1991 Chevy Silverado Fuel Pump Relay: Where It Is, How to Test It, and How to Fix It

If your 1991 Chevy Silverado cranks but won’t start, the fuel pump relay is the first thing you need to check. The fuel pump relay controls power to the fuel pump, and when it fails, the pump gets no voltage and your engine gets no fuel. On a 1991 Silverado, the fuel pump relay is located inside the cab, underneath the dashboard, directly behind the brake pedal bracket, mounted on the steering column support brace. This is different from later Silverado models, which place the relay in the underhood fuse box. If you hear no fuel pump prime when you turn the key to the ON position, the relay is the most likely culprit. The good news is that the relay is inexpensive, easy to test, and swapping it takes about ten minutes.

Understanding the 1991 Silverado Fuel Pump System

The 1991 Chevy Silverado uses a TBI (throttle body injection) fuel system. When you turn the ignition to the ON position, the Powertrain Control Module (PCM) activates the fuel pump relay. The relay then sends battery voltage to the in-tank fuel pump. The fuel pump runs for about two to three seconds to prime the system, then shuts off unless the PCM detects engine rotation (reference pulses from the ignition system). If the engine is cranking, the pump stays on. If the engine stalls, the PCM cuts power to the relay after about two seconds.

The fuel pump relay itself is a standard 5-pin ISO mini-relay. It sits inside a small relay cavity alongside other similar-looking relays near the fuse block behind the brake pedal. The relay has a coil that energizes when the PCM grounds the control circuit, and a set of contacts that carry high current to the fuel pump. When the relay fails, the symptoms are unmistakable: the engine cranks strongly but never fires, and you hear no whirring sound from the fuel tank area.

Where Exactly Is the 1991 Chevy Silverado Fuel Pump Relay?

The location is often the biggest surprise for owners who are used to newer trucks. On the 1991 Silverado, the fuel pump relay is not under the hood. It is inside the passenger compartment.

Step-by-step location:

  1. Sit in the driver’s seat and look under the dashboard, directly behind the brake pedal.
  2. You will see a metal bracket that supports the steering column. This is the steering column support brace.
  3. Mounted on that brace, you will find a small plastic relay cavity or bracket that holds several identical black relays.
  4. The fuel pump relay is one of those relays. It is usually the one with a pink and black wire going to it, or you can identify it by the wiring colors on the harness.
  5. On some 1991 models, the relay may be mounted on the passenger side firewall, behind a black plastic cover that says "Fuel Pump Relay" on it. But the most common location is behind the brake pedal bracket.

If you are unsure, the best approach is to look at the wiring diagram. The 1991 Silverado fuel pump wiring diagram shows the relay in the cabin, not in the engine compartment. The fuse block is also located under the dash, and the relay is mounted near it.

Symptoms of a Bad Fuel Pump Relay on a 1991 Silverado

A failing fuel pump relay on a 1991 Chevy Silverado produces a very specific set of symptoms. Knowing these will save you time and money.

Engine cranks but will not start. This is the number one symptom. The starter motor turns the engine over, but the engine never fires because no fuel is reaching the injectors. You might also notice that the engine tries to start briefly if there is residual fuel pressure in the lines, but then dies immediately.

No fuel pump priming sound. When you turn the key to the ON position, you should hear a soft whirring sound from the fuel tank for about two seconds. If you do not hear that sound, the relay is not sending power to the pump. Listen carefully with the windows closed, or have an assistant listen at the fuel filler cap.

Intermittent starting and stalling. Sometimes the relay works, sometimes it does not. This is a classic sign of a relay that is failing internally. The contacts may be worn or the coil may have an intermittent open circuit. The truck may start fine one day and refuse to start the next.

Loss of power while driving. If the relay fails while you are driving, the engine will suddenly lose power and stall. You will have no warning lights, and the engine will crank but not restart. This is dangerous, especially on the highway.

Check engine light on. The PCM monitors the fuel pump relay control circuit. If the relay fails, the PCM may set a diagnostic trouble code, such as P0230 (Fuel Pump Relay Control Circuit). However, on a 1991 model, the OBD-I system may not always set a code for relay failure, so do not rely on the check engine light alone.

