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Old 09-17-2023, 04:08 PM #1
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Making a cor (circuit-opening relay) test relay

I've learned alot from here with many thanks, want to contribute. I haven't found a summary of the interesting COR, so here goes. Additions & corrections most welcome.

The purpose of this relay is to cut off fuel supply in case of accident or other. Even if the ignition is on, there will be no fuel pumping action when the engine is not running. The ECU senses engine non-op and will not ground its FC terminal, thus preventing the pump ground circuit from completing. The ECU allows the pump to run during cranking and when the engine is running. This test relay allows fuel pump to run with ignition in the 'On' position and engine not running.

RockAuto and others have the 3rd Gen Circuit Opening Relay (COR); it's a 'Standard RY302' relay for ~$7.00 (see pic), they have several different brands. With 3rd Gen, the factory obsoleted the expensive old dual-coil COR, nice.

Pry your new test relay cover off carefully with a couple of thin-bladed screwdrivers. Cut the corner off of an old credit card, or some piece of plastic that wedges the new normally-open (NO) 30-87 relay contacts firmly closed without bending anything (see pic).

After mod & before installing, use VOM to test relay for new function (as now modified) and NO SHORTS (other than the 30-87 pins short you just created). This mod allows ECU to continue seeing correct FC circuit resistance (the relay coil), a good thing.

The COR is located behind the lower finish panel by driver's left knee (see pic) in my 1997 T4R. Finish panel uses 4 x 10mm screws and comes off easily.

I included a picture of my factory OEM COR.

Benefits:
1) Have spare COR if needed (just pull out CC corner). This is a common relay on 3G T4Rs, so spare for those too.
2) Have fun watching your truck kick right off when cold. Though my truck kicks off with about the same delay as when a factory COR is fitted, so who knows...
3) Use for troubleshooting fuel pump, ECU, & local wiring.
4) Test fuel pressure more easily. Pump remains running with ignition in ON position. BE SAFE. I can hear the pump running with modified relay, it's a threshold-of-hearing high-pitched whine one can hear if you tilt your head and hold your tonque just so...

CAUTION: this is ONLY a testing relay. If you use it to keep your truck running, then FIND THE PROBLEM so you retain the fuel safety of a factory COR circuit for your truck.

Perhaps there is a jumping of the DLC1 port that could achieve the same thing. Or the factory DLC3 Toyota Hand-Tester--are those even available...?
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Making a cor (circuit-opening relay) test relay-cor-relay-location-jpg  Making a cor (circuit-opening relay) test relay-generic-replacement-cor-relay-jpg  Making a cor (circuit-opening relay) test relay-cor-test-relay-cc-wedge-jpg  Making a cor (circuit-opening relay) test relay-oem-3g-t4r-cor-jpg 
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Old 09-18-2023, 03:09 PM #2
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Did Toyota stop putting the Fc pin in the diagnostic connector in the engine bay? All you (used to?) need to do is put a jumper between the B+ and Fc connection there to test full-time fuel-pump operation with key-on.

They may have eliminated that with the transition to OBD-II though, even if the pin is marked, it may not be populated in the connector.

-Charlie
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Old 09-18-2023, 10:51 PM #3
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I'll see if I can get a decent photo of my DLC1, it's pretty tall and narrow.
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Old 09-19-2023, 03:04 PM #4
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1997 T4R DLC1 Terminals

I had a good look at my DLC1 (engine bay) and there is no Fc terminal shown in the cover diagram (see pic). The closest is an Fp terminal. My factory WSM mentions in several places that the way to power the fuel pump is by direct jumping to the terminals on the pump itself. Not very elegant, c'est la vie.


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Originally Posted by phattyduck View Post
Did Toyota stop putting the Fc pin in the diagnostic connector in the engine bay? All you (used to?) need to do is put a jumper between the B+ and Fc connection there to test full-time fuel-pump operation with key-on.

They may have eliminated that with the transition to OBD-II though, even if the pin is marked, it may not be populated in the connector.

-Charlie
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Making a cor (circuit-opening relay) test relay-dlc1-cover-diagram-jpg 
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Old 09-19-2023, 04:59 PM #5
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Originally Posted by LateRunner View Post
I had a good look at my DLC1 (engine bay) and there is no Fc terminal shown in the cover diagram (see pic). The closest is an Fp terminal. My factory WSM mentions in several places that the way to power the fuel pump is by direct jumping to the terminals on the pump itself. Not very elegant, c'est la vie.
Ack, you got me. Fp is the correct location. Open up the cap and see if a pin is there. It isn't shown in the diagrams, so it may not exist. It is there in the (same shaped) DLC connector on my older (pre-OBD-II) Toyotas. Some cool stuff used to be in there - Oxygen sensor signals, the location to read check engine lights, the Vf pin(s) are used to read fuel trims, etc. - again, this is all pre-OBD-II...

-Charlie
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Old 09-19-2023, 05:56 PM #6
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Yeh, I been reading about the pre-OBD2 cool stuff for DLC1. I don't have a terminal in the Fp slot on my DLC1. The only thing I've come across so far in my 1997 T4R WSM is jumping pins E1 & TE1 (both of which I have) for checking the ignition timing. One doesn't pull out the 'Short Pin' for that one.

I might start another thread about 'Uses for the Post-OBD2 DLC1 Port', but maybe that's too wonky...?
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