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THIS DISCUSSION / SOURCE-DERIVED OVERVIEW
Discussion summary
YOUR RESEARCHErratic fuel gauge
Leading reported evidence
Check resistance and it checks out too
Performed · outcome unconfirmed
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Read evidence and context
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Performed · outcome unconfirmed · Original poster
Just a small update on this, I pulled the sender out and all looks fine, checked the resistance and it checks out too.
Leading evidence: 'Check resistance and it checks out too' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, The most frequently discussed action is 'Check plugs' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Suggestion · Original poster
Sorry, I haven't found a solution yet, although apart from checking sender and checking plugs on back of cluster I haven't tried very hard.
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Suggestion
1st thing I'd do is check the resistance from the tanks sender unit in the frunk.
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Suggestion · Original poster
Sorry, I haven't found a solution yet, although apart from checking sender and checking plugs on back of cluster I haven't tried very hard.
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Suggestion
It's typical for them to use a voltage divider circuit to create a voltage that is proportional to the sender resistance then use an ADC to measure that voltage (there are specialist chips that can measure current with a fixed voltage across the sender, but this is unlikely in an automotive implementation).
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Suggestion
It's typical for them to use a voltage divider circuit to create a voltage that is proportional to the sender resistance then use an ADC to measure that voltage (there are specialist chips that can measure current with a fixed voltage across the sender, but this is unlikely in an automotive implementation).
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Suggestion
It's typical for them to use a voltage divider circuit to create a voltage that is proportional to the sender resistance then use an ADC to measure that voltage (there are specialist chips that can measure current with a fixed voltage across the sender, but this is unlikely in an automotive implementation).
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15 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
911uk: 1 discussions
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Generation: 20261026T205155Z · outcome-qualification-6. Deterministic extraction; no AI model inference. How we use sources
Hi all, I have a new issue where my fuel gauge is all over the place, mostly high, mostly way off the scale. Has anyone had this issue? Wondering if it’s a sender or cluster problem.
I did do a search and there is loads of threads about calibration,
refuelling strategies etc, but I can’t find anything about this.
I don't think it will be sender. It's an electronc cluster so will interpret the sender voltage as 0-100% then display that on the gauge. The gauge/cluster would have to be broken to go beyond 100%.
The sender will be part of a voltage divider circuit. Microcontrollers can't directly measure resistance, they either measure voltage or current.
It's typical for them to use a voltage divider circuit to create a voltage that is proportional to the sender resistance then use an ADC to measure that voltage (there are specialist chips that can measure current with a fixed voltage across the sender, but this is unlikely in an automotive implementation).
Regardless of how you think it's measured, if the resistance from the sender that it outputs is altered, then the gauge follows suit. All I'm suggesting is illiminate the sender by measuring the resistance from it. When I made mine adjustable, from doing some calculations, 1 gallon of fuel in the tank equated to 25 ohms (but not 100% linear over the full range). Half a tank is around 220 ohms and the lower the fuel level, the higher the resistance.
Hope this helps.
Thanks Alex for the resistance figures, gives me an idea of what to look for. Car is pretty much full at the minute, so I should expect to see a low resistance reading, would it be 0 at full tank do you think?
I've just read elsewhere that its range is 240 to 33 ohms
Edit: the ohm figures I quoted on my previous post were for the C4 which has a different sender unit due to the shape of the tank.
Just a small update on this, I pulled the sender out and all looks fine, checked the resistance and it checks out too. I was getting a reading of ~300 ohms for empty up towards near zero for a full tank and was linear through the range, so confident enough to say the sender is fine.
I suppose next step would be to see what reading i am getting at the back of the gauge cluster. Looking at the wiring diagram the other side is connected to the analog ground, does anyone know what the significance is of the term 'analog' is, surely a ground is just a ground?
I'm having the same issue in my 2000 Boxster S. Fuel needle has gone crazy. It has actually fixed itself once, but seems to return when I refill. Sending unit seems fine. My guess is something is physically damaged in the needle mechanism itself - the main tell is that it doesn't return to empty when ignition is off. Have you had any success in finding a solution? I'm hoping the answer isn't a cluster replacement.
Sorry, I haven't found a solution yet, although apart from checking sender and checking plugs on back of cluster I haven't tried very hard. Should the gauge go to zero when ignition is off? i didn't know that. It appears no one else on the internet has had this problem, so welcome to an exclusive club
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