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Amedee, Toyota Technician
Category: Toyota
Satisfied Customers: 26623
Experience:  ASE certified tech advanced level specialist. Wisconsin certified emissions state inspector
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I have a 97 Geo Prizm (basically a Corolla) and I can not ...

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I have a 97 Geo Prizm (basically a Corolla) and I can not get the fuel pump to work. Ran tests according to the GM shop manual an it always leads to "Replace ECM" or "Run fuel pressure test" as the final result. I believe the ECU is fine, pump and relay are new. Wiring seems ok, resistance on grounds are all between 0.00 and 0.10 on ohm meter (20K setting). There isn''t a live wire to the pump which carries power to or from the pump assembly except for the signal from the float. Not sure where to go from here. Could I have purchased a bad relay or is my ECU shot?
Power is supplied to the fuel pump from the blue wire with black stripe.

This power comes from the relay. SOunds like the fuel pump relay is not getting the right inputs.

Here is a wiring diagram.

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Customer: replied 9 years ago.
I have power from GREEN/RED wire (ECU - 12V), I get power from BLACK/RED wire (12V), I have 0.06 ohms from WHITE/BLACK, nothing at all from BLUE/WHITE (which I assume is the output for the pump. But, I have no power form BLACK which I assume would be a ground. I tested it for a ground and got 5.62 ohms. I assume thats bad. So my next question: What is the "Opening Circuit Relay CELL 20" on the diagram and where does it go / what does it do? How do I fix it?

Thank you!
I will have to pull another diagram for you.

I assume it should be power. You could try powering that wire up and see if that helps.

The blue/with black stripe wire is the output to the pump.

You should be getting a ground on the green with red wire from the computer. The computer controls this relay by grounding it.
Customer: replied 9 years ago.
Ok, I might have my info mixed up on the wires. I cannot remember for sure on the green/red wire but I wrote down 12V. I'll check that tonight. I do remember distinctly that I did not receive any voltage at all from the BLACK wire and since I am unclear on what it does I assumed it was a ground. According to the manual there should be a starter signal to the same relay. Maybe thats it? Either way the pump should fire upon turning the car to the "ON" position which it does not do. So I should power the black wire and if it runs, then what do I do if it does? What do I do if it doesn't?
If it runs, than we know everything else is working properly. If it does not run, chances are something else is not right in the circuit.

THe reason I think it should be power, is that every relay should have at least 2 powers going into it. ALso, if you look close at the wiring diagram, with it right side up, all the powers are on top and all the grounds are on the bottom. The black wire goes into the top of the relay indicating that should have power.
Customer: replied 9 years ago.
Ok, makes sense. Last question then I'll leave you alone, ha ha. Where does the BLACK wire go? I mean I can't find anything on the "Opening Circuit Relay CELL 20" in the manual. I have no idea where to go from there besides tearing apart the wire loom and following it. Do you think it goes to the firewall?
Look towards the top of the diagram. The black wire.


Customer: replied 9 years ago.
(I know I said one more, just to confirm) Ok, so technically no power to BLACK during cranking means either a bad wore or relay. If it cranks, then most likely that black wire is broken somewhere? Sound legit?

Your close!

If there is no power to that black wire while cranking, you could have a bad neutral safety switch (auto trans) or a bad clutch pedal switch (manual trans). FOllow the black wire on the diagram. It comes from the ignition switch and then goes through the safety switch then to the relay. YES! it should have power. If not, you have a break in the wire and or a bad switch.
Customer: replied 9 years ago.
And if there IS power to the wire while cranking? I checked that at the beginning and I am pretty sure the BLACK wire had power during cranking. Bad open circuit relay for the fuel pump? Could it be possible I might have gotten the wrong relay. Same size, shape but color and numbers are different then stock part. It came from an auto parts place, they said it was the one I needed. (I know I am a pain but I have been working on this car for a month now and I need to cover my bases)
THats ok

If there is power on this wire at the fuel pump relay and the relay is still not activating, chances are that there is another problem. I would be wiling to bet that the relay is ok.

If this is the case, I would check all the other inputs to the relay. Look closely at the one that comes from the pcm. This one should be grounded. You can always ground this wire from the pcm and see if that activates the relay.
Customer: replied 9 years ago.
Ok, I think that is the only thing left I have to try. Thank you very much for your time!
Customer: replied 9 years ago.
No input from ECU. I grounded the wire (from the relay to the pump) to the chasis and it worked. Car still would not start. There is spark, pump seems to be flowing the correct way, and the pump runs the entire time the car is cranking. The car will not start. The pump quits when you pull the jumper (to the chasis) off. Should I shop for an ECU?

Before you do that, we must check all inputs to the computer. I think you will be missing either a ground or a power.

THere should be at least two powers and two grounds. You are going to want to check for these with the key on.