Here's a breakdown of how to test the fuel pump:
1. Listen for the Fuel Pump:
* Turn the ignition key to the "ON" position (don't start the engine). You should hear a whirring sound from the fuel tank area for a few seconds. This is the fuel pump priming the system. If you don't hear it, the pump might be faulty, or there could be a problem with the power supply.
2. Check the Fuel Pump Relay:
* Locate the fuel pump relay. The location varies slightly depending on the Tahoe's trim level and options, but it's often in the underhood fuse box. Consult your owner's manual for the exact location.
* Visually inspect the relay for any damage. Look for burnt contacts or other signs of wear.
* Swap the fuel pump relay with a known good relay of the same amperage rating (from a non-essential circuit). If the pump now primes, the original relay was bad. If not, the problem lies elsewhere.
3. Check Fuel Pump Power:
* You'll need a multimeter for this step.
* Locate the fuel pump wiring harness connector near the fuel tank. This will require getting under the vehicle.
* Disconnect the connector.
* Turn the ignition key to the "ON" position.
* Use the multimeter to check for voltage at the fuel pump connector. You should have battery voltage (around 12V) at the appropriate wires. If not, there's a problem with the wiring, fuse, or the fuel pump control module (PCM). Your owner's manual or a wiring diagram will show you which wires to test.
4. Check Fuel Pressure (Most Accurate Test):
* This requires a fuel pressure gauge. You'll need one that's compatible with the fuel system pressure of your Tahoe. This is generally the most definitive test.
* Consult a repair manual for the correct test port location and procedure. You typically connect the gauge to the fuel rail's test port.
* Turn the ignition key to the "ON" position and then start the engine. The gauge will display the fuel pressure. Compare this reading to the specifications in your repair manual. Low pressure indicates a faulty pump, clogged filter, or other issues.
Important Considerations:
* Fuel Pump Inertia Switch: Some Tahoes have an inertia switch that cuts power to the fuel pump in the event of a collision. Check to make sure this switch hasn't tripped. It's usually located in the passenger compartment, often under the dashboard.
* Fuel Filter: A clogged fuel filter can also prevent proper fuel delivery, mimicking a failing fuel pump. Replacing the fuel filter is a relatively inexpensive and easy preventative measure.
* Wiring Harness: Damage to the wiring harness between the fuel pump and the PCM can also cause issues. Inspect the harness for any signs of wear, damage, or corrosion.
If you're not comfortable performing these tests yourself, it's best to take your Tahoe to a qualified mechanic. Working with the fuel system involves potential hazards. A professional mechanic has the proper tools and knowledge to diagnose the problem accurately and safely.
