Hey Scotty, I have a 2003 Nissan Pathfinder bought used currently with 164,000 miles. When I bought it the fuel gauge was stuck in the full position and they told me I needed a new fuel sending unit. I recently replaced the unit as well as a fuel pump which was also going bad but the fuel gauge is still stuck on full. The check engine light is also on with the code that says that the fuel sending unit is bad which remained on even after I replaced it. They're also seems to be some weird electrical issue with the car because when I did the job I disconnected the battery and when I reconnected it the stereo would not work. It eventually started working again but it has been intermittent. It previously had issues with the stereo but it would at least turn on. I'm not sure if the sending unit I got was defective or if maybe there was some kind of weird underlying electrical relay issue.
The fuel sender switch is a variable resistor. (like the dimmer switch on a light)
Turn the dimmer switch knob, resistance increases, current decreases, and the light gets dimmer.
When the sender's float is high in the tank there's less resistance. As the float gets lower it moves the sender switch, resistance increases (like turning the knob on a dimmer switch, and the fuel gauge goes down accordingly).
So now that I'm done answering a question you didn't ask, maybe test the connector plug going to the sender unit.
To rule out a defective sender just unplug the wires at the sender. Turn the key to on.
The fuel gauge will read empty if the problem is the sender and NOT with the wiring or the fuel gauge itself.
If the gauge doesn't move to empty you may want to test the connector plug at the sender.
If the ground is "open" (broken ground wire or bad connection to the terminal in that plug) or the power wire is shorted to ground, the gauge would always read full.
Here's how:
Based on what you says, you may have electronic issues with the BCM. Unfortunately, it is expensive to replace the BCM.
Thank you for your response. I just looked it up and it says average cost is around $500. Does that sound about right?
I googled it and it is a round $700. You also need to reprogram it which is an extra cost depends on where you go to do that.
Yeah I think you might be right from what I'm finding in terms of the symptoms. Looks like it's possible to reset them sometimes though?
Yes, but you need a dealer level scan tool to be able to do that.