* Fuel Level Sender Unit: This is the most common culprit. Located in the fuel tank, the sender unit is a float that moves with the fuel level and sends a signal to the gauge. Problems include:
* Faulty float: The float could be broken, stuck, or leaking.
* Worn or corroded contacts: The electrical contacts within the sender unit can corrode or wear down, preventing a reliable connection.
* Wiring issues within the sender unit: Internal wiring can break or become disconnected.
* Sender unit itself is bad: The whole unit might need replacing.
* Wiring: Issues with the wiring between the fuel level sender and the instrument cluster are another frequent cause. This includes:
* Broken or frayed wires: Look for cuts, chafing, or corrosion in the wiring harness.
* Loose connections: Connectors may be loose or corroded.
* Short circuits: A short in the wiring could cause the gauge to malfunction.
* Instrument Cluster: The gauge itself could be faulty:
* Burnt-out bulb (if it's just a blank space): This is less likely if the gauge is showing something other than empty (it will be pegged at full or empty if it's burned out).
* Internal failure of the gauge mechanism: The gauge itself could have failed.
* Fuel Pump Relay (Less likely): While less likely to directly cause a fuel gauge failure, a failing fuel pump relay *could* sometimes affect the signal to the sender.
* Grounding Issues: A poor ground connection anywhere in the circuit can cause erratic readings or a complete failure.
Troubleshooting Steps:
1. Check the fuel level (duh!): Sounds obvious, but make sure the tank isn't actually empty.
2. Inspect the wiring: Carefully examine the wiring harness connecting the fuel tank to the instrument cluster for any damage or loose connections. Pay close attention to the area near the fuel tank where it's more prone to wear.
3. Test the fuel level sender unit: This requires a multimeter to check the resistance across the sender unit's terminals. You'll need a repair manual or online resources to find the correct resistance values for your specific Blazer model. Testing requires dropping the fuel tank or accessing the sender from underneath the vehicle.
4. Check the fuses: Inspect the fuses related to the instrument cluster and fuel system.
5. Check the instrument cluster: This requires more advanced diagnostic tools or replacing the cluster (a last resort).
Important Note: Working on the fuel system can be dangerous. Disconnect the battery negative terminal before working on any electrical components related to the fuel system. If you're not comfortable performing these checks yourself, take your Blazer to a qualified mechanic. They have the tools and experience to diagnose and repair the issue safely and efficiently.
