1991 Toyota Pickup Fuel Pump Relay: Location, Symptoms, Testing, and Replacement Guide

The fuel pump relay in your 1991 Toyota Pickup is a critical electrical component responsible for activating the fuel pump when you turn the ignition key. If this relay fails, your truck will crank but not start. The relay is most commonly located inside the main engine compartment fuse box, specifically identified by its green or black color and the numbering "EFI" or "Circuit Opening Relay." Identifying a faulty relay involves checking for telltale symptoms like a silent fuel pump at ignition or inconsistent starting, and verifying the issue through simple electrical testing with a multimeter or jumper wire. Replacing a bad relay with a suitable OEM or high-quality aftermarket part, such as Toyota part number 28300-16010 or equivalents from Denso or Bosch, is a generally straightforward and inexpensive repair that restores proper fuel delivery.

Understanding the Fuel Pump Relay's Role

Electric fuel pumps require power to operate. Turning the ignition key to the "ON" or "Start" position signals the need for fuel pressure. However, the fuel pump should not run continuously; it needs controlled activation. The fuel pump relay acts as the electrically operated switch that manages this critical function. Think of it as a traffic controller for power to the fuel pump.

When you turn the ignition key, the truck's Engine Control Unit (ECU) or specific ignition circuitry sends a small electrical signal to the relay coil. This signal energizes the coil inside the relay, creating a magnetic field. This magnetic field pulls down internal switch contacts. When these contacts close, they complete a high-current electrical circuit from the battery fuse to the fuel pump, supplying it with the substantial power it needs to spin and pressurize the fuel system. Once the engine starts and runs, the ECU typically keeps the relay energized, maintaining power to the pump. If the engine stalls or you turn off the ignition, the ECU de-energizes the relay coil, causing the contacts to spring back open and cutting power to the fuel pump for safety and efficiency.

Recognizing Symptoms of a Failing Fuel Pump Relay in Your 1991 Pickup

Since the relay controls power to the fuel pump, its failure directly prevents the engine from receiving fuel under pressure. The most common and definitive symptom is a cranks but won't start condition. The starter motor turns the engine strongly, but the engine doesn't fire up or even attempt to run. This happens because the fuel injectors have no pressurized fuel to spray into the cylinders. Crucially, when you turn the ignition key to "ON" (before cranking), listen carefully near the gas tank. You should hear the fuel pump whir for a brief 1-3 seconds as the system primes. A complete absence of this priming sound is a strong initial indicator of a potential relay problem, fuse issue, or pump failure.

Sometimes the relay failure is intermittent. This leads to intermittent starting problems. The truck might start perfectly fine one time, then completely fail to start the next time, or require many attempts before it finally starts. This randomness is often due to worn or corroded internal relay contacts that occasionally make or break the connection poorly. While driving, an unexpected stall or hesitation could potentially be caused by a relay momentarily cutting out, though other causes (fuel pump itself, ignition components) are more common for in-motion issues. Less frequently, a failing relay might cause visible electrical issues like flickering dashboard lights related to the EFI system when turning the key. Note that these symptoms can also point to a failed fuel pump, blown fuse, bad wiring, or ignition switch problems. Diagnosing the relay specifically is the next step.

Locating the Fuel Pump Relay in the 1991 Toyota Pickup

Finding the relay is essential for inspection, testing, or replacement. For the vast majority of 1991 Toyota Pickups (all engine variations, including the popular 22RE and V6 models, single cab or extended cab), the main fuse and relay box resides in the engine compartment, typically on the driver's side (left side for US trucks), mounted near the firewall or the inner fender well. Open the truck's hood and locate this rectangular or square black plastic box. The lid usually pulls upwards to remove. Inside the lid, or sometimes printed or embossed on the top inside edge of the box itself, you should find a fuse and relay diagram.

