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04 S3 - fuel light intermittent fault

2K views 16 replies 5 participants last post by  Billy10 
#1 ·
Light comes on sometimes when tank full.

Haynes manual in fuel level sensor seciton says you can replace the float in the fuel level sensor, but I can't see the part in the parts diagrams.

Would be grateful to know 1. if any one else had this issue, 2. how to resolve, and 3. if I need the float, where can i get it?

any advice appreciated. cheers
 
#2 ·
Take the fuel panel off of tank and see if float is still there. If it is I would get e new sensor. My RS would show empty at half tank from time to time. Since it’s British prices go from arm to first born. Other people will chime in with more info. 04 is 15 yrs old and with the bad fuel these days thugs croak quicker,
 
#4 ·
There's nothing wrong with the sensor - it is common issue on the S3/Daytona of this series.
It's due to the way the sensor is wired, causing a ground loop when the resistance of the sensor is at its lowest (when the tank is full).
You will find you get the error when tank is full but after level drops a bit, the light will go out.
I've written several responses on this, with a potential solution to amend the wiring to be the same as the Sprint (which shares same sensor but does not have this issue)
There was a service bulletin about this back in the day ............
Will try to find that for you later (in the meantime try search on fuel sensor under my name)
edit - here it is - https://www.triumphrat.net/daytona-...-fuel-light-after-filling-up.html#post7730394

The simplest way to resolve the issue (although involves removing/draining tank) is to physically restrict the float from coming to the 'full' position by limiting its travel with a tie-wrap around the sensor board - the sensor only cares about the 'low' or 'not-low' status, with 'not-low' being any position above the low level threshold. So whether the ECU sees the resistance reflected by half-full when tank is full, is moot. Hence it is OK to restrict the level to which the float can rise.

Externally, you could also try adding a small resistor in series (5 - 10 ohms or so - the lowest value that turns the light off is what you want) - that would cause the actual low level warning to come on a little earlier.
 
#7 ·
edit - here it is - https://www.triumphrat.net/daytona-...-fuel-light-after-filling-up.html#post7730394

The simplest way to resolve the issue (although involves removing/draining tank) is to physically restrict the float from coming to the 'full' position by limiting its travel with a tie-wrap around the sensor board - the sensor only cares about the 'low' or 'not-low' status, with 'not-low' being any position above the low level threshold. So whether the ECU sees the resistance reflected by half-full when tank is full, is moot. Hence it is OK to restrict the level to which the float can rise.
Thanks again for this. Have removed fuel pump housing anyway so doing this at same time. What is the easiest of the two options? Re physically preventing the fuel level sensor reaching full, not clear to me if/how to do it. One of the posts in thread you linked ot above says:

"That's what I thought, and exactly what I was planning on doing, but there is no float in mine at all, just a row of tubes with what looks like a diode in between each one, and as mentioned, my multimeter reads open circuit across the sender regardless of fuel level"

I haven't removed the fuel level sensor but it looks like a sealed tube at first glance.

If I wanted to match the wiring to the Sprint's, how would I do that? Am guessing this route will be a tough one for me to try.

Help much appreciated
 
#9 ·
The fuel level sensor housing is quite firm, so one option would be to drill a hole through it say 1-2 inches form top and feed a zip tie through to prevent float rising. Any reason that wouldn't work (including zip being suitable in solvent)?
 
#11 · (Edited)
Ah, many of us have benefited from DEcosse's 955i fuel sender fix.

Pull the sender. Pop top off. Look inside for sensor board and float. Drill hole across and put cable tie through to stop the float going all the way to the top. Snap top back in place. Re install sender, tank etc. ride to servo, fill to brim, marvel at lack of low fuel light when tank is full and worry if it'll come on again when the fuel is actually low.

Quick and dirty mark-up attached.
 

Attachments

#14 ·
Issue now resolved. Was not the problem described above. The float had stopped moving freely inside the tube. ...
I would suggest that has NOT fixed the problem
Sticking float would have the opposite effect - you might never see the low level if it was sticking above the low level threshold point;
but coming on intermittently when full cannot possibly be caused by a sticking float regardless of where it was stuck (well unless it was stuck at the very bottom)
It will be back :D
 
#17 ·
Initially problem was intermittent. It came and went. Most noticeable with a full tank. Just before tank came off a few months ago (for a number of other jobs) light came on permanently. While tank was off I did the restriction mod as it was free! Put sender back in, cable tie through it, then reassembled. Problem didn't go. So then I bought a replacement sender. As soon as I got it I noticed the float moved differently. Only had chance to reinstall recently so posted after that.

Didn't do the restriction on new sender as wanted to see for sure what the problem was. But I suspect I will need to do it in the future. Having done it once already will be pretty quick to do if/when.
 
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