1. Verify the Sending Unit's Resistance:
* Access the Sending Unit: This usually involves dropping the fuel tank (a messy job). Consult a repair manual for your specific vehicle to determine the best access method. Safety first! Disconnect the battery negative terminal before working near fuel.
* Test the Resistance: With the sending unit disconnected from the wiring harness, use a multimeter to measure its resistance at different "fuel levels." The sending unit is a variable resistor; its resistance changes as the float moves up and down with the fuel level. You'll need a repair manual or a reliable online source (like a forum dedicated to Buick Intrigues) to find the resistance chart for your specific sending unit. If the resistance remains constant regardless of how you manually move the float arm, the sending unit is faulty.
2. Check the Wiring Harness:
* Visual Inspection: Carefully examine the wiring harness running from the sending unit to the instrument cluster. Look for any signs of damage, such as chafing, breaks, or corrosion. Pay close attention to the connector at both ends.
* Continuity Test: Use a multimeter to check for continuity between the sending unit and the instrument cluster. Again, your repair manual will show you which wires to test. If there's an open circuit (no continuity), you've located a broken wire.
3. Instrument Cluster (Less Likely):
While less likely, a faulty gauge in the instrument cluster could also cause this issue. However, since you've already established that the problem isn't a simple power or ground issue, this is lower on the list. Testing this requires specialized tools and knowledge.
4. PCM (Powertrain Control Module) - Least Likely:
The PCM receives the signal from the fuel sending unit. A very rare possibility is a faulty PCM misinterpreting the signal, but this is usually accompanied by other symptoms.
Important Considerations:
* Repair Manual: A repair manual specific to your 1999 Buick Intrigue is invaluable for this repair. It will provide detailed instructions, wiring diagrams, and resistance specifications.
* Safety: Working with fuel is dangerous. Always disconnect the battery negative terminal before starting any work near the fuel tank. Ensure proper ventilation and avoid sparks.
* Professional Help: If you're not comfortable working with automotive electrical systems or dropping the fuel tank, it's best to take your vehicle to a qualified mechanic.
By systematically checking these areas, you should be able to pinpoint the cause of the faulty fuel gauge. Remember to prioritize safety and consult your repair manual for detailed instructions.
