FUEL TANK warning light in dash & sub-tank won't transfer. Help Needed! (1 Viewer)

[1303]

The day after I finished upgrading my stereo, the FUEL TANK (orange color) warning light came up in my dash. Fuel was low in the main tank and when I tried to press the sub-tank transfer button in an attempt to pump the fuel from the sub-tank to the main tank, the green light on the button lighted up for a second and went out. Obviously, the transfer did not take place.

I went to fill up the main tank yesterday. I put about 50 Lts to an almost empty tank. I drove off with the FUEL TANK warning light still on. However, after about 1 minute or 2, the warning light went away and I thought it was likely the float was stuck because of the low level on fuel at the time and now it sort of fixed itself by freeing the float due to the filling of fuel. Apparently, that was not a correct assumption.

After I had driven for a couple of hundreds kilometers, I tried pressing the sub-tank transfer button again to confirm if the sub-tank transfer system was fixed. The same thing happened. The light on the button came up for about a second and then went out. No fuel was transferred. It was noted that the warning light was not on at this time.

I drive the rig further to a point that the fuel was low again. The FUEL TANK warning light came back on again.

What could be wrong with this? Please point me to a direction where I could start to check which parts are at fault.

Thanks for your help.

 

[CycloSteve]

IMHO the fuel tank "low" light is working fine. Fuel is low, and it is coming on at that point. The float assembly itself does not give the signal of low fuel. It is a separate sensor in the tank. Still, I think you are OK with that issue.

Are you sure you have any fuel in the Sub? The system will not transfer any fuel from the Sub to the Main under two conditions...Sub empty = system off, Main over 75% full, system off. There are separate Fuel Level Switches in both the Main and Sub tanks which switch the system off in this situation. The Subtank sensor is pretty simple to access, but the main is a PITA, as you have to at least drop it partially.

This is the diagnostic sequence. I figured out that my sensors were dirty, and fixed them. Hopefully this helps.



Steve

P.S. I hold my Subtank switch for about one second to get the system to engage. Otherwise it does not start the transfer process.

 

[1303]

Steve, the FUEL TANK warning light is not the same as the 'low' fuel warning light. As I understand, the FUEL TANK warning light comes on if there is a problem with the fuel transfer system.

 

[FISHYINK]

in my 80 i disconected the battery, to replace it, put the new battery in and the sub fuel light came on in the dash, (i have no sub fuel tank), so i disconected the battery and pluged it back in again, the sub fuel tank light turned off on the dash. and has stayed off ever since.

 

[CycloSteve]

Wild guess...you have a diesel and the light is the water separator light, indicating that you need to clean the filter / sedimenter? US 80's do not have this light operational as we do not have diesels.

Third light from the left.

If so, these threads should help.

https://forum.ih8mud.com/80-series-tech/322681-what-heck-indicatior-light-mean.html

https://forum.ih8mud.com/80-series-tech/185534-question-non-usa-owners-oem-subtanks.html




Steve

 

[1303]

It is not a deisel but a 1fz-fe FZJ80. I will take a picture to show you later.

On the other hand, which FSM did you refer to with the auxillary tank info in your previous post? Please advise.

 

[CycloSteve]

Non-US FSM pages from the ElMariachi OEM subtank installation thread. A picture would definitely help, as others may be able to figure out what is triggering the light, and what it could potentially mean.



Steve

 

[rove_mcanus]

The fuel tank light does mean there is a problem with the fuel transfer system. It is a warning light a bit like the check engine light. A computer logs an error code, and you go through a procedure to fix it.

It's hard to read, but the terminals to short are Tc and En

 

[1303]

That is an useful piece of information.

Does anyone have any pictures showing how and where to locate these fuel level switches. BTW, I checked in toyodiy.com and found there are a few of these switches in the engine bay. Are they in any way connected. They are also termed switch, transfer indicator #1, #2, #3 & #4. I think the parts diagram at least shows 3 of such in the engine bay. Someone correct me if I am wrong.

 

[rove_mcanus]

Following a PM, it would seem at least two people (me and the person who messaged me) don't have an En pin in the check connector.

On page BE-56 of the 1992 chassis suppliment manual, for those playing at home there is the procedure for checking the Sub fuel tank ECU. One condition involves shorting Tc and E1, so perhaps this is the correct combination for reading the codes.

Also in case it wasn't clear, it's the light on the sub fuel switch that is meant to blink the codes, not the FUEL TANK light in the dash. (unless the manual is also wrong there )

I'll also add that there is a list of the most common causes of sub tank failure (in order of likeliness). It reads:

1. ECU-IG fuse, or ECU-B fuse
2. Fuel pump
3. Sub fuel switch
4. Fuel solenoid valve
5. Fuel level switch (main and sub tank)
6. Sender gauge
7. Fuel Pump Control ECU
8. Wire Harness

 

[rove_mcanus]

That is an useful piece of information.

Does anyone have any pictures showing how and where to locate these fuel level switches. BTW, I checked in toyodiy.com and found there are a few of these switches in the engine bay. Are they in any way connected. They are also termed switch, transfer indicator #1, #2, #3 & #4. I think the parts diagram at least shows 3 of such in the engine bay. Someone correct me if I am wrong.

The switches it refers to are in the tanks. The main tank has a seperate switch (that also works the low fuel light), the sub tank is a combined unit.

 

[CycloSteve]

The main tank switch is the bottom one on the main. Unfortunately no access panel to reach it, but you can test the plug from the access panel under the second row of seats.

