Low Fuel Indicator & Fuel Level Gauge GL1500

[CRAFFS]

After replacing the fuel pump & filter I took the bike for a run when I noticed that the FUEL LEVEL GAUGE (on dashboard) does not work (at least 10 liters of fuel in the tank). Back at home I removed the fuel pump assembly and checked the float level movement by moving the float arm up & down several times. It moves freely and after a few minutes (with ignition on) still no fuel level "indication" on the gauge.

I emptied the tank to check if the LOW FUEL (reserve) INDICATOR LAMP (on dashboard) comes on. Nothing... When I switched the ignition on, the indicator lamp comes on and off after a few seconds (as it should do). So, at least the lamp "works". I checked the power supply (fuse) that "supplies" both sensors (fuel level & low fuel). It was fine but I replaced it anyway. My manual does not show any "trouble shooting" guides for this issue.

I will appreciate any suggestions. Thank you, Johann

[Erdeniz Umman]

Do you have N light and oil pressure light as supposed to be?

[Rambozo]

One thing to keep in mind for the low fuel light, is that it takes a few minutes to come on, and when it does, it starts off dim then gets brighter. This is because instead of a float switch, it uses a thermal sensor that is kept cool by the gas in the tank, then when the gas no longer covers it, it slowly warms up and allows the light to come on.
As to the gauge, you can check the function of the float with an ohmmeter.

[bellboy40]

Try swapping out the #3 Tail main relay with another one. The air pump relay would be a good one. Then see if it works.

[CRAFFS]

ERDENIZ, yes, the N Light & Oil Pressure Light work as it should be.

RAMBOZO, I checked the Low Fuel light as you described but no "reaction'. Regarding the Fuel Level Gauge, I have in the meantime found how to do the test with the ohmmeter and what the readings should be. I will do the test during the weekend. Thanks a lot for all the info.

BELLBOY40, that is an interesting test! I am not knowledgeable with electrics/electronics ( but I will definitely "find" those relays and do the test (swapping the relays) during the weekend. Thanks for the advice!

[Erdeniz Umman]

Based on the information you have given so far and the circuit diagram, I don't see an interrelated problem at fuel gauge and fuel low light.

If you haven't removed their connectors and forgetten to reinstall, then it is just a coincidence to have these problems at the same time.

So you should troubleshoot these problems separately.

[CRAFFS]

Erdeniz, I agree with you. I must mention that the bike was not used for a few years and unfortunately with very little fuel in the tank. In other words, both sensors were exposed to "air" for a long time - I don't know if that could have caused "damage" to the sensors?. I checked all connectors including "earth wire" connections I will do the checks the other gents advised and hopefully find something...

[DenverWinger]

Easy enough to check the both sensors.

If you put a ground wire to the connection on the tank for the gauge, the gauge needle should move to full scale. Ground the connection for the thermister and low fuel light should come on. Be careful not to put a ground on your fuel pump connection, that could be very bad.

These tests will tell you if the problems are inside the tank (good response) or elsewhere (no response).

[CRAFFS]

Hi DenverWinger, thanks for your reply. I have already checked the thermister and the low fuel light comes on (as should be). I will today/tomorrow check the fuel gauge as you described. Should the gauge needle moves to "full", does it mean there is a "loose" connection "somewhere"?. (actually, this question may apply to the thermister as well?).

[DenverWinger]

Ya, If you ground the gauge connection at the fuel tank, and the needle goes to Full that means the Bike circuitry and gauge are OK and the problem is inside the tank.

[CRAFFS]

Hi DenverWinger, Erdeniz, Rambozo, Bellboy40,

1) I grounded the gauge connection at the fuel tank and the gauge goes to Full.

2) As mentioned previously, I did the same with the Low fuel sensor and the lamp goes on.

So, both circuits are OK. I just find it "strange" that both Fuel level & Low fuel sensors "packed up all of a sudden"?

I have also checked the Fuel Level sensor with an ohmmeter, only reading I get is -1

I still need to swap #3 Tail main relay with the air pump relay (as "bellboy40" recommended). If this does not work, do you know if there is anything else (mechanical?) that can be checked or shall I just order a new units?

[Rambozo]

Check the ground that goes to both sensors. Make sure it really has a ground connection.

[Erdeniz Umman]

I don't think there is a ground problem.
Check the resistances of the sensors as described in the service manual below.

[bellboy40]

Hi DenverWinger, Erdeniz, Rambozo, Bellboy40,

1) I grounded the gauge connection at the fuel tank and the gauge goes to Full.

2) As mentioned previously, I did the same with the Low fuel sensor and the lamp goes on.