The fuel pump relay itself is generally green or black and is often marked with specific identifying labels. Look for text such as "EFI" (Electronic Fuel Injection) or "Circuit Opening Relay" directly on the relay housing. Checking the diagram is vital. Match the relay symbol on the diagram to its physical position within the fuse box, usually next to other important relays like the Engine Main ("ENG MAIN") relay, Headlight relay, or Horn relay. Position numbering is also common. Relay positions often have numbers like "R1," "R2," etc., or letters like "A," "B," "C." The diagram will indicate which position corresponds to the fuel pump/EFI/Circuit Opening relay. On many models, it occupies a specific numbered slot, frequently referenced as position "R3" within the engine compartment fuse box. Avoid confusing it with the similar-looking Engine Main (EFI Main) relay – check the diagram to be sure. Note: Earlier models or base trims with carburetors likely have different fuel delivery systems not reliant on this specific relay. This guide focuses on the prevalent EFI-equipped 1991 Pickups.

Testing the Fuel Pump Relay: Verify the Problem

Before replacing the relay, performing basic tests confirms whether it's truly faulty. Here are two reliable methods:

1. The "Click" and Sound Test (Simplified):

   • Turn the ignition key to "OFF." Ensure the transmission is in Park or Neutral with the parking brake firmly engaged.
   • Open the fuse box lid and locate the suspected fuel pump relay.
   • Have an assistant slowly turn the ignition key to the "ON" position (but do not crank the starter).
   • Place your fingers firmly on the relay casing. Listen and feel. A distinct, audible "click" should be heard and felt as the relay energizes when the key is turned "ON". If the truck is exceptionally quiet, you might hear the fuel pump prime for 1-3 seconds simultaneously.
   • Interpretation: If you hear and feel a definite click, the relay coil is likely receiving signal and actuating. This does not guarantee the internal power contacts are good, but it's a positive sign. If you feel and hear absolutely no click whatsoever, the relay coil circuit is faulty (possibly the relay itself, a fuse, or wiring). Lack of pump sound after a click suggests either a pump failure or the relay's internal power contacts are bad.

2. Jumper Wire Test (Bypass Test - Use Extreme Caution):

   • This test directly powers the fuel pump by bypassing the relay. Ensure the fuel system isn't leaking and you have a fire extinguisher readily available. Work in a well-ventilated area, avoid sparks or open flames. Locate the relay and identify its socket terminals. Consulting a wiring diagram specific to the 1991 Toyota Pickup is highly recommended to avoid damaging other components. Typically, the relay socket has four or five terminals:
     • Terminal 30: Constant Battery Power (Hot from battery fuse).
     • Terminal 87: Output to Fuel Pump (Power out).
     • Terminal 85: Ground for the Relay Coil.
     • Terminal 86: Switched Ignition Signal (From ECU/Ignition to trigger coil).
     • (Some relays may have an extra Terminal 87a, usually unused for fuel pump).
   • Without the relay inserted, carefully turn the ignition to "ON."
   • Using a fused jumper wire (a wire with an inline fuse holder and a 15-20A fuse is safest) or even a heavy-duty paperclip (as a last resort, carefully), briefly connect the Terminal identified as "30" (Constant Battery Power) to the Terminal identified as "87" (Output to Fuel Pump). Use the wiring diagram to be certain of terminal identity.
   • Interpretation: If the fuel pump immediately starts running loudly and continuously when you make this connection (you'll clearly hear it from the rear), it proves the fuel pump circuit from battery to pump is functional (fuse good, wiring intact, pump works). This strongly indicates the original relay is faulty. If the pump does not run during this bypass test, then the problem lies downstream in the circuit (blown fuse, broken wire, or failed fuel pump itself).

