Tuesday, October 29, 2013

Low fuel indicator mod in July 2011

One thing that did not work when I bought the Integra was the low fuel indicator. It was not secret, I knew about it from the previous owner since day one.
The low fuel indicator circuit consists of a 1.5 Watt bulb and PTC Thermistor. The PTC thermistor has large resistance value, when submerged in gasoline, the current doesn't flow and the bulb is off. When the thermistor is above the gasoline level it gets hot and the resistance falls down thus allowing the current to flow and the bulb lights up. It is a simple principle. But the PTC Thermistor had broken down.
It was not possible to order just the PTC thermistor from Honda, they only sell the whole low fuel sending unit. That was not the most efficient way to fix things when you are on budget.
First I tried to find a suitable substitute for the PTC thermistor which I found. It had a little bit greater resistance but it worked just fine. Then after a few weeks it broke down again. The same problem.
After this experience I decided to build a simple pcb circuit board that would do the job and be more reliable. It can be also manually dialed to any point at which the low fuel indicator bulb should light up.

PCB board.
The PCB is mounted in this box with connector.
The box with the PCB is mounted underneath the aluminum cover by the low fuel sending unit.
Mounting location of the box.
The schematic of wiring looks like this:

So far it works very well. It was a successful mod.

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