Our fuel gauge has just begun to act erratic. Our 2002 STS Cadillac reads incorrectly as it get on the low side. Then when filled up it continue to show full until turned off and turned back off it goes to correct level. What kind of cost and repair work are we talking about? Is it advantgeous to use dealer (we have always used dealer to dat) or is there another method that may be equally effective but less price intensive? Thanks so much, times are tough for us retirees!

Bad sending unit, bad ground, bad gauge, I have seen sending unit go bad they will work part way.

If the engine is cpu controlled then plugs maybe plug leads if you have them. fuel manifold pressure test, fault codes read. Remember that the cpu continually tunes the engine to suit the conditions so don't get too carried away

what could be the problem ???? The problem is you tried to fix something you have no clue how it works .... Your best bet , take it to a qualified repair shop. You have no idea of the complexity of these cadillac systems . I know you don't have a $ 5000 dollar factory scan tool or equivalent to diagnose . The sending unit in the fuel tank is a input to the BCM . The BCM sends this info to the instrument cluster over the class 2 serial data network - communication network for the control modules on the vehicle. Fuel Level
The body control module (PZM) monitors the fuel level sender input in order to determine the current fuel level. The PZM filters the input and sends a message via the Class 2 serial data line. The IPC receives this message and displays the current fuel level. The fuel level is sent from the PZM to the IPC at changes of 0.5 L (0.02 gal) or on the request of the IPC, with a resolution of 0.04 L (0.01 gal).
• For the digital IPC, when the fuel level is above 18.5 gal, the IPC displays an F. For readings between 18.5-2.5 gal, whole gallon/liter numbers are displayed. When the fuel level reaches 3.0 gal the message FUEL LEVEL LOW is displayed on the driver message center. When the fuel level reaches 2.5 gal, the IPC displays an E. When the fuel level is 1.2 gal or below the IPC displays a flashing E.
• For the analog IPC, when the fuel level is above 18.5 gal, the fuel gauge pointer is on F. When the fuel level is below 2.5 gal the fuel gauge pointer moves to E. When the fuel level is below 3.0 gal the IPC displays a FUEL LEVEL LOW message.
If the updates are not received or a communication error is detected, the IPC performs the following actions:
• For the digital IPC, the fuel gauge is dashed.
• For the analog IPC, the fuel gauge pointer moves to E.

Fuel Gage Inaccurate or Inoperative
Circuit Description
The IPC monitors the fuel level sent by the PZM through the class 2 serial data line. The IPC software controls one of the following two gauge types:
• A digital gauge consisting if a two-digit numeric seven-segment display
• An analog gauge consisting of a needle pointer.
The IPC interpolates and scales the fuel level information that the IPC receives from the PZM.
When you operate the vehicle in diagnostic mode, either in the vehicle diagnostic system or with a scan tool connected, the fuel signal supplied to the IPC is not filtered by the PZM. The unfiltered fuel signal causes the IPC to show real time readings and may be mistaken as an erratic fuel level display.
Diagnostic Aids
Connect a scan tool to the DLC.
Test for any set DTCs if no DTCs are set current. Refer to System Check in Body Control Module (PZM) Diagnosis.

Your best bet , take your vehicle to a qualified repair shop.

Yes Remove the carprt, the access is toward the front and a little to the right side. Plate held in place b 7mm screws. Thank you.

hi

this is the sensor problem which is palced in the fuel tank which senses how much fule is present inside it.
the connection to the sensor may be lose so it is not giving proper reading and erratic.

if my answer were useful please vote for me

you need a scan tool. go to auto zone they will do it @ no charge good luck.

Youre gauge is controlled by a plunger in the fuel tank which is attached to the sensor and the fuel gauge. it sounds like when the plunger goes down half way its either getting stuck down lower then it should. Needs replacing. Any mechanic can do this install for you.

alot of cars do the same thing.when the gas guage is below half, it goes down faster.

You need to remove the tank and replace the fuel pump as the sending unit is part of the pump assembly.

Why did you pull them out? I suspect that the right one did not get seated properly or there is corrosion in the connection - is the housing watertight? I don't think it's a relay since neither would work. Could be a bad ground connection on that side.