Here's a breakdown of how to check your fuel pump:
1. Listen for the fuel pump:
* Key On, Engine Off (KOEO): Turn the ignition key to the "ON" position (without starting the engine). You should hear a humming sound from the fuel tank area for a few seconds. This indicates the pump is priming. If you don't hear anything, the pump may be faulty or the relay is bad.
2. Check the Fuel Pump Relay:
* Locate the Relay: Consult your owner's manual or an online repair manual (like Chilton or Haynes) to find the location of the fuel pump relay. It's usually in the under-hood fuse box. The relay itself is usually a small square or rectangular component.
* Swap the Relay: Find a relay of the same amperage rating and swap it with a known good relay from a different circuit (if you have one readily available and know the function). If the problem goes away when you swap the relays, the original fuel pump relay is bad.
3. Check Fuel Pressure (Most Accurate Method, Requires Gauge):
* Safety First: This step requires a fuel pressure gauge. You'll need to carefully relieve pressure in the fuel system before disconnecting any fuel lines to prevent spraying gasoline. You can do this by turning the key ON for several seconds, then OFF. Repeat several times. Even with this, pressure might still be present, so take caution.
* Connect the Gauge: Consult a repair manual for the correct location to connect the fuel pressure gauge to the fuel rail (this usually involves a special fitting).
* Check Pressure: Turn the ignition key to the "ON" position. The gauge should register the correct fuel pressure specified in your repair manual. Low pressure indicates a potential problem with the fuel pump, fuel filter, or pressure regulator.
4. Visual Inspection (Less Reliable, But Useful):
* Access the Fuel Pump: Accessing the fuel pump typically requires dropping the fuel tank. This is a more involved procedure and may require specialized tools. Consult a repair manual for detailed instructions. Do not attempt this unless you are comfortable working on fuel systems.
* Inspect the Pump and Wiring: Once you have access, inspect the fuel pump for any physical damage, corrosion, or debris. Check the wiring harness for any broken, frayed, or corroded wires.
Important Considerations:
* Fuel Filter: A clogged fuel filter can mimic the symptoms of a failing fuel pump. Replace the fuel filter as part of the diagnostic process if you suspect a fuel pump problem.
* Professional Help: If you are not comfortable performing these checks or if you lack the necessary tools, it's best to take your Trailblazer to a qualified mechanic. Working with fuel systems is dangerous if not done properly.
Remember: Always consult your owner's manual or a repair manual specific to your 2004 Trailblazer for detailed instructions and diagrams. These instructions are general and may not perfectly match your specific vehicle. Safety should be your top priority when working on your vehicle.