How to Test the Fuel Pump Relay on a 1991 Silverado

Testing the fuel pump relay is straightforward and requires no special tools beyond a multimeter or a test light. You can also do a simple swap test with another relay.

Swap test (easiest method):

  1. Locate the fuel pump relay behind the brake pedal bracket.
  2. Look for another relay in the same bracket that has the same number of pins and the same shape. The A/C compressor relay or the horn relay are often identical.
  3. Pull the fuel pump relay straight out of its socket.
  4. Plug the known-good relay from the other slot into the fuel pump relay socket.
  5. Turn the key to the ON position and listen for the fuel pump prime.
  6. If the pump now works, the original relay was bad. Replace it.

Voltage test (more precise method):

  1. Turn the ignition to the OFF position and remove the fuel pump relay.
  2. Set your multimeter to DC volts (20V scale).
  3. Turn the ignition to the ON position (do not start the engine).
  4. Probe the relay socket terminals. You should see battery voltage (12V) on one of the large terminals (usually terminal 30). This is the power supply from the battery.
  5. You should also see voltage on one of the small terminals (terminal 86) when the PCM commands the relay on. This is the control circuit voltage.
  6. If you see voltage on terminal 30 but not on terminal 86, the PCM is not grounding the relay, or there is a wiring issue between the PCM and the relay.
  7. If you see voltage on both terminals but the relay does not click, the relay coil is open. Replace the relay.

Continuity test (bench test):

  1. Remove the relay and set your multimeter to ohms (resistance).
  2. Measure between terminals 85 and 86 (the coil). You should see a resistance reading between 50 and 120 ohms. If you see infinite resistance (OL), the coil is open.
  3. Measure between terminals 30 and 87 (the contacts). You should see infinite resistance (open circuit) when the relay is not energized.
  4. Apply 12V to terminal 86 and ground terminal 85. You should hear the relay click, and the resistance between terminals 30 and 87 should drop to near zero ohms. If it does not, the relay is bad.

Common Causes of Fuel Pump Relay Failure

The fuel pump relay on a 1991 Silverado is a mechanical and electrical component that wears out over time. The most common reasons for failure are:

Age and heat exposure. The relay sits in the cabin, but it still gets hot from the engine and the electrical load. After 30 years, the internal contacts oxidize, and the coil insulation degrades. This is the most common cause of failure on a vehicle this old.

Corrosion. The relay socket can develop corrosion on the terminals, especially if the truck has been driven in wet or humid conditions. Corrosion creates resistance, which heats the relay and causes it to fail prematurely.

Voltage spikes. The fuel pump is a high-current device. When it turns off, it can create a voltage spike that damages the relay contacts over time.

Vibration. The relay is mounted on the steering column support brace, which vibrates as you drive. Constant vibration can loosen the relay in its socket or cause internal wire breakage.

Other Causes of No Fuel Pump Power

If the relay tests good but the fuel pump still does not run, there are other components to check.

Fuel pump fuse. The 1991 Silverado has a fuel pump fuse in the interior fuse block. On the 1991 model, the fuse is a 20A ATO fuse labeled "F/SOL" (fuel injector solenoid) or "INJECTION." If this fuse is blown, the fuel pump will not get power even if the relay works. Check the fuse visually and with a test light.

Fuel pump itself. The in-tank fuel pump can fail after 120,000 to 200,000 miles. If the relay clicks and the fuse is good, but you still hear no pump sound, the pump motor may be dead. You can test the pump by applying 12V directly to the pump connector at the tank. If the pump runs with direct power, the wiring is the issue. If it does not run, the pump is bad.

Ground connections. The fuel pump circuit relies on a good ground path. On the 1991 Silverado, the ground for the fuel pump is typically G403, located near the fuel tank. A corroded or loose ground can cause the pump to not run, even if the relay is working. Check the ground wire for rust and clean the connection.

Wiring damage. The wiring from the relay to the fuel pump runs under the truck and can be damaged by road debris, rust, or accidents. Inspect the wiring harness for cuts, frayed wires, or melted insulation. Pay special attention to areas near the exhaust system and the rear axle.

