Possible Causes & Troubleshooting Steps (in order of likelihood and ease of checking):
1. Fuel Sender Unit: This is the most common culprit. The fuel sender unit is located inside the fuel tank. It's a float that moves with the fuel level and sends a signal to the gauge. Issues include:
* Faulty float: The float could be stuck, punctured, or disconnected.
* Worn potentiometer: The potentiometer (variable resistor) within the sender unit wears down over time, leading to inaccurate readings or a completely dead gauge.
* Wiring problems within the fuel tank: Corrosion or damage to the wiring harness inside the tank can disrupt the signal.
How to check (partially): You'll need to access the sender unit (often requiring dropping the fuel tank—a significant job). Once accessible, visually inspect the float and wiring for damage. Testing the potentiometer requires specialized tools and knowledge of the sender unit's resistance values.
2. Gas Gauge Cluster: The instrument cluster itself could have a faulty gauge or a problem in the circuitry. This is less likely if the gauge is completely dead but possible if it's erratic.
* Internal failure: The gauge movement might be damaged.
* Bad connection: Loose or corroded connections inside the cluster are possibilities.
* Printed circuit board failure: A problem with the circuit board in the cluster is possible.
How to check (partially): You can try gently tapping the cluster to see if the gauge moves (a very temporary fix if it works). Diagnosing a faulty cluster usually requires specialized equipment or replacement.
3. Wiring Harness: Damaged or corroded wires between the sender unit, the cluster, and the car's computer can interrupt the signal. This is difficult to track down without a wiring diagram and a multimeter.
How to check: A visual inspection of the wiring harness is a start, but you'd ideally need a multimeter to test continuity and voltage.
4. Fuel Pump Relay or Fuse: Though less likely to cause only a gas gauge problem, a bad relay or blown fuse could disrupt power to the fuel system. Check your owner's manual for the location of these components and test them.
5. PCM (Powertrain Control Module): In very rare cases, a problem with the car's computer could interfere with the gauge readings. This is usually accompanied by other issues.
What NOT to do:
* Don't attempt fuel tank removal yourself unless you have experience. It involves working with fuel, which is extremely flammable and dangerous.
* Don't blindly replace parts. Improper diagnosis could lead to unnecessary expense and potentially damage other components.
Recommendation:
Unless you're comfortable with automotive electrical work and have the necessary tools, take your Buick Regal to a qualified mechanic. They'll have the equipment to diagnose the problem accurately and safely repair it. Replacing the fuel sender unit is a common fix, but they can test for other issues that may be contributing. Replacing the entire gauge cluster is a more costly solution, and is usually done as a last resort.
