Safety First!
* Disconnect the battery negative terminal immediately. This prevents further drain and reduces the risk of fire. Do this before proceeding with any other steps.
Troubleshooting Steps:
1. Check the Fuel Pump Relay: This is the most common culprit. The relay might be sticking, causing the pump to remain energized even when it shouldn't be.
* Locate the relay: Consult your owner's manual or an online repair manual to find the location of the fuel pump relay. It's usually in a fuse box under the hood or inside the cabin.
* Visually inspect: Look for any obvious damage or signs of burning.
* Swap it: If possible, swap the fuel pump relay with a relay of the same amperage rating for another non-critical circuit (like the horn or wipers). If the problem moves to that other circuit, you've found the faulty relay. If the fuel pump continues running, move to the next step.
2. Check the Fuel Pump Circuit: There might be a short circuit in the wiring harness leading to the fuel pump.
* Inspect the wiring: Carefully examine the wiring harness from the relay to the fuel pump for any signs of damage, chafing, or corrosion. Look for bare wires touching each other or ground.
* Use a multimeter (if you have one): With the negative battery terminal still disconnected, you can use a multimeter to check for continuity in the fuel pump circuit. This requires some electrical knowledge and caution, so only proceed if you're comfortable doing so. Incorrect testing can lead to further damage.
3. Check the PCM (Powertrain Control Module): In rare cases, a faulty PCM can cause this problem. This is the least likely but the most expensive to fix.
* Diagnostic scan: A professional mechanic with a scan tool can check for diagnostic trouble codes (DTCs) stored in the PCM. These codes can pinpoint the exact cause.
4. Check the inertia switch: Some vehicles have an inertia switch that cuts power to the fuel pump in a crash. It's possible this is malfunctioning and stuck in the "on" position. Locate this switch (often under the dash or in the engine bay) and reset it.
5. Fuel Pump itself: While less likely to cause constant running, a faulty fuel pump could be the issue. This usually manifests as intermittent operation rather than continuous running, but it's still a possibility.
Fixing the Problem:
* Replace the relay: If a faulty relay is identified, replace it with a new one of the same amperage rating.
* Repair or replace wiring: If damaged wiring is found, repair the damage or replace the affected section of the harness. This often requires some electrical skills.
* PCM Replacement: If the PCM is faulty, it needs professional replacement and reprogramming. This is an expensive repair.
* Replace the fuel pump: If the pump itself is failing, replacement is necessary. This is a more involved repair, and usually requires dropping the fuel tank.
Recommendation:
Unless you're comfortable working with car electrical systems, it's best to take your Tahoe to a qualified mechanic. Ignoring this issue could lead to significant damage, including a potential fire. The diagnosis requires specialized tools and knowledge to pinpoint the cause safely and efficiently.
