How to repair Fuel light and Travel Navigator/computer

[sportsfreaked]

The problem arose where my fuel light would not come on when it was suppose to (low on fuel) and on my travel navigator/computer I had the flashing dashes under QTY and RANGE. The fix is a $0.66 THC Thermistor part on the fuel sending unit. This is how to fix that issue.

I ordered my via Newark.com. The part number for the THC Thermistor from Newark is 20F735. The actual manufacture of the Thermistor is AMPHENOL ADVANCED SENSORS and their manufacturing part # RL2004-582-97-D. I ordered 4 of the thermistors from Newark and with USPS shipping it was $8.00. You will need a soldering iron and a solder removal tool as well.

First thing is to remove the seat and then remove the fuel sending unit from the tank. When you remove the sending unit you will see a small canister towards the bottom that has a yellow wire connected to it.

It's best to leave the canister connected to the rod. If you look at the bottom of the canister you will see a blob (technical term) of solder. This is where one lead is soldered to the canister. Remove the solder from the bottom of the canister.

You then want to remove the black "top" from the canister. This will take patience and a very small screwdriver or small pry tool. You will see some "tabs" I believe two of them. Try to bend those back and away. Then remove the black piece from the top.

You can see the lead where it is soldered to the black top. You can cut that lead and remove the solder from the black top. You can now cut the yellow wire on top of the black top. Take a small drill bit and drill out the old thermistor. It will look like this when you are done

Inside the canister is the other lead (wire) that you unsoldered in the beginning. You will need a pair of tweezers to remove it if it hasn't already fallen out. You will see a small home in the bottom of the canister in the center and this is where one lead will go thru and soldered to the canister. This is the Thermistor You will need to carefully bend the leads so it looks like this

take one lead and feed it thru the hole in the bottom of the canister.

You will need to cut the lead towards the bottom of the canister. This is how mine looked after cutting it for reference

I used a piece of tape to hold the long lead to the metal post to hold it in place while I soldered the bottom.

Now strip a very small amount of insulation from the yellow wire. Apply some solder to the bare wire that you just stripped and feed the yellow wire thru the top of the black piece. Now feed the lead from the thermistor thru the bottom of the black piece. Move the black piece down towards the canister. Now solder the wire to the lead

Now push the black top into the canister and bend the tabs back over. You can then snip the rest of the lead that is left over. I then dropped some solder into the top of the black top where the yellow wire feeds into.

Just put the sending the unit back in the tank and now your fuel light will come on when low on fuel and your travel computer QTY and Range will now work as well. Hope this helps someone. Ed

[Rednaxs60]

You've got my attention for another small project. My low fuel light does not come on, and I have the flashing dashes under QTY and Range. I will be looking into ordering the thermistor and try to install. Thanks for doing this.

Cheers

[sportsfreaked]

One thing that wasn't corrected in my post is that its easier to solder the thermistor to the cap first then lower it into the canister thru the hole cut and then solder to the bottom of the can. The thermistor should be in the middle of the canister roughly.

[Rednaxs60]

Thanks for the update. Last fall I decided to run the fuel down to see if the low fuel light would come on. The bike was starting to miss and engine was running hotter than normal, and I was still showing 1 bar on the dash fuel gauge. Decided to fill it up and with the tank being a 21.6 litre tank, I put 21.4 litres into it. I now start looking for a fuel stop when I get to 2 bars, and definitely fuel when I hit one bar. When I fill the tank after showing 2 bars on the dash fuel gauge, I only put in approximately 16 litres so I know I still have a good amount of fuel left.

If I had not stumbled onto your thread, I would just live with it. I now have a way ahead to fix a small issue that is a nice to have.

Cheers

[Rednaxs60]

Checked the QTY and RANGE setting on my travel computer this morning and both are flashing as you mentioned. Thermistors came in yesterday. Now to schedule a time for a fix.

Cheers

[sportsfreaked]

Ernest let me know how it comes out if you would. Doing this should fix your fuel light and your flashing dashes on the travel computer.

I have mine all back together after putting on new progressive air shocks and front fork springs as well as greasing the steering bearing and well now the clutch is dead I have ordered a rebuild kit for the m/c and hopefully that will fix the problem. I have no hydraulic pressure at all so I'm pretty sure the m/c is shot.

Can't wait to hear back from you on the thermistor repair. I know you will do a fine job on it and probably find a way to make it a tad better

[Rednaxs60]

Will post my fix with pictures as well.

As for the clutch MC, rebuilt mine, but it is still not where I want it to be so I will be bleeding the clutch hydraulic again. Lots of places for air to get trapped. I also have an 3 litre ultrasonic cleaner coming for my birthday, my sister is heading up the buy. From looking on other threads and forums, this cleaner should be a valuable asset for rebuilding all sorts of things such as a master cylinder.
Cheers

[Rednaxs60]

Did the fix and did a thread with pictures. So far the travel computer QTY and RANGE functions are working, no more flashing dashes. Letting the fuel drop, expect the low warning light to come on with about 4 litres remaining in the tank, presently at 5.5 litres.

Took about two hours from start to finish. Thanks, your thread was extremely helpful.

Cheers

[sportsfreaked]

Ernest good news I'm glad it is up and working. It's just nice to have that info handy on the travel computer.

[sportsfreaked]

Ernest I am curious to your fuel light come one?

[Rednaxs60]

Chickened out with the first fill up. QTY read 4.5, probably closer to 4 litres remaining. Filled up and put in 18.4 litres. I now have a bench mark and willing to take it down to 2 or 2.5 litres. Hoping this does the trick. Other than chickening out on the light, everything else is working. Down to 6 litres at the moment.

