the 1970s “they” put baffles in the fillpipe/gas tank intended to block siphoning hoses. The baffles work, at least when I’m the guy trying to siphon the gas.

I think that the Prism is a rebadged Toyota Corolla. If so, there is probably an access panel under the back seat that will allow access to the fuel pump, a fuel pump wiring connector, a gas hose connector, and – if all else fails – the interior of the fuel tank after the fuel pump is removed. (not recommended as pulling and reinserting the fuel pump probably involves dealing with itsy bitsy screws in awkward to get to places.)


That seems a little harsh, man.


For years, Chevrolet has put a test/prime connector near the fuel pump relay; but, the Prism isn’t a Chevrolet design, is it? So, to hot-wire the fuel pump, you’ll need to pull the Circuit Opening Relay in Junction Block #1, and apply + 12 volts to terminal #1 to the blue/black wire which powers the fuel pump.


Would this work?

I’ll assume that the pump’s output has been diverted from the injection fuel rail (piece of tubing run into a gas can), because you have to to that no matter what.

I THINK that when you switch on the ignition the pump runs until the system is pressured up. (You experts often ask “car won’t start” posters if they hear the fuel pump run when they switch on the ignition.) So, if the fuel is not getting to the system (it’s going into the gas can), and no pressure builds up, would the pump keep running? Or is there a back-up time limit on that initial operation of the pump?

Just trying to learn.


No, there is a safety time-out. The pump will only run for a few seconds. Most systems (not all) don’t even measure the pressure, so they don’t know if it pressurized or not.


I also used the ‘Jumper the fuel pump relay’ trick after my niece was in an accident that punctured the fuel tank. I didn’t have time to pull the tank, so I used the jumper method to drain the tank, putting the gas into gas cans, then got a chance to do the tank 2 weeks later. With the other repairs we had to do to the car, this was the quickest way to go. This was on an '86 Buick Lesabre.


Thanks. It does make a lot of safety sense to do it that way.


I found that I could snake the tubing into the tank through a linear approach after I removed the filler pipe at the flexible coupler (it had a tubing clamp that I was able to loosen). It was then easy to siphon most of the gas out of the tank.

Thanks for all of your help. Your tips let me save the gas!