I’m the owner of a 1999 Dodge Ram 2500. It is 4x4 and has the 5.9 360 V8. I purchased it recently for a great price. The previous owner informed me the fuel gauge did not work. I have researched online forums regarding the fix for the fuel gauge.

Two weeks ago I swapped out the entire fuel pump assembly with a brand new pump and sending unit from Napa. It did not fix the fuel gauge issue and it remains on E.

Holding down the trip reset button and turning the ignition on checks out as all my gauges function normally through the gauge test. The odometer is off from the actual mileage of the truck which tells me the cluster has already been swapped out trying to resolve the issue.

I pulled wiring diagrams and applied dielectric grease to the connectors on the instrument cluster, C3 connector on the PCM, and connectors on the drivers side front fender well with no luck.

Interesting facts about the fuel gauge: When I hook up my OBD II code reader to the truck and erase codes( even though there is no code) the fuel gauge will immediately rise from E to Full, but will fall back to E a few seconds later.

When driving around town the fuel gauge stays on E. If I pull up to a stop sign and hit the brakes the gauge will climb to Full and then fall back to E.

I have been using the trip to determine my mileage but having the fuel gauge busted is driving me nuts.

Any help would be greatly appreciated, thank you.

 

Ok some of your symptoms are really weird but I'd still start with the basics of tracing every bit of wire from the tank to the gauge. If you ground the sender wire at the tank plug, does the gauge peg full?

Does anyone know how the plug is setup? Does it supply a dedicated ground feed for the gauge, too? If so, I'd be suspect of this ground. The sending unit needs a good ground. It then feeds that ground through the sending unit and increases or decreases resistance based upon float arm position and feeds that modified resistance to the gauge.

I don't know what ohm range Chrysler used here but that's not really important just yet. I thought Chrysler often preferred a weird 30 to 130 or some such.....but again, not really important.

edit: do what HeyYou says below!!

 

On yours, the PCM sends a voltage to the fuel level sensor, the sensor modifies the signal, (variable resistance) and it returns to the PCM. The PCM tells the cluster what to display via the communications bus. If your other gauges are working, then the com bus is doing it's job. I would be curious to see if the PCM was actually GETTING that return signal from the level sensor..... Connector 1, pin 4 at the PCM. Black wire with light blue trace.... (if it's the same as the 98......)

 

I connected a wire tap on the black wire with light blue stripe right before it enters PCM connector 1. Using my multimeter, how should I be testing this wire?

 

Test for voltage between that wire and ground. (ignition on.)

 

I am getting 0 volts to that sensor return wire when running the multimeter positive lead to the wire itself and the negative lead to the negative terminal on the battery. Ignition on.

 

That's not a good sign.... Verify you are getting power TO the sensor, down at the tank... On mine, there is just enough room to stick your hand in there to disconnect it from the fuel pump module.....

You want the Dark Blue/White wire, pin 3 at the fuel pump. Should be 5 volts there.

 

Yes sir I have power there. I unplugged that connector on top of the fuel pump earlier today and was testing it with my multimeter. When I ran a dummy wire from the blue/white wire to the black/blue wire it (with it disconnected from the fuel pump) it would move the gauge from empty to full. I put some dielectric grease on the plug and plugged it back in. Now, instead of my fuel gauge always being on E it has been pegged at full and has yet to drop down.

 

Do a cluster test. Hold the Trip/Rest button, turn the ignition On, wait for the test to start, and let go of the button. All the lights will come on, and all the gauges should go thru their full sweep. Hopefully, that will get the gas gauge to loosen up again.

You did remove the jumper wire? Right?

Test resistance across the pins for the gauge. Should be some reasonable number. If it read infinite, sender is bad. If you get some reasonable value, that would suggest the return wire is broken somewhere.

 

Lol yes sir the jumper wire is removed. Fuel gauge is still pegged at full. Did the gauge cluster reset; All the gauges checked out fine.

On a good note, I went to remove the wire tap off of the black/blue stripe wire before PCM connector 1 and noticed it was not pierced all the way through. I crimped it fully with pliers and ran my multimeter on it. It is now showing .09 volts when the ignition is on.