Low Fuel Warning Light ELFI Troubleshooting

Hello friends, I have a problem with my ELFI unit for the low fuel warning light. The unit works great for a few years, but today I have got a problem.
The low fuel warning light goes on at the right time, the needle was on the beginning of the red field in the fuel gauge. I drove to the gas station and make my tank full of gas, but the low fuel warning light goes not out!! The needle show me a full tank.
Has anybody an idea, what can I do?? Thanks a lot for your help!!

Greetings from germany

Bob (1969XR7Vert) will be along shortly and he will be able to answer the question. He designed and built the ELFI.

This is really nice to hear, thank you very much for your response.

A long-shot, but needs to be looked at anyway…

By any chance, did you work on the wiring at the starter solenoid in the engine compartment? The low fuel system has a “prove-out” circuit using a red wire with a ring connector that needs to go onto the starter side of the solenoid. Some people inadvertently put it on the battery side. A clue that this might be the case is if the light is still on when the key is off.

I didn´t work on any wiring in the engine compartment!! When the key is in the off position, is the low fuel warning light out. The warning light worked absolutly correct, the prove out function worked and the light goes on when the needle was at the beginning of the red field. Everything was perfect till yesterday!!


Based on what you have described, it sounds like something may have failed on the ELFI board. However, there are a number of checks you can make:

  1. Is the ELFI board properly grounded?
  2. Measure the voltages on each pin and report back. With the ignition switch in the run position and a full (or above the red mark near E), you should have:
    12V on the 12V pin
    0V on the ST pin
    0V on the LF pin (but you will have ~12V since the LF lamp is on
    5V on the SSIVR pin
    Something below 4.1V (much lower with a full tank) on the Gauge pin



Hi Robert, thanks a lot for your help!!
I have done the measurements, my results are: (my tank is compl. full)

  1. Ground of the ELFI is ok
  2. on the 12V pin I have 12,24V
  3. on the ST pin I have 0,08V
  4. on the LF pin I have 10,84V (lamp is on)
  5. on the SSIVR pin I have 1,49V, when the needle starts to grow up (empty position)
    when the needle stops on the end of the fuel gauge (full position), there are 0,15V on the SSIVR pin

Best regards

Hi Martin,

  • Regarding your #5, SSIVR should have 5V on it anytime the ignition is on. Could you recheck this and report back?
  • What does the Gauge pin of the ELFI read (or is that what you reported as SSIVR by mistake above)? The Gauge pin should be a low voltage when the tank is full and go up as the fuel level decreases. At the low fuel threshold (where the LF lamp lights), the Gauge pin voltage should be around 4.10V



Hello, I have done the measurements again. For checking my self and to avoid mistakes. I was a little bit unsure after your last post.
From my point 1 to point 4, nothing has changed. But in point 5 I have done a mistake!! So I would like to give you a new explanation for that point.

I have measured 4,99V on the red wire/SSIVR pin, at anytime when ignition is on.

On the black wire/Gauge pin, I have measured 1,74V with the needle of the fuel gauge on the full mark.
When the needle stands/starts on the empty mark, I measured 1,92V.

I hope that helps to figure out there the problem is!?
Thanks Martin

Okay, that sounds better, except the 1.74V and 1.92V measurement on the Gauge pin. Your fuel gauge continues to work correctly? If yes, the voltages you mention for the Gauge pin do not make sense. If the gauge is at the transition into the empty area (beginning of it), the voltage at the ELFI Gauge pin should be around 4.1V.

So if your gauge is working correctly but the ELFI is not, check the voltages at: 1. the fuel gauge, they should be 5V (SSIVR voltage) on one stud and ~4.1V on the other when the gauge is at the LF transition area. And then 2. the voltages at the ELFI (SSIVR and Gauge pins), they should match what is on the fuel gauge studs always because of the two-wire ELFI harness connections between the gauge and the ELFI.

I have measured in 2 ways, one time with connected wires (red and black) and the other with disconnected wires.

On the studs of the fuel gauge with disconnected wires:
the inner stud (SSIVR/red wire terminal) 4,99V
the outer stud (Gauge/black wire terminal) 1,92V (needle at low level) - 1,74V (needle at full level)

When the wires are connected, you can measure the same values at the pins on the ELFI.

On the disconnected wire ends, I have measured:
SSIVR/red wire 1,46V / Gauge/black wire ~0,2V

Is it possible, that the fuel sending unit stands out of the readable range?
Because the fuel sending unit is the only thing which has changed something, during the refuelling process.

On the studs of the fuel gauge with disconnected wires:
the inner stud (SSIVR/red wire terminal) 4,99V
the outer stud (Gauge/black wire terminal) 1,92V (needle at low level) - 1,74V (needle at full level)

This still does not make sense. Again, is the fuel gauge working properly? I do not see how it could be with the voltages you are reporting. Needle at low level should be around 4.1V. This needs to be understood.

Having said that, the ELFI should have the LF lamp off at both of these voltages, assuming they are both positive. You say 1.92V and - 1.74V, MINUS 1.74V? If you are actually measuring -1.74V, this too is a problem and needs to be understood. That would make me think there is a ground problem, no where in this system should you measure NEGATIVE voltage. Please clarify that.

I measured no neg. voltages anywhere!! The - is a hyphen and should mean from 1,92V to 1,74V!!
Why should the fuel gauge suddenly doesn´t work? How should I know, if the fuel gauge works proberly?
The only thing is, that I can see that it works!
Because the needle goes down, when the key is off. And the needle goes up, when the key is in starting position.
Why should the LF lamp be off, at both voltages??
It is on at both voltages, because you say that more than 4.1V is need to shut down the LF lamp.
The LF lamp lights the whole time, with connected or disconnected wires. It is out, when the key is in off position.
I do a test tomorrow. When I give a little bit more than 4,1V on the gauge pin/black wire, the LF lamp must go off.

Okay on no negative voltage measured.

Actually, the LF lamp should be off when the Gauge pin is BELOW 4.1V, the LF lamp should come on when the Gauge pin voltage is 4.1V or higher.

The reason I keep asking about the voltage range at the gauge is because the gauge cannot work properly if the voltage at the sender pin is not higher than 1.92V at the low level.

The gauge operation aside, the ELFI should have the LF lamp off at both of these voltages as I mentioned. So, if we ignore the voltage you report at low level, it would say that the ELFI has a failed component. It is just hard to ignore the voltage at low level! but, if you say the gauge works normally, we can assume it is a problem with the ELFI.

If you would like to send the unit back to me for repair, I will PM you my address.



Hello Robert, sorry for the delay.
Thanks for your offer, to send the unit back to you for repair. I would like to do that, please PM me your address.
I have done the test, which is discribed in the installation manual. But the LF lamp will not go out!!
The only thing which I can tell you is:
When the voltage is 4.1V or higher at the gauge pin, the LF lamp lights a little bit brighter.
And when I tab the gauge pin to ground, the LF lamp lights a little bit darker.
When I do the prove-out function, the LF lamp lights also a little bit brighter.

Best regards

Check your PM’s Martin.