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Hi Everyone. Having a bizarre problem with my 99 rx300
I'll post my problem in point form so its easy to read.
*My fuel meter went to empty and the warning light came suddenly (there was halfish tank at that time,just filled up)
*After about 3 weeks I took the left rear seat out and got to the fuel sender wiring harness.
*There was 4 wires. Fuel Pump positive and negative (thick wires) , then the fuel level wires (thin)
*I shorted two thin wires , so the fuel gauge should read a full tank. It didn't.
*I grounded one thin wire , nothing happened.
*Then I grounded the other thin wire then the fuel meter needle went to Full .So the meter works I guess?
*So the first wire I grounded should be a negative ground wire .So I tested the first wire for continuity with my multi meter . And it was not a ground ,that wire was not connected to the negative ground.I tested many times. I thought it was broken somewhere, so I cut the wire then connected it to a nearby bolt.
*The fuel needle showed a full tank ! yey I thought its fixed now (I had a full tank at that time.(not a good thing to do this with a full tank , but i didn't take the assembly out so....) )
*3 days later still shows a full tank with about 100miles driven. The needle hasn't moved a bit. Didn't sound right !
*I took the seat out again and removed the negative wire from the bolt.In theory this should make the fuel needle go to empty and the light should come on as before.But it didn't. Removed the whole harness , but the fuel needle didn't move a bit.
*Switched off and on the key many times , still fuel meter shows full with sending unit connecter removed ! what??
*Removed negative battery terminal for a few minutes. Connected it , then turned the key to ON, and now it shows empty with the warning light on ! This is bizarre !!
*Connected the ground bolt and the harness back , then the needle went to full.I didn't had full tank at that time.The reading is wrong.I put a 50 ohm resister in between the wire I grounded , the needle shows half a tank.So the gauge works right?
*Removed the harness 5 mins later , shows empty tank.I put the seat back and everything.
*The reading says full all the time?
So now i'm gonna get the whole assembly out and move the damn floater while connected and see for fuel needle movement, but the harness didn't get any ground on any of the thin wires when I first removed the thing.
Any advice?
(The wire I grounded to a bolt was the one that made the fuel needle NOT move when grounded.)
I usually DIY almost everything on this car and this one came very frustrating and time consuming of all.
Any help is welcome.
Please arm yourself with the wiring diagram. Without one you are shooting in the dark, Another good thing to have would be the service manual.
Since both have copyrights, we can not provide a local copy. Some folks have found some material on line, and once again we can not publish them here in Club Lexus.
I am not sure, but the fuel level info can come from the ecu and not directly from the float ... [there may not be enough damping if it is read directly and you will get moving display as you go over bumps]. Again I am guessing as I do not have the wiring information with me.
Please arm yourself with the wiring diagram. Without one you are shooting in the dark, Another good thing to have would be the service manual.
Since both have copyrights, we can not provide a local copy. Some folks have found some material on line, and once again we can not publish them here in Club Lexus.
I am not sure, but the fuel level info can come from the ecu and not directly from the float ... [there may not be enough damping if it is read directly and you will get moving display as you go over bumps]. Again I am guessing as I do not have the wiring informant of me.
Salim
What? There is a sub fuel gauge ! I had no idea , The one I Grounded is coming from this sub fuel floater. Where is it located ? I searched but all that comes up is guides and info about the main one.
I'm even more confused now.
mine was at 1/2 tank even after i filled at gas station, turn out that there are two fuel sending units, one is attached to the fuel pump under the driver side rear seat, with resistance 0 ohm for full and 40 ohm for empty, there is a main fuel sending unit under the passenger side rear seat, which was stuck at empty being too rusted, after i cleaned out the rust and now the floater can move freely, this main fuel sending unit has resistance of 0 at full and 70 ohm at empty.
09-21-18, 08:44 AM
99 RX300 Fuel Gauge Problem
