Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

2002 Pontiac Montana fuel gauge

The fuel gauge on the Montana was getting erratic, jumping up and down and now it’s stuck on full the whole time. I disconnected the connectors under the second row seats to see if the sending unit was at fault. The gauge is still stuck on full. Turning the car off, the gauge goes down to empty like it should. Apparently the sending unit is not at fault since disconnecting it didn’t affect the gauge. I was playing around with the wiring harness running along the driver’s side seat and got the gauge to move every once in a while. Any clues as to where the problem might be? Looks like whatever the problem is, it’s telling the gauge that there is a full tank of gas, even without the sending unit hooked up.

Actually, There Is A Possible Clue.

2000-2005 Montanas are amongst a list of 2002 through 2007 GM vehicles in a GM Technical Service Bulletin that identifies some electrical problems. If you’ve got one or more of a list of electrical issues, which can be intermittent or not, there is a place on the vehicle to check. “Fuel gauge is inoperative or fluctuates” is one of them.

I’m ot sure which connectors you disconnected, but the C305 connector (probably in that harness you were jiggling) on the floor to the rear of the driver’s seat is not sealed and some have been found to corrode because of moisture. The connector’s terminals need to be inspected and some may require replacement. The source of the water must be found. The bulletin is # 01-08-45-005E.


Thanks for the information on the TSB. The connector I disconnected was the one directly under the second row driver’s side seat, underneath the vehicle. I believe there were 2 multipin pin connectors and 1 single connector, not quite sure. When I disconnected them and started the engine, it ran for a few seconds and then died. I guess I disconnected the fuel pump. I haven’t followed the wiring harness to see where it comes into the passenger compartment but I did notice that the driver’s side carpet and mat were absolutely soaked, possibly from rain, not air conditioning. I don’t understand why the gauge still reads full after disconnecting the harness from the sending unit unless the sending unit is not part of that harness.