Expert: Roland Finston - 6/26/2011

Question
QUESTION: I have a 2000 Chrysler sebring that has a fuel gauge that always reads full. Actually Roland has answered this question already, but I still haven't resolved the issue, so I'm hoping you can help. I pulled the tank unit out and tested at the back of the dash plugin on the dark blue wire to ground with my ohmmeter while moving the float up and down. I got 59 ohms at full and 1048 at empty. This seems ok, so I assumed I needed a new dash unit. I bought a used one from the salvage yard and it does exactly the same thing. I also tried to just switch the gauge from one cluster to the other. Still reads full. Am I missing something? It doesn't seem likely that both clusters would do the same thing, but I have no way to be sure that the used one I bought is good. I don't want to buy a new one if I don't have to. Did Chrysler have problems with these? The mileage is only about 60,000 on my car. Seems like the gauges should still work.

ANSWER: Hi Greg,
According to the '00 Sebring convertible manual (I assume this is the convertible, correct?) the resistance on the wire from the tank goes to the body control module and thence after being digitized and put on the bus it goes to the cluster. I wonder if the dark blue wire from the tank is shorted to ground so that the body pin is 'looking' at O ohms at all times which would be a 'full' reading on the gauge. You can look at the wire at the tank, disconnected of course, and see what is shows as resistance to ground, and with the battery disconnected just in case there would be some sort of power to the bcm otherwise. It is also possible to pull the 20-wire black plug at the bcm and find the wire at pin 15 and see what is shows at that point after unplugging it. I am not sure which is more accessible, the tank plug or the bcm plug but either way that would explain an always full reading.
Roland
PS: Please 'rate' my answer and give me a nomination for 'voluteer of the month' if you would be so kind. Thank you
Roland

---------- FOLLOW-UP ----------

QUESTION: Roland, if the wire was shorted to ground along the way, shouldn't I get zero ohms at the back of the plug that goes into the dash cluster? I get different readings at this point when moving the float up and down which should change the gauge reading. I will check what you said to check, but this doesn't seem logical to me when I get different readings at the point of plugging into the gauge. Thanks!

Answer
Hi Greg,
As I explained, the dark blue wire at the tank doesn't go to the cluster gauge directly, but rather to the body computer where its signal is digitized and sent on another pair of twisted wires with other data to the cluster. So the issue is whether the varying resistance reading at the tank actually is 'seen' by the body computer or does it see 0 resistance to ground (a short in the wire to ground) which looks very much to the computer like a full tank of gas and so it tell the gauge at the cluster exactly that.
Roland
Please 'rate' my answer and consider a nomination for 'volunteer of the month". Just click on the thank/rate button.
Thank you