The sub tank switch is accessed via the panel under the 3rd row of seats. Much easier to get to from within the truck.

Steve

 

[1303]

I removed the 2nd row seats and took out the lid that hides the opening of the fuel gauge sender and the wiring.

I followed the instructions and disconnected the level switch connectors to measure the continuities of the 3/4 switch and the 1/4 switch (the continuities of terminal 1 & 2 to 3). At the time, I was almost empty on the main tank and had about 50 lts in the sub-tank. I obtained an 'on' for the 3/4 switch (which is correct) and an 'off' for the 1/4 switch (which is not correct). I thought I found where the fault lies -- the 1/4 switch got stuck and was giving an 'off' signal that is not agreeable with the 'less than 1/4' signal that the fuel gauge pciked up from the sender, hence the FUEL TANK warning light was lit and fuel transfer from sub to main cased to work (botton pressed with green light on for 1 second and then went off).

To re-confirm my finding, I deliberately shorted the 1,2 & 3 terminal (these are also meaasured to be connected to Ground) on the cable side (as opposed to the level switch side), trying to fool the ECU that the 1/4 signal was also 'on'. I reset the ECU to get rid of the FUEL TANK warning light. When I started the rig, all went well. I psuhed the Fuel Transfer button and the light came on and started the fuel transfer from sub to main. This went on for about 10 seconds, and the FUEL TANK warning light came back and the green light on the Fuel Transfer button went out, transfer was then stopped.

Any ideas what is going on here? I tested the solenoid valve and the sub-tank fuel pump and both are working fine, I beleive. Am I missing something here?

 

[CycloSteve]

Technically you can test the Main tank switch by unplugging it and bridging terminal 1 to terminal 3, and terminal 2 to terminal 3 on the body-side of the harness. This would "fool" the ECU to think that the float is in the down position, thus OK to pump (just provides a ground signal to the ECU). If the system passes this test, you maintank switch should be pulled and cleaned. If cleaning does not work, replace. As I said earlier, it is not fun to drop the tank, but may be necessary. Be sure to drain it as much as possible, as it is effing-heavy even empty.

The rear one can be tested also in-situ by unplugging the plug. This open circuit makes the system think that the tank has fuel. Removal and cleaning is a quick and easy job via the access panel.

Both of these are just tests, but should help point you in the right direction. Other issues could be that your under-rig connectors are dirty and need cleaning plus some dielectric grease added...others have had that problem. Check the plug at the ECU in the rear panel too while you are at it.



Steve

 

[1303]

Technically you can test the Main tank switch by unplugging it and bridging terminal 1 to terminal 3, and terminal 2 to terminal 3 on the body-side of the harness. This would "fool" the ECU to think that the float is in the down position, thus OK to pump (just provides a ground signal to the ECU). If the system passes this test, you maintank switch should be pulled and cleaned. If cleaning does not work, replace. As I said earlier, it is not fun to drop the tank, but may be necessary. Be sure to drain it as much as possible, as it is effing-heavy even empty.

I think I did exactly that by bridging terminal 1 to terminal 3, and terminal 2 to terminal 3, but this did not get rid of the 'FUEL TANK' warning light and no transfer could take place.

On the switch side, as I said, with the main almost empty and sub almost full, I checked the connector terminals (on the siwtch side) and obtained the 3/4 'on' and the 1/4 'off'. This had me puzzled.

I will turn to testing the connector terminal at the sub today nd hopefully I will be able to get more clues.

 

[1303]

Today, I disconnected the switch connector again and plug another new one in. Pressed the transfer button and the green came on and remain on...the fuel transfer function resumed as it should be.

I then dropped the main tank in an attempt to see if the fault would go away via cleaning the switch itself.

This is as as far as I have gone for today. Tomorrow I am going to take the switch out for cleaning. Hopefully, this would cure the problem. If not, I would need to replace it with a new one.

I still could not figure out as to why I could not fool the ECU to 'think' that the maintank is empty by bridging terminal 1 to 3 and 2 to 3 at the cable side. Anyone got any ideas?

 

[CycloSteve]

I would definitely check all of the connectors to be sure they are clean inside.

The one for the main tank also has a connector just under the B pillar around/above the frame IIRC.

The subtank connects at the tank access panel, then again at the rear crossmember...both should be accessable without removing that tank.

The ECU could also have some corrosion, as the rear quarter panels often have leaks from the belt moulding under the windows...pull the whole interior panel to reach the ECU.

The pump assembly also has a series of plugs under the truck!

If you have access to all of the plugs at the tank-sides, and the ECU unplugged, you can also Ohm them out to be sure that they have connectivity from and to the right pins at the ECU.

Here are a few diagrams which S.CarolinaFZJ80 posted which may help.



Steve

 

[1303]

Removed the main tank level switch today. Opened the 1/4 side float switch mechanism and cleaned it. Both the 3/4 and 1/4 showed continuity terminal 3. Plugged it right back, the transfer function came back to life again. For reliability sake, switched the new one in and kept the old one for spare.

Thanks for everyone's help, especially Steve and rove_mcanus. Good stuff.

 

[1303]

A follow up on this:

Ever since, ecerything ran fine except that the 'auto' transfer function of fuel from the sub tank to the main has been lost (the transfer used to be sort of automatic when the main tank fuel level drops to a certian low level before all these happned). Now, the transfer can only be initiated by manually pressing the transfer switch button. Any ideas? Could this be a feature of the old level switch I swapped out?

 

[CycloSteve]

With my rig it is 100% user-initiated with a push of the dash transfer switch, so not of much help here.



Steve