PCM failure. In rare cases, the PCM itself fails and stops grounding the relay control circuit. This is extremely unlikely, but it can happen. Before replacing the PCM, check all wiring and connections at the PCM connector. If you have verified that the relay, fuse, pump, and wiring are all good, the PCM may be the issue.

Step-by-Step Replacement Guide for the 1991 Silverado Fuel Pump Relay

Replacing the fuel pump relay on a 1991 Chevy Silverado is a simple DIY job that takes about 15 minutes.

Tools needed:

  • New fuel pump relay (GM part number 15321059, ACDelco D1750C, or Standard Motor Products RY-601)
  • Flashlight (the area is dark under the dash)
  • Small flathead screwdriver (optional, for prying)

Procedure:

  1. Disconnect the negative battery cable. This prevents any accidental shorts or sparks while working near electrical components.
  2. Position yourself under the dashboard. You will be working behind the brake pedal, so it helps to sit in the driver's seat and lean down.
  3. Locate the relay bracket. It is mounted on the steering column support brace, directly behind the brake pedal. You may need to move the brake pedal by hand to get a good view.
  4. Identify the fuel pump relay. It is one of several identical relays in the bracket. If you are unsure, look for the wiring colors. The fuel pump relay typically has a pink wire (power from the ignition) and a dark green or black wire (control from the PCM).
  5. Pull the relay straight out of its socket. It may be tight, but it should come out with a firm pull. Do not twist it.
  6. Insert the new relay. Align the pins with the socket and push it straight in until it clicks into place.
  7. Reconnect the negative battery cable.
  8. Test the system. Turn the key to the ON position and listen for the fuel pump priming sound. You should hear a two-second whir from the fuel tank.
  9. Start the engine. If the pump primes and the engine starts, the replacement was successful.

Important note for 1991 models: The relay socket can be fragile after 30 years. If the plastic is brittle, be careful not to break the socket when pulling the relay. If the socket is damaged, you may need to replace the entire relay bracket or splice in a new socket.

Recommended Upgrade: KEMSO Fuel Pump for Your 1991 Silverado

If you have determined that the fuel pump itself is the problem, not just the relay, you need a reliable replacement. For owners of the 1991 Chevy Silverado looking for a fuel pump that delivers performance, durability, and peace of mind, we strongly recommend the KEMSO brand fuel pump.

KEMSO fuel pumps are designed as high-performance, OEM replacement units. They are built to match or exceed the original equipment specifications for your Silverado. This means you get the exact fit, the correct fuel pressure, and the proper flow rate for your TBI engine. Every KEMSO fuel pump comes with a lifetime warranty, so you only buy it once. If the pump ever fails, KEMSO stands behind it.

When you choose KEMSO, you are choosing a product that is engineered for reliability. The internal components are made from high-quality materials that resist wear, corrosion, and heat. Whether you use your Silverado for daily driving, hauling, or off-road adventures, a KEMSO fuel pump ensures that your engine gets the fuel it needs, every time you turn the key.

To browse the full selection of KEMSO fuel pumps for your 1991 Chevy Silverado and other vehicles, visit the official KEMSO store at: https://www.kemsoracing.com/

Final Thoughts on the 1991 Chevy Silverado Fuel Pump Relay

The 1991 Chevy Silverado is a classic truck, but its age means that electrical components like the fuel pump relay are prone to failure. The relay is located behind the brake pedal under the dashboard, not under the hood. If your truck cranks but will not start and you hear no fuel pump sound, the relay is the most likely cause. Testing it takes five minutes with a swap test, and replacing it costs less than $20 and takes fifteen minutes.

If the relay is good but the pump still does not run, check the fuse, the wiring, and the ground connections before replacing the pump. And if the pump itself is bad, choose a KEMSO fuel pump for a reliable, long-lasting solution backed by a lifetime warranty.

For more information on KEMSO products and to find the right fuel pump for your 1991 Chevy Silverado, visit https://www.kemsoracing.com/ today.


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