Fuel Gauge not working

Did you test before replacing ? Do you know how it work's ?

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.

fuel pressure is to low. check fuel pump.

hi,

sounds like the sending unit rheostat(sending unit) has a bad contact or break in the resistance wire. inside the tank theres a float attached to an arm that goes to a small rheostat, like a volume control on a stereo. the rheostat is sending a scratchy signal or no signal to the computer and your getting these readings. that part is inside the gas tank, the part usually comes integrated with the fuel pump. the gas tank has to be lowered to fix it.

jm

the floater is the fault which is in the fuel tank.

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.

Get manual online under $10-15 and get complete guide on whether to repair or not, service it, and how to repair etc
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The ford spec listed in the ford engine control manual is:

General Specifications Item Specification Fuel tank capacity 71.9L (19 gal) Fuel Pressure Hot restart 448-482 kPa (65-70 psi) Key ON Engine OFF (KOEO) 140-415 kPa (20-60 psi) Key ON Engine Running (KOER) 170-280 kPa (25-40 psi)

Are you measuring the fuel pressure with a mechanical gauge or are you using a scan tool . If with a mechanical gauge, does the gauge have an air purge? What symptoms does the vehicle present. If running rough you could have a fuel injector leaking. Are you measuring the fuel pressure with the key on engine off? If so, did you cycle the key a few times? Good luck

The Fuel level FLOAT, in the tank is defective. Possible that it "holed", and has sunk to the bottom of the tank.
To check, separate the harness plug to the Tank sender unit, and ground the supply to a suitable place on the frame. The dash gauge should record "Full", therefore the sender unit is suspect.
regards. DT

Hello graytape, was the fuel gauge and low fuel light working and then one day just stopped working?, if so, you have probably blown a fuse and you should be able to locate what fuse and where it's located in the owner's manual.
If you recently got the vehicle and then you found out that the gas gauge and low fuel light doesn't work then that is something completely different.
without knowing the year of the vehicle I can only give you an educated guess.
Many vehicles have a float in the gas tank and this float is directly linked to what you see on the gas gauge. However, after a number of years the floats get saturated from the fuel and become heavy, heavy enough to where they don't float anymore. That is one of the most common causes of the fuel gauge not working.
The sensor that activates the low fuel warning light may be independent of the fuel gauge and the fuel in the tank isn't low enough to turn it on. Your tank has to be very low to activate the low fuel warning light.
Good luck!

Sounds like the sending unit in the main tank is faulty.