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Dave Nova
Dave Nova, ASE Certified Tech
Category: Toyota
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Experience:  ASE Master Certified. 25 yrs experience
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Toyota Tundra SR5 I am totally stumped on a Fuel Pump/relay/

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I am totally stumped on a Fuel Pump/relay/??? problem. This is on my 2000 Tundra (200k +), 4.7l, V8.   The problem is, that it (the Fuel Pump relay slot) is not getting any power to it with the key on (with the relay itself being the only missing part). The fuel pump seemed to be the culprit, so this is where I started. I still have the stock fuel pump, so I listened to the tank through the open cap, no noise. I then pulled the fuel filter and turned the key to on and even cranked for a second, no fuel coming out the tank (there is 3+ gallons of fuel in the tank). I checked the fuses (IGN, EFI), I rotated the Circuit Open relay and EFI relay (both relays caused a click when inserted into the EFI relay slot (key on)). I pulled the fuel pump and it works with or without gas (bench test) and both the EFI and Circuit Open relay slots (with relays removed) get power when key turned on. The fuel level gauge works (if that matters), it is getting power anyway. I am not sure where do go next, CMP sensor, CKP sensor or the main brain (PCM). Although they should be working if the open circuit relay socket (slot) is hot when key on.  <br /><br />Thanks for any advise or help...
Hello and thank you for using JustAnswer. My name is XXXXX XXXXX I will do my best to assist you with your Toyota problem.

The fuel pump relay should have power on 2 terminals. The fuel pump relay is powered through the EFI 1 fuse, the EFI relay and the C/OPN relay. Check this fuse first, then try swapping out each of these other two relays to see if you get power to the fuel pump relay.

Customer: replied 5 years ago.
With the ignition in the on position and a good charge...

I have checked the EF1 fuse and I am getting power to EFI relay socket and C/OPN relay socket. Furthermore, I get power to two terminals on the EFI socket when (the 3 (Fuel Pump, EFI & C/OPN relays) are removed (like I should) and only one hot terminal on the C/OPN socket (like I should). However, there is no hot terminals in the Fuel Pump socket (like I should).

When I plug the EFI relay back in, I hear a click and something else, but I do then get two hot terminals in the C/OPN socket (like I should). Again, no power in the Fuel Pump relay socket (as it should be). I then plug the C/OPN relay in and get no power (0 terminals) in the Fuel Pump relay socket (which there should be 2 hot terminals).

Looking at the your and mine (schematics), I have to think it would be actual loose wires or ??? It appears one wire (from the C/OPN relay, when charged) powers the Fuel pump relay at 2 terminals, which makes me think it has to be the C/OPN relay but it can be swapped and I get the same results (with getting 2 hot terminals to C/OPN relay socket) with either relay. Back to wire/connection, the fuel pump resistor is after the fact?


Can you see the wiring going to each of the relay sockets to identify the wire colors?
Customer: replied 5 years ago.
No, they are buried in a 4" x 10" plastic box. Everything is so tight, I can't check power exiting C/OPN relay without dismanteling something.

I was afraid of that. I believe the problem is going to be on the Black/White wire coming out of the C/OPN relay over to the FUEL PUMP relay. Next step is going to be removing the fuse/relay panel to get to the back side to check this wiring.
Customer: replied 5 years ago.
I pulled the guts from the fuse box and determined the black/white wire path has no resistance between the C/OPN terminal and 2 of the Fuel Pump socket terminals. Could have done this without remmoving the guts, but was able to visualize the path and confirm a complete circuit.

Back to the relay (C/OPN and EFI), it almost has to be?

I will pick up one and a new fuel filter, while I'm there.

Any other ideas?

I will accept...

With the key on and the EFI relay energized, pull the C/OPN relay out and reinstall it. Does the relay click as it is installed?
If the C/OPN relay is not clicking on, then check the 5 amp IGN fuse to make sure it is good. The relay also then needs a ground from the ECM to energize. This ground is on the Yellow wire at the C/OPN relay.

Customer: replied 5 years ago.
I had to run to town and wire the battery back in. Then got hit with darkness and cold.

The C/OPN relay does not click when reinstalled (tried brand new relays (EFI and C/OPN)). I also switched the IGN (5 amp) fuse, with the turn signal 5 amp fuse (turn signal works before and after).

With all the relays back in and everything connected (fuel pump connected outside of tank). I get power at the wires behind 3 of the 4 of the C/OPN relay socket. The black and white wire that leads to (two terminals) on the Fuel Pump relay socket (from the C/OPN socket) has no power. All 5 terminals of the Fuel Pump relay socket are dead (again this is with all relays installed (EFI and C/OPN relays being new).

The power will not pass beyond the C/OPN relay socket. Could this have something to do with the Fuel Pump resistor?

This would have nothing to do with the fuel pump resistor, the resistor will be after the fuel pump relay. If there is a yellow wire on the backside of the C/OPN relay, try providing a ground to this wire and see if the C/OPN relay will energize and supply power to the fuel pump relay.
Customer: replied 5 years ago.
There is a yellow wire coming from the C/OPN relay socket, that is putting 12 volts out with the C/OPN relay installed.

You want me to ground the yellow (hot) wire?

Just want to make sure...
Yes, the power is coming through the relay coil. Grounding the wire should energize the relay and pass power on to the fuel pump relay.
Customer: replied 5 years ago.
I did ground the yellow and the little fellow (Fuel Pump) started to spin.

Tell me it is not the ECM... please.

Thanks for all of your patience and help.
You can check the wire for continuity back to the ECM before condemning the ECM.
Since the C/OPN relay does not get power until the key is on, you could just ground the yellow wire permanently to bypass the input from the ECM.
Customer: replied 5 years ago.
That is what I was going to ask. Will that have any effect with delivery of fuel? Does the PCM control flow through the yellow wire based off driving conditions. I don't think so, but had to ask.

We had snow and I was out of town, most of yesterday.

I tried the continuity check on the yellow wire and nothing. Just in case I hit every yellow wire, didn't have a good schematic to show the connections at the PCM (ECM).

Thanks again...
The fuel pump is constant duty, it does not turn off while the engine is running. Grounding the yellow wire permanently will not cause any driveability problems.
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