100 series Sub tank fuel Gauge playing up

Submitted: Monday, Jun 29, 2009 at 23:22
ThreadID: 70253 Views:10978 Replies:4 FollowUps:2
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Has anyone got a wiring diag of knowledge of the 100series (HZJ105R) Aux/ sub tank sender wiring.

Main tank gauge readout perfect
Sub tank varies every time you push the fuel changeover switch, though more and more often sits on empty
(yes I have filled it)

Have replaced Sub tank sender and it worked for a few days.

How is the signal swapping for the gauge wired,.
Through the switch, or does the switch only switch the fuel line solenoid valves and the fuel gauge signal is changed through the solenoidsd as well.

Is there a common fractured wire/ bad plug problem in the harness

Really starting to annoy me. all ready spent a lot of time changing the tank sender unit. so before I start pulling everything apart I thought I would ask all the experts out there, that may have had the same problem


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Reply By: Flywest - Tuesday, Jun 30, 2009 at 01:08

Tuesday, Jun 30, 2009 at 01:08
I claim to know nuttin bout 100 series cruisers.

That said - I've replaced tank sender units in my boats fuel tanks before today.

Best I know they work like this - but I'm happy for anyone who knows better than me to stand corrected.

Theres some kind of a float made of plastic that obviously "floats" in the fuel.

In my experience it was a float that had a magnet embedded in it and the plastic float was shaped like a doghnut - i.e. with a hole in it.

This round plastic float with the hole in it could travel up and down a stainless metal tube, that seemed to have some kinda resistance wound coil of wire inside of it. The two wires out of the resistance coil went to the dash gauge.

It appeared to me that - as the float went up and down the stainless shaft, the magnet caused some kinda metal slide inside the shaft and wound coil to travel up and down along with it by magnetic attraction.

As the metal inside the coil contacted the copper wound coil at different heights it altered the resistance in the coil.

The gauge appeared to "measure the varying resistance" and depict it as either a full or empty or part full fuel tank depending wherre the float was and hence the metal inside the coil in the stainless tube and thus how LONG the crucuit was in the resistance coil.

I know about 5/8ths of naf all about electrickery so take this with a grain of salt - but when I had the sender out I connected a voltmeter thingy across the connections and as the slide went up and down the voltage or amperage or something on the meter went up and down.

For me, putting a new sender in worked a treat!

For you it would appear that, a shorting wire anywhere between sender and gaugue would register as varying amounts of zero resistance upwards, depending how bad the short and how worn the wire insulation..

That would be my guess - I swapped my 80 series cruisers sender for the sub tank into an auxilliary tank we installd and it appeared to work on a similar principle - with a float and two rods that pivoted up or down with the fuel level and went thru some kinda resistor.

Best I can guess - yours probably works in a similar way, maybe you need to be using a multi meter to test your resistance readings along the wire from sender to gauge, to find your short (or just run another wire and be done with it) - it COULD (most likely) be as simple as a bad EARTH connection on the negative wire, either right near the sender, or at the gauge dash install.

Then again - I could be spruikin outta my hat.(Seems like a few here reckon I don't know squat bout nuthin!)

Best of luck with it - I tell ya electrcikery de the work of de debil.

AnswerID: 372400

Reply By: Mr Pointyhead - Tuesday, Jun 30, 2009 at 08:14

Tuesday, Jun 30, 2009 at 08:14
There was a toyota recall on problems with the subtank gauge.

AnswerID: 372408

Reply By: cruza25 - Tuesday, Jun 30, 2009 at 10:58

Tuesday, Jun 30, 2009 at 10:58
hi Harrow

i have exactly the same in my 99 model
i removed the sender and it all tested ok, i removed and tested the switch- all ok

i presume it is a wire or connection or relay somwhere but as yet unable to find detailed wiring layout

i think its just a matter of getting underneath and tracing the cable from the sender under the vehicle and checking wires and connectors- maybe a broken wire or mud in a connection block.

mine was intermittent at first then got worse - now it just drops right to empty all the time and the light flashes on the dash.

we can wait and see if anyone else has a fix. i asked on lcool but without success



AnswerID: 372440

Follow Up By: Member - Graham H (QLD) - Tuesday, Jun 30, 2009 at 13:35

Tuesday, Jun 30, 2009 at 13:35
From my Haynes manual
The colours are V/GR V/W V/R
V being violet

All the way back to the gauge.

My boss had trouble with his 2003 Sahara sub tank and they had to replace the whole unit as there was a fault with some About $1500 worth I think.
However his wasnt pumping either.

FollowupID: 639684

Reply By:- Tuesday, Jun 30, 2009 at 13:29

Tuesday, Jun 30, 2009 at 13:29
I had a problem with my sub fuel tank guage and so did a friend of mine. Seems to be a common problem.

AnswerID: 372459

Follow Up By: Member - Graham H (QLD) - Tuesday, Jun 30, 2009 at 13:40

Tuesday, Jun 30, 2009 at 13:40
Forgot to say I have read of electrical resistance problems in the instrument cluster on some 100ser.
Apparently they were replaced by toyota.

FollowupID: 639685

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