2005 fuel gauge issue

[DougWahler]

I am having issues with my fuel gauge. It reads full (even though it's not) and then will suddenly go to empty and the alert will sound. I am trying to determine what the issue is. What should the gauge read with the connector to the fuel pump read (full or empty)? Dose anyone know the pin out for the connector at the fuel pump and what I should check? Any help here would be greatly appreciated. Trying to avoid dropping the tank out to check the float.

2005 Ram 2500.

 

[Bob4x4]

Here you are
CAV CIRCUIT FUNCTION
1 Z201 12BK/OR GROUND
2 K900 18DB/DG SENSOR GROUND
3 N4 18DB/WT FUEL LEVEL SENSOR SIGNAL
4 A109 14OR/RD FUEL PUMP RELAY OUTPUT

 

[Bob4x4]

For Fuel Gauge Operation: A constant input voltage source of about 12 volts (battery voltage) is supplied to the resistor track on the fuel gauge sending unit. This is fed directly from the Engine Control Module (ECM). NOTE: For diagnostic purposes, this 12V power source can only be verified with the circuit opened (fuel tank module electrical connector unplugged). With the connectors plugged, output voltages will vary from about .6 volts at FULL, to about 7.0 volts at EMPTY. The resistor track is used to vary the voltage (resistance) depending on fuel tank float level. As fuel level increases, the float and arm move up, which decreases voltage. As fuel level decreases, the float and arm move down, which increases voltage. The varied voltage signal is returned back to the ECM through the sensor return circuit.

Both of the electrical circuits between the fuel gauge sending unit and the ECM are hard-wired (not multi-plexed). After the voltage signal is sent from the resistor track, and back to the ECM, the ECM will interpret the resistance (voltage) data and send a message across the multi-plex bus circuits to the instrument panel cluster. Here it is translated into the appropriate fuel gauge level reading.

 

[DougWahler]

Thanks for the information. After checking the wires I ended up dropping the fuel tank and pulling the pump out. I checked the float and the resistance moved from about 10 ohms to 240 ohms, so it appears to be working. So, now I am guessing the issue is with the ECM. I have run the diagnostics on the instrument cluster and all appears to test out normal and no codes. Is there anything else I should check before looking to get a replacement ECM?

 

[Bob4x4]

Test wiring continuity,especially through the connectors.The connector under the cab gets blasted with all the road debris

 

[PWong]

Thanks for the information. After checking the wires I ended up dropping the fuel tank and pulling the pump out. I checked the float and the resistance moved from about 10 ohms to 240 ohms, so it appears to be working. So, now I am guessing the issue is with the ECM. I have run the diagnostics on the instrument cluster and all appears to test out normal and no codes. Is there anything else I should check before looking to get a replacement ECM?

Check for 12V with connector unplugged.
Then check for 0.6V and 7V with connector plugged.
Just checking the resistance of sender was not good enough.

 

[PWong]

Thanks for the information. After checking the wires I ended up dropping the fuel tank and pulling the pump out. I checked the float and the resistance moved from about 10 ohms to 240 ohms, so it appears to be working. So, now I am guessing the issue is with the ECM. I have run the diagnostics on the instrument cluster and all appears to test out normal and no codes. Is there anything else I should check before looking to get a replacement ECM?

Check for 12V with connector unplugged.
Then check for 0.6V and 7V with connector plugged.
Just checking the resistance of sender was not good enough.

 

[TGVET]

Recently, I have ran my tank down to the point the FUEL light comes on. Not my normal MO as I usually fill up at a 1/4 tank but not too worried since I use good fuel filtration. Anyhow, couple times now of late, I would fill up (28 to 31 gals) tank is 34, and upon leaving the station, my gauge would not bounce back up to full or, even move with key on while filling. (My first indication something amiss). Then, after driving a bit, shutting off and restarting all is fine. Don't know if its time for a new float switch or something else is going on.