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Just happened recently. As far as i know it was working prior to filling it up.. filled it up and started it and the gas light is on and the gauge is at the red line in empty. I pulled a few wiring diagrams for it and found 3 wires going from the TIPM to the fuel pump module. B+ to fuel pump, fuel level signal, and sensor ground. However i was unable to access the plug because it is above the fuel tank. I was able to get to the grommet in the floorpan from under the back seat that ran from the fuel pump connector to a connector inside, but i would have had to backprobe the wires to be able to get an accurate reading. My thought process was to ground the signal wire and see if the gauge moves.. thus eliminating any wiring / module issues from that point forward to the TIPM. Also there was no check engine light, and no codes stored or pending.
I know its probably a faulty sending unit, but i don’t like to throw parts at a car. I want to be sure that this is the problem 100% before doing so. Also this is a friend’s car so i will not make him pay for something without being sure.. not to mention draining a full tank of gas, dropping the tank and possibly replacing something that is not the problem.
Any ideas exactly what to check from here? Ill upload the wiring diagram I used so that may aid in assisting me. I only looked at the car for about a half hour, but had limited resources and not much time.
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Generally if the gas tank light and the gauge both falsely show empty then it is the sender. If just the gauge and not the gas tank light, then it is a problem in the cluster. Your logic is good to check the wiring and grounding the sender signal, because the problem could actually be the computer (PCM). I have heard of quite a few cases of the computer being the problem on Liberty models with this symptom. If it turns out to be the computer, that can cost big money, as it has to be a new computer module ordered from (and programmed by) the Chrysler factory with the VIN, VIN-specific options, and mileage. No one else can program these, not even the dealership service departments. Your friend may decide just to not fix it and refill the tank by watching the odometer and refueling every xxx miles. Hopefully it’s just the sender or a wiring fault. If you find that you need to drop the tank, have your friend continue driving the vehicle until the tank is nearly empty first.
Thank you for the reply, I appreciate your input. I also forgot to mention that i did the cluster self test (hold trip button with key off, turn key on, release button) and all of the needles and lights worked in all positions so im fairly certain that the cluster itself is ok. Its just something on the control side thats not letting it see the proper fuel level.
Im guessing the easy (although not so easy) test is to gain access to the fuel pump module connector and try grounding the signal wire. I also have access to an Autel Maxisys Pro that will allow me to monitor PIDs on different modules. Im guessing the ones i am looking for are fuel level in % and sensor voltages. Also i just read the following in Mitchell:
I am wondering if somehow it was overfilled and is causing a false reading. I sort of doubt that is the case, but it was interesting to read that it will show a low fuel level, even if it is overfilled.
Right. I didn’t think it would be a cluster problem either, I just included that bit for the sake of completeness. The part about receiving more than full messages is true, except the needle would go from empty to full, then after about 5 seconds, it would drop back to empty. If it isn’t moving at all, this isn’t the condition. Before the tank was filled, did the vehicle pass over any large bumps, obstacles, or pot-holes that could have jarred or pinched the wiring? Also, try reading the resistance between the signal and sensor ground rather than grounding it (a short to ground may confuse the computer and cause it to shut off the gauge, and won’t rule out the possibility of an existing wiring short to ground). The specification says the resistance should be between 5 (full) and 270 (empty) ohms (in reality, full is around 15-20 ohms, so overfilling the tank won’t push it outside the range). Outside of that range would confirm a bad sender, where zero or infinite could confirm a wiring fault (but the wires would have to be checked for continuity to rule out an open or shorted sender).
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