So, both circuits are OK. I just find it "strange" that both Fuel level & Low fuel sensors "packed up all of a sudden"?

I have also checked the Fuel Level sensor with an ohmmeter, only reading I get is -1

I still need to swap #3 Tail main relay with the air pump relay (as "bellboy40" recommended). If this does not work, do you know if there is anything else (mechanical?) that can be checked or shall I just order a new units?

There is no need to swap those relays since the gauges work when you ground them at the fuel tank. You are getting the supply voltage needed to operate those gauges. The trouble for the fuel gauge not working is likely going to be the resistor that the float arm operates. You might could remove it and spray some contact cleaner in it while moving the arm up and down and see if that will get it working.

[CRAFFS]

Thanks Gents for all your advice & recommendations.

Erdeniz, thank you for the service manual pages, it is a great help - my (stupid) manual (which I downloaded) just show how to remove the units but does not give the "resistance values" (ohms).

I have again removed both Low Fuel sensor & Fuel Level units from the tank. I checked the resistance (ohms) of both units but get "funny" readings. I suspect my multimeter to be faulty and will take the units to an auto-electrician today to be tested.

By the way, the Fuel Level unit (bracket & resistor) is quite "rusty". I cleaned it as well as I could and thoroughly sprayed the inside of the resistor with "ElectroClean" and left it overnight. Checked it again this morning (ohms) while moving the arm up & down - still same "funny" readings. On my way to the auto-electrician....

[DenverWinger]

Try soaking the fuel level sensor in vinegar or one of those "Calcium-lime-rust" household cleaners overnight, that might fix it nicely.

As to the low fuel thermistor, it either works or it doesn't. Unless you can find a bad/corroded connection in the wiring to it somewhere. You can test it out of the bike, connect it in series with a #194 light bulb to 12 volts, if not submersed in liquid and allowed to warm up the light bulb should slowly light up and get brighter.

[AZgl1800]

CRAFFS


sent you a PM,

look for it.

[CRAFFS]

Good morning Gents (yes, indeed a good morning), I have a perfectly working Fuel Level sensor/gauge!

Just some feedback: - I went to an auto electrician and he checked both Low Fuel & Fuel Level sensors (ohms). He got the same "silly" readings I got with my multimeter. He checked my multimeter and found it to be perfect. His recommendation;- Replace both units...

Came home and saw DenverWinger's message - "soak the Fuel Level sensor in Vinegar and leave overnight", which I did (also removed the metal cover over the resistor). In the meantime I re-checked all connections, proper earths etc. as recommended by you Gents. Next morning I took the Fuel Level unit from the Vinegar "bath". Carefully wiped it off, rinsed it in water and dried it properly with a hairdryer set at low speed & low heat. Could not believe - what was a "rusty/dirty" unit came out brand new! This stuff (vinegar) really works!! Checked the ohm "values" by moving the float arm up and down - prefect readings!

I did the vinegar treatment with the Low Level sensor as well, it came out like new but still "dead" (will replace it at some stage). Re-installed everything and with ignition on, started filling the tank and watched the Fuel Gauge needle climbing to full!

All body plastics etc. fitted, within the next hour I am on my way to do the "four passes" trip (where I live we are surrounded by mountains with beautiful passes & scenery).

a Great THANK YOU for all your help and patience to bring my bike back to life!. I have learned a lot during this process. If any of you need help on the GL1500 fuel system, please contact me, I am an expert! )

[DenverWinger]

Glad to hear of the success!

There's a thread here somewhere about replacing the low fuel thermistor with a float. Think it's in the 1500 How-to section.

Thinking about doing that to mine, although the low fuel thermistor works, I think it's "out-of-tolerance", when fuel is low and the bulb lights, it is very dim and is not very visible in the daytime.

[CRAFFS]

Thanks for the tip, I will check it. I also saw a video on YouTube how they replaced the thermistor with an "aftermarket" unit. It may be an option.
Thanks again for the vinegar tip. Think I must bottle & market it under "Denver Holy water" ).

I did 2 mountain passes this morning. The bike runs smooth and strong, what a pleasure. Me & the missus are planning a 2500Km trip along the Cape east coast towards the end of the month. Looking forward!

[bellboy40]

This is a link to the how-to article about replacing the low fuel sensor with the float switch that DenverWinger alluded to.
viewtopic.php?f=14&t=11167

[CRAFFS]

Good afternoon "bellboy40",

I noticed now that my reply to your last message was not posted?. Will try again;- I have checked that thread regarding replacement of the Low Fuel Sensor (same as DenverWinger recommended). Looks like a good option. As my electrical/electronics knowledge is limited to replacing a light bulb, I will discuss this thread with an Electronic technician living near me. Thanks for the info!