I'm looking to see if anyone here in the forums can shed some light on an issue I've been having with my 07 LT. If any GM techs here can speak to it that would be even better. Within the last year or so I had my fuel pump replaced under the recall notice that was sent out by GM a while back. After getting my car back everything seemed fine. Fast forward a few months and I notice my fuel gauge isn't reading properly after filling the tank. So I call the dealership up that did the fuel pump replacement and told them what was going on and said it seems like my sending unit on the new pump has an issue. They tell me to bring the car in and they would take a look at it. After "diagnosing" the issue they tell me that the problem is my gauge cluster and it needs to be replaced and reprogrammed at a cost of $700+. I told them I would get a new gauge cluster install it myself and just have them reprogram it so I could save some money. After thinking about it more though this didn't make sense to me because all of my other gauges in the cluster are functioning normally. Only the fuel gauge is effected. What is happening is the gauge doesn't immediately go to full when the tank is filled. it will stop part way, sometimes at 1/4 tank, sometimes at 3/4 or somewhere in between. Eventually it will rise to full but extremely slowly and then when the car is shut off it goes back down as its supposed to... most of the time. This morning I filled the tank and this started happening again after it had been working for about 4 days after having to jump the battery due to the car sitting over the winter and the battery dying. I thought oh ok cool the computer probably reset from the battery being dead and it's good to go now. As I am typing this though I just turned the car off and back on and it's working like it's supposed to. I'm kind of at a loss at this point and don't know if I was getting shafted by the dealership because their tech screwed up or they got a DOA part or if my gauge cluster is in fact the issue. If anyone can point me in the right direction it would be greatly appreciated.

 

The fact they want $700 for a gauge cluster install and "program" (which there is not programming, the gauge cluster just talks to the BCM) makes me warey of that dealership. You can swap out clusters, I might have a SS/NA cluster laying around I'd sell to you if you're concerned it's the cluster.

 

That was my thoughts exactly which is why i just told them i would take care of it. As for the cluster I only want to replace it if that is in fact the issue but I will keep that in mind though if that turns out to be the problem. Never thought about it before but would an SS/NA gauge work with an LT? The SS/NA gauges went to 140mph if I remember correctly but the LT only goes to 120 so would it literally just be a difference of numbers on the cluster or would everything be thrown off?

 

If it doesn't always fall to e and then goes into rest mode below e quickly when you turn it off like the speed and tac do I would suspect the fuel gauge stepper motor is going out. There is no programming or setup on our clusters. If you are feeling froggy you can ohm the sending unit, completely empty is about 40-45ohms and completely full is 240-250 ohms.
If I remember correctly the 05's are the only cluster not plug and play with other years and the rest (06-10) are swappable, (may need to double check that) the only difference you will see is color and more or less numbers on the speedo. The cluster is self calibrated internally to put the needle where the ecm says the veh speed is so nothing will be off.

 

Nice for the extra data. Also the car mileage isn't going to change (Kolt I know you know this, it's for others to prevent the question).

 

That is true on the mileage, this design cluster is one of very few gm made that the bcm and ecm store the mileage completely.

 

awesome. Thanks for the info. Not sure I will try checking the pump mainly because I dont have the proper equipment to get the tank out to get to the pump but I may just try swapping gauge clusters to see if that takes care of the issue. If that doesn't I guess that narrows it down to the pump at which point the stealership is gonna be getting another phone call from me to replace the pump again since they must have given me a defective one when it was replaced the first time.

 

You don't have to drop the tank to test the level sensor, also the sensor is separate from the pump. If you had the fuel pump special coverage done then it doesn't come with the sensor. They would have transferred the old sensor to the new pump assembly.

 

Got it. Ill take a look at that and see whats going on. Thanks for the suggestions.

 

So, not to sound like a total noob but where exactly is the fuel level sensor located? I always thought it was a part of the pump which is why I was under the impression the tank would need to be removed. Everything I am finding in google searches shows it as part of the pump.

 

it is in the tank and it attaches to the fuel pump. You can test it by disconnecting c305 and ohming the terminals there and see if your getting a good reading after you have filled up. C305 is the connector that is on the passenger side, rear of the tank, on the body.
#16 on the picture below, this view is from inside the vehicle looking down. arrow pointed toward the front.

#2 in this picture, this view is of the rear axle looking toward the front of the car.

 

Ohm between b and d terminal on the 8 way connector, female side (harness connector, not the body side mounted connector).
In the pic its the left top one, the connector in that view is with it facing you with the retention tab up.
terminals go as follows

___I---I___
| D-C-B-A |
| E-F-G-H |

 

 

awesome. thanks for all the detail and diagrams man. i appreciate it.

 

np, if you have and questions just ask. Those readings again are completely empty and completely full. In between is not gonna be accurate since you wont be able to physically see the sensor without pulling it out. Since you have a reading full issue then fill it completely full and test it, should be close to 230-250 ohms

 

will do. thanks again.