dim check eng light & bright fuel light

[olddog58]

I had one of the earlier PDM's installed and ended up with a variety of issues on my 2008 K9 EFI. I seem to slowly be working through the bugs.
My check engine light has glowed dimly every since the PDM went in. Most people seemed to agree it needs a pull-up resistor for the PDM kit just like the wires plus kit seems to need it. But most everyone said don't worry about it too much. Well now my low fuel light is on and won't go off.
Can the two be connected? Do I have to try again (heavy sigh) to get BDPP to put together a pull up resistor kit?

 

[BigDogBro1]

The CHECK ENGINE LED needs the 10k ohm or so pull-up resistor to apply 5 volts to the signal side of the LED if the active LOW OPEN COLLECTOR (near ground) EHC signal level is not being applied by the EHC. This pull-up would apply 5 volts to the (-) cathode leg of the LED thus turning it OFF. Effectively minimizing current flow thru the LED enough to stop it emitting light. The (+) anode leg of the LED is connected to a 5 volt power source.

The low fuel light function is a bit more involved than just using a pull-up resistor. It's operation is not CONNECTED to the CHECK ENGINE LED operation.

The EHC did some signal conditioning for the thermistor bead in the fuel tank.

A simple explanation of common thermistor operation:
As the fuel level drops, the fuel no longer cools the thermistor in the tank and the small amount of current allowed to pass through it begins to heat it up slightly. When this happens the thermistor bead resistance decreases and at a predetermined circuit designed trip point the voltage across the thermistor is sensed and the LOW FUEL LED is allowed to turn ON.

Wire+ does have a mutli-wire potted module that allows the LOW FUEL LED to function without the EHC when using the Wire+ kit.

If the PDM electronics is poorly designed the thermistor could be damaged over time. The thermistor can self destruct if the circuit current is not correctly limited.

 

[Jwooky]

Great explanation.

 

[olddog58]

That really was a nice explanation.
So first I need to go back to BDPP and keep asking for the pull up resistor.

Big question, is it safe to ride with the low fuel light on? If the sensor inside the tank has failed, is there any chance of a melt down and fire?