2004 GMC Envoy Fuel Pump Fuse Location: A Direct Answer and Practical Guide
If you drive a 2004 GMC Envoy and the engine cranks but won't start, the fuel pump fuse is one of the first things you should check. The fuel pump on a 2004 GMC Envoy does not have a dedicated fuse of its own. Instead, the fuel pump relay is located in the underhood fuse block on the driver's side of the engine compartment, and the fuel pump circuit is protected by the "Powertrain Control Module B" (PCM B) fuse, which is a 20-amp mini fuse located at position #10 in the same fuse box. Several owners have reported that a blown PCM B fuse can completely shut down the fuel pump, leaving you with a no-start condition even though the engine turns over normally.
This guide will walk you through exactly where to find the fuse and relay, how to test them, and what to do if they check out fine but your fuel pump still refuses to prime.
Understanding How the Fuel Pump Gets Power
Before you start pulling fuses, it helps to understand the basic circuit. The 2004 Envoy uses a relay-controlled fuel pump system. When you turn the key to the "on" position, the Powertrain Control Module (PCM) sends a signal to the fuel pump relay, which then closes and sends battery voltage to the fuel pump. The relay gets its power from the PCM B fuse, which is why a blown fuse at position #10 can kill the fuel pump entirely without affecting the rest of the engine's ability to crank.
The fuel pump relay itself is a standard mini relay located in the underhood fuse block. According to the fuse box diagrams for the 2004 Envoy with the 4.2L L6 engine, the fuel pump relay is labeled as relay #41 in the engine compartment fuse block. This is the same fuse block that houses the PCM B fuse, so both components are within a few inches of each other.
Where to Find the Fuse Box
The main fuse block for the 2004 GMC Envoy is located under the hood on the driver's side of the engine compartment. To access it:
- Open the hood and look toward the driver's side, near the fender and the battery area.
- Press the two locking tabs on the primary cover and lift it off.
- Remove the secondary cover by snapping it off while lifting.
Once the cover is off, you will see a diagram on the underside of the cover that labels each fuse and relay. If the diagram is missing or faded, refer to the owner's manual for your specific trim level.
The Fuse and Relay You Need to Check
Here is a quick reference for the two key components:
- PCM B Fuse – Position #10. This is a 20-amp mini fuse labeled "Powertrain Control Module B". It provides power to the fuel pump relay circuit, and a blown fuse here will prevent the fuel pump from priming.
- Fuel Pump Relay – Position #41. This is a standard mini relay. It is the component that actually sends power to the fuel pump when the PCM commands it to run.
The PCM B fuse sits right next to the fuel pump relay in the fuse block, which makes checking both of them a quick and simple task.
Step-by-Step: How to Check and Test the Fuel Pump Circuit
Follow these steps in order to narrow down the cause of a fuel pump that won't prime.
1. Check the PCM B Fuse
Start with the simplest test. Pull the 20-amp PCM B fuse at position #10 and inspect it visually. A blown fuse will have a visible break in the metal strip inside the plastic housing. If the fuse looks intact, use a test light or a multimeter to verify that there is continuity across the fuse terminals.
If the fuse is blown, replace it with a new 20-amp mini fuse. Do not use a fuse with a higher amperage rating, as this could damage the electrical system and create a fire risk.
Important note: If the new fuse blows again immediately, do not keep replacing it. You have a short circuit somewhere in the system, and you need to track down the cause before you can drive the vehicle again.
2. Check the Fuel Pump Relay
If the fuse is good, the next step is to test the fuel pump relay at position #41. There are two ways to do this.
Method 1: Swap the relay. Find another relay in the same fuse block that has the same part number. The horn relay or the windshield washer relay are often good candidates. Swap the fuel pump relay with one of these others and try turning the key to the "on" position. If the fuel pump now primes, your original relay is defective.
Method 2: Test the relay with a multimeter. With the relay removed, check for battery voltage at the relay socket terminal that provides power from the fuse. With the ignition in the "on" position, you should also see voltage at the coil control terminal. If you have battery supply but no control signal from the PCM, the problem may be in the PCM or the wiring between the PCM and the relay.
3. Jump the Relay to Test the Pump
If you have confirmed that the fuse and relay are both good, you can bypass the relay entirely to test whether the fuel pump itself is working. This involves using a jumper wire to connect the two high-current terminals in the relay socket. When you do this, the fuel pump should run continuously, even with the key in the "on" position.
If the fuel pump runs when you jump the relay, then the pump is fine, and your problem lies in the control circuit. If the pump does not run when you jump the relay, then the fuel pump itself is likely dead and will need to be replaced.
Other Causes to Consider
If the fuse and relay both check out and the pump does not run when you jump the relay, there are a few other things to look at.
A Bad Ground Connection
Owners on enthusiast forums have reported a rather unusual issue with these trucks. The fuel pump relay, the left headlamp, and the left turn signal all share a common ground point at the G-107 bolt-down point on the driver's side of the engine block. If this ground connection is corroded or loose, it can cause high resistance in the ground wire, which can trip the relay and prevent the fuel pump from running.
Some owners have noticed their headlights flickering just before the engine died as a result of this problem. If you suspect this issue, locate the G-107 ground point, remove the bolt, clean the contact surfaces, apply some dielectric grease, and bolt it back down carefully.
A Damaged Fuse Box
In some rare cases, the problem is not the fuse, the relay, or the pump, but the fuse box itself. There have been reports of broken copper traces between the upper and lower sections of the underhood fuse box, which can interrupt the fuel pump circuit entirely. This is an unusual failure, but if you have checked everything else and still have no power at the relay socket, it is worth investigating.
The Fuel Pump Itself
If the pump does not run when you jump the relay, and the ground connection is good, then the fuel pump has likely failed. On the 2004 Envoy, the fuel pump is located inside the fuel tank, and replacing it requires either dropping the tank or accessing it through an access panel under the rear seat, depending on the exact model configuration.
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Final Thoughts
A 2004 GMC Envoy that cranks but won't start can be frustrating, but the fuel pump circuit is one of the easiest systems to diagnose. Start by checking the PCM B fuse at position #10 in the underhood fuse box, then move on to the fuel pump relay at position #41. Test the relay, jump it to verify the pump, and check the ground connection if needed.
If the fuel pump itself turns out to be the culprit, a high-quality replacement from KEMSO will get you back on the road without breaking the bank. Their lifetime warranty gives you peace of mind, and their affordable pricing makes them a smart choice for any DIY mechanic.
Visit https://www.kemsoracing.com/ to find the right fuel pump for your 2004 GMC Envoy today.