Going to get at the fuel injectors. Have second '85 LTD at my brothers. He is shipping the injectors from the one at his place. I'll clean them then install. Clean the ones I take out and put back in the other '85. Win-win all round.

Cheers

[Rednaxs60]

Went out today and let the fuel drop in the tank. The low fuel level light came on when the QTY indicator said I had approximately 4.0 litres left in the tank. Rode about 2 more Kms and filled up. Put 19.5 litres in the tank. Fuel tank capacity is 22 litres, so I have 2.5 litres remaining when the light comes on. Now I know what to expect.

All indicators for the fuel system are now working.

Good little project.

[Wolf Rider]

Hey Ernest,
Where did you procure the thermister?
I gotta do the same on my Aspy.
I'm not sure if I understand how this works.
Does the gasoline keep the themister cooled?
When the gas gets below the can does the thermister heat up slightly and then go to ground?

[Wolf Rider]

I forgot to ask, does anyone know if the GL1200i has the same sensor as the GL1200a?
Are they interchangable?
Cannibalizing is easier than soldering a new thermister.

[Rednaxs60]

Checked the fiche and the fuel sending units appear to be the same for the Interstate and Aspencade.

Got the thermistor from Mouser Electronics - P/N AMPHENOL ADVANCED SENSORS and their manufacturing part # RL2004-582-97-D1. Good service.

Not a hard job to do. Took me a couple of hours.

Cheers

[WingAdmin]

Hey Ernest,
Where did you procure the thermister?
I gotta do the same on my Aspy.
I'm not sure if I understand how this works.
Does the gasoline keep the themister cooled?
When the gas gets below the can does the thermister heat up slightly and then go to ground?

You got it, that's exactly how it works.

You need to make sure of a few things when replacing it:

- Make sure the replacement is a negative temperature coefficient (NTC) thermistor - one whose resistance DROPS when it gets warm. A PTC (positive) has resistance that increases when it warms up, and will work backwards (fuel light on when it's full, and light goes off when it gets low).

The temperature ranges and resistance ranges should also be similar to OEM.

[Wolf Rider]

Thanks Ernest.
Thanks WingAdmin.
I'm wondering why Honda chose that design. It seems kinda barbaric.
Why not just rig it up to light up the warning when down to one or two bars on the float sensor?
The only thing I could think of is if the float sensor failed, one would still get a warning when the fuel level got low.

[Rednaxs60]

- Make sure the replacement is a negative temperature coefficient (NTC) thermistor - one whose resistance DROPS when it gets warm. A PTC (positive) has resistance that increases when it warms up, and will work backwards (fuel light on when it's full, and light goes off when it gets low).

The temperature ranges and resistance ranges should also be similar to OEM.

Learned something else here. Did not know the NTC - negative temp coefficient or PTC - positive temp coefficient aspect of a thermistor. Always learning. The AMPHENOL ADVANCED SENSORS and part # RL2004-582-97-D are an NTC thermistor.

Cheers

[jimh352]

Came across this thread, and ordered 3. One question before I begin, do you think it's possible to somehow raise the "can" so the light comes on a little sooner?

Rednax, you said it leaves you with 2 liters when the light comes on? That's about 1/2 gallon right? I just think that's too close for me.

I have the 85 Limited.
Thanks guys.

[Wolf Rider]

I believe that the light coming on is directly dependent on when the can dries out, or is no longer emmersed in gasoline.
So yes changing the position of the can will change the point where the light comes on, one direction or the other.
Having said that , make sure that you check and double check when the light is activated and how much range you have left.
You may already be in the wheel house and not realise it.
I doubt that your position will be identical to Ernest's to begin with.
Time can make things sag over 30 years (breasts,door jams,etc) So as they get older the amount of range left in the tank may decrease.
You may not have to change anything and if you do it may take several tries before you get it where you want it.

[Rednaxs60]

As awhardt mentions, the can may not be in exactly the same spot, but close. You will not know when the light comes on until you fix the sender. I would fix the sender then ride until the light comes on. If you are concerned with the fuel level, take a fuel can with you just in case.

You may be able to move the can up a bit to change when the fuel light comes on. 2 litres is just more than 1/2 USG. I'm comfortable with mine as I generally keep the fuel above the last fuel bar, but also know when the light will come on.

The benefit I find from the fix is the travel computer can now be used for fuel timings. I get approximately 370 Kms (230 miles) per tank.

Cheers

[Wolf Rider]

Wow!!
You get 370 kms on a tank?
I must have a problem on mine because I'm only getting 200 kms per tank on my '86 Aspy.
That's mostly city riding and I'm running carbs and not a fuelly like yours.
Maybe its time to change the plugs?

Andy

[Rednaxs60]

Last tour of the BC interior, uphill and down - two up - average 46 MPG.

Cheers

[jimh352]

Thanks guys, I'll do exactly that. Fix first and see when the light comes on. I get awful nervous with low fuel on anything I drive, too many times in my younger days running out. I was wondering if it could be moved, not having seen it up close yet. I just like doing things once, although I've yet to experience it, usually do stuff twice at least, like when I changed my starter, had to put back stuff in a certain order, as in I attached exhaust then had to undo it to wiggle the crash bars in place.

Rednax, wow that is good mileage. I only get 37mpg, but then I have that trike kit on mine. You have the Limited too right? Did you get it new? I just got mine, has 47k miles on it, not too bad of shape. Purrs nice, roars a little but I grandpa it. Oh wait, you talking kilometers? I'll have to Google it, lol.

[jimh352]

Oh yeah, I see now that I got back to the post, 46mpg, as in miles. Told ya I do things twice, my fate.