3. Multimeter Test (More Precise):

   • Continuity Test (Relay Out): Remove the relay. Set your multimeter to the continuity (beep) or Ohms setting. Measure resistance between the coil terminals (typically Terminal 85 and 86). A good relay coil should show some resistance, often between 50-150 Ohms (consult the relay specs if possible). An infinite reading (OL) indicates a broken coil - relay is bad.
   • Contact Test (Relay Out): The switch contacts (Terminal 30 and 87) should be normally open - infinite resistance (OL) when the relay is de-energized. You might need a small power source or a 9V battery to test: Apply 12V (or the voltage rating - usually 12V) across Terminals 85 (+) and 86 (-). A click should be heard, and the resistance between Terminal 30 and 87 should drop to near zero Ohms (indicating a closed switch). Remove the 12V, and the contacts should open again (infinite resistance).
   • Voltage Signal Test (Relay in Circuit): Reinstall the relay. With the ignition key turned to "ON," carefully back-probe (use T-pins or small wires without shorting adjacent terminals) the relay socket terminals using a multimeter set to Volts DC. Verify Terminal 86 has approximately battery voltage (11-12V+) when the key is "ON." Check Terminal 85 has a good ground path. If the coil gets power and ground but doesn't click or the contacts don't pass power (measure voltage at Terminal 87 when key is "ON" - should get battery voltage briefly), the relay is faulty.

Replacing the Faulty Fuel Pump Relay

Once testing confirms the relay is defective, replacement is straightforward:

1. Source the Correct Replacement: The OEM Toyota part number for the fuel pump / Circuit Opening relay on most 1991 EFI Pickups is 28300-16010 (or possibly superseded numbers like -16011/-16020 - always cross-reference your VIN with a dealer or reliable parts database). High-quality direct replacements are readily available from Denso (one of Toyota's primary suppliers), Bosch, and reputable brands like Standard Motor Products, Beck/Arnley, or Carquest Premium. Ensure the replacement relay physically matches the original (shape, terminal configuration - usually 4 or 5 pin) and shares the same specifications (coil voltage, contact amperage rating).
2. Turn Ignition Off: Ensure the key is turned "OFF" and removed.
3. Locate and Remove Old Relay: Identify the faulty relay in the engine compartment fuse box as described earlier. Relays pull straight out. Grasp the relay firmly and pull upwards vertically. There are no latches to press; it relies on friction fit within the socket pins. If stuck, wiggle gently while pulling straight up. Do not pry sideways excessively.
4. Inspect and Clean: Before inserting the new relay, inspect the terminals inside the socket. Look for any corrosion, dirt, or debris. Clean them gently using electrical contact cleaner sprayed onto a cotton swab or a small brush. Ensure no significant bends or damage exists.
5. Install New Relay: Align the terminals on the new relay correctly with the slots in the socket. The relay likely has a specific orientation. Look for keying tabs or differences in terminal sizes to guide you. Push the new relay firmly straight down into the socket until it seats completely and feels secure. Do not force it if it doesn't align; recheck the orientation.
6. Reattach Fuse Box Lid: Securely snap the plastic fuse box cover back into place.
7. Test the Repair: Turn the ignition key to the "ON" position. You should clearly hear the fuel pump prime for 1-3 seconds. Then, attempt to start the engine. If the relay was the culprit and the pump is functional, the engine should start normally.

Commonly Confused Components
Misdiagnosis is possible, so consider these:

• Fuel Pump Fuse: Located in the same engine compartment fuse box. Look for the EFI fuse (often 15-30A) or AM2 fuse. A blown fuse causes no pump operation. Always check fuses first when troubleshooting electrical problems. Visually inspect the fuse element or test it with a multimeter. Replace any blown fuse with one of identical amperage rating.
• EFI Main Relay (Engine Main Relay): Also typically in the engine fuse box, often next to the fuel pump relay. It usually powers the ECU, injectors, and sensors. A failed EFI Main Relay often results in no ECU activity – no check engine light on ignition, no injector pulse, and usually, no fuel pump prime either. They look similar; refer to the diagram.
• Ignition Switch: A failing ignition switch might not send the correct "start" or "ignition on" signals, preventing the relay from being triggered. Symptoms often include no dash lights, no crank, or intermittent loss of all functions when turning the key.
• Fuel Pump Itself: A failed fuel pump obviously won't run, even with a good relay and power. This usually requires testing fuel pressure with a gauge or confirming power directly at the pump connector.

Maintenance and Long-Term Reliability
The fuel pump relay is generally robust but can fail due to age, heat cycling, internal contact arcing, or electrical surges. Preventing future issues:

• Use Quality Replacement Parts: Stick with OEM Toyota, Denso, Bosch, or reputable aftermarket brands known for reliability.
• Protect Electrical Connections: Ensure the fuse box lid is always correctly sealed to prevent water ingress and corrosion. If you notice any corrosion on relay terminals (removed relay), gently clean them with electrical contact cleaner and a brass brush.
• Mind Aftermarket Accessories: Improperly installed high-power accessories (lights, winches, sound systems) drawing excessive current near the relay circuit or introducing voltage spikes can shorten relay life. Ensure installations are done correctly with appropriate wiring and fuses.
• Preventative Replacement (Debatable): Some owners opt to proactively replace critical relays like the fuel pump relay during major maintenance intervals on very high-mileage trucks as a cheap insurance policy, though this isn't strictly necessary if the relay tests good. Carrying a spare relay in the glove box is a practical idea for older vehicles.

Finding Parts and Estimated Costs
Replacing a 1991 Toyota Pickup fuel pump relay is one of the most cost-effective repairs:

• Toyota OEM Relay (Part # 28300-16010/16011/16020): Typically $25-$50 from dealerships or online Toyota parts specialists.
• High-Quality Aftermarket (Denso, Bosch): Generally $15-$40. Denso is often identical or equivalent to the original Toyota part. Bosch relays are also highly reliable.
• Economy Aftermarket: Available for $8-$20. While sometimes functional, longevity and reliability can be questionable compared to top-tier brands. Not recommended for critical components.
  Relays are readily available at auto parts stores (Advance Auto Parts, AutoZone, O'Reilly Auto Parts, NAPA), online retailers (RockAuto, Amazon), and Toyota dealerships. Have your truck's exact model details (engine type, VIN if possible) ready when purchasing to ensure the correct replacement.

When Relay Replacement Doesn't Fix the Problem
If replacing the relay doesn't solve your no-start or no-pump issue, further diagnostics are necessary:

1. Recheck Basics: Confirm the battery is strong. Verify the Park/Neutral safety switch is operating (try starting in Neutral if transmission allows). Double-check related fuses (EFI, AM2).
2. Test Fuel Pump Power: Using a multimeter or test light, confirm power reaches the fuel pump connector (located near the tank, often under the truck) when the key is turned "ON" or during the starter crank. Check both power and ground at the pump.
3. Measure Fuel Pressure: This is the definitive fuel system test. Rent or buy a fuel pressure gauge kit with the correct Toyota EFI adapter. Connect it to the cold start injector port or the Schrader valve (if equipped) on the fuel rail. Turn the key "ON" – pressure should build rapidly to spec (typically 38-44 psi for the 22RE engine). If pressure is low or zero, even with the relay bypassed, the pump is likely faulty or the fuel filter is severely clogged.
4. Inspect Wiring: Look for damaged, frayed, or corroded wiring between the fuse box, relay, fuel pump, and ECU ground points. Pay attention to wiring harnesses near sharp edges or heat sources.
5. Consider ECU or Ignition Circuit: Less common, but a failing ECU module could prevent sending the trigger signal to the relay. Similarly, an ignition switch failure interrupting the ignition signal path needs investigation if other symptoms point to it (dash light issues). Diagnosing these requires deeper electrical knowledge and potentially wiring diagrams.
6. Security/Gimmick Issues (Extremely Rare): Very few 1991 Pickups had rudimentary anti-theft systems. If present, a malfunction could theoretically prevent relay triggering, but this is highly unlikely compared to standard component failures.

Conclusion: A Crucial $20 Component
While small and inexpensive, the fuel pump relay plays an indispensable role in the starting and operation of your 1991 Toyota Pickup. Understanding its function, recognizing the classic symptoms of failure (cranks/no start, silent pump), knowing exactly where to find it in the engine fuse box, and performing simple verification tests (click test, bypass test) empower you to diagnose a common problem quickly. Replacement is usually a matter of minutes and minimal cost when done correctly. By focusing on this vital component using the steps outlined – from identification to testing to installation – you can often solve frustrating no-start situations and get your reliable Toyota Pickup back on the road without unnecessary expense or complexity.