1998 Volvo S70 Fuel Pump Relay: Your Essential Guide to Diagnosis, Replacement, and Fixing a No-Start

The fuel pump relay in your 1998 Volvo S70 is a critical, yet often overlooked, component directly responsible for powering your fuel pump. When this relay fails – a common failure point in this model year – your car will crank but refuse to start due to lack of fuel delivery. Promptly diagnosing and replacing a faulty 1998 Volvo S70 fuel pump relay is the most likely solution to restore operation and avoid unnecessary fuel pump replacements or towing bills.

That clicking sound when you turn the key? Your engine cranking over strong? But no ignition, no familiar purr of the engine? If you're behind the wheel of a 1998 Volvo S70 experiencing this frustrating no-start condition, the fuel pump relay stands as the most probable culprit. This small, inexpensive electrical device acts as the gatekeeper for power to your fuel pump. When it fails, the pump gets no signal, no fuel reaches the engine, and your car simply will not start. Understanding this relay's role, knowing its location, recognizing the symptoms of failure, and knowing how to replace it are fundamental pieces of knowledge for every 1998 S70 owner. Ignoring its importance can lead to costly misdiagnoses and unnecessary repairs. This guide provides the detailed, practical information you need to tackle this common issue efficiently and effectively.

Understanding the Relay's Critical Role in Your S70's Fuel System

The fuel pump relay is not the pump itself. It is a switch controlled by electricity. Your car's Engine Control Module (ECM) sends a small electrical signal when the ignition is turned on or when the engine is cranking. This small signal isn't powerful enough to operate the fuel pump directly. The fuel pump relay acts as an intermediary. When the ECM sends its signal, the relay "clicks" closed, allowing a much larger electrical current (directly from the battery, via a fuse) to flow to the fuel pump. Without this relay functioning correctly, the ECM's command to activate the fuel pump goes unheeded. No power flows to the pump, resulting in zero fuel pressure and a non-starting engine. It’s the vital link between the car's computer command and the fuel pump's action.

Why is the 1998 S70 Fuel Pump Relay Prone to Failure?

Relays are electro-mechanical components. Inside the typical Bosch relay used in Volvos of this era (including the S70), a small electromagnet pulls contacts together to complete the high-current circuit. Over many years and countless cycles (every time you turn the key!), several things can go wrong:

  • Heat Degradation: The relay is often located in the central electronic module (CEM) behind the dashboard, an area that can get quite warm. Prolonged heat exposure gradually breaks down the internal plastic components and solder joints.
  • Contact Wear and Corrosion: The metal contacts inside the relay that physically make and break the circuit can wear down or become pitted and corroded over time. This increases electrical resistance, leading to voltage drop or complete failure to conduct electricity.
  • Solder Joint Fatigue: The solder connections attaching the relay's internal components to its external terminals can crack or fracture due to thermal cycling (heating up and cooling down repeatedly) and vibration. This is a very common failure mode specific to these Bosch relays used in 1990s Volvos like the S70. The solder becomes brittle and fails.
  • Electrical Overload/Surges: While protected by fuses, brief electrical anomalies or issues elsewhere in the fuel pump circuit could potentially stress the relay contacts.
    The 1998 model year S70 is now well over 25 years old. Age alone significantly increases the likelihood that the original fuel pump relay has reached the end of its service life or is nearing failure. Its location in a potentially warm environment accelerates this natural aging process.

Symptoms of a Faulty Fuel Pump Relay in Your 1998 S70

Recognizing the signs of a failing fuel pump relay is crucial for quick diagnosis. The primary symptoms are:

  • Cranks But Won't Start: This is the classic and most definitive symptom. The starter motor turns the engine over strongly, but the engine never catches and runs. You don't hear the brief "whirring" sound of the fuel pump priming for 1-3 seconds when you first turn the ignition key to the "ON" position (before cranking). This lack of pump prime noise is a key indicator pointing directly to the relay or its fuse/power supply.
  • Intermittent No-Start: The relay might function sometimes and fail other times. Your S70 might start fine one day, then refuse to start the next, or only start after several attempts. This inconsistency often points to failing solder joints or internal contacts within the relay. Tapping on the relay or the fuse box panel might temporarily make it work during these episodes.
  • Car Stalls Unexpectedly While Driving: Less common than a no-start, but possible. If the relay contacts momentarily lose connection while driving, it can cause the fuel pump to lose power instantly, leading to a sudden stall. Power steering and braking assist may still work initially as the engine coasts down.
  • No Spark (Potential Misdiagnosis): Sometimes, a lack of fuel (caused by the relay) can be misdiagnosed as a lack of spark. The absence of fuel prevents ignition, but spark plugs may still be firing correctly. Testing for fuel pressure or pump operation is essential.

Where is the 1998 Volvo S70 Fuel Pump Relay Located?

Finding the relay is the first practical step. In the 1998 S70 (and most P80 platform Volvos like the 850/V70/C70/S70 of that era), the central electronic module (CEM), housing crucial relays and fuses, is located under the dashboard on the driver's side.

  1. Access: You need to access the area below the steering wheel. Removing the lower dash panel (knee bolster) is usually necessary. This panel is typically held in place by several screws or clips.
  2. Location: Once the panel is off, look upwards behind the dash structure above the hood release lever and slightly to the left (towards the center console). You should see a black plastic box or module mounted to the metal dashboard support frame. This is the CEM.
  3. Identification: The CEM has a black removable cover. Carefully unclip and remove this cover. Inside, you'll see an array of relays plugged into sockets, and fuses. The relays are usually all identical Bosch-type mini relays.
  4. Finding the Right One: Identifying which relay is the fuel pump relay among several visually identical ones is critical. Here’s the essential information for the 1998 S70: You absolutely MUST consult your vehicle-specific owner's manual. It contains a detailed fuse and relay diagram identifying each socket. Look for the diagram label corresponding to the fuel pump relay – common labels include "Fuel Pump," "Main Pump," or simply an assigned number (like Relay #104). Never guess. Assuming the wrong relay will waste time and could be dangerous. If you lack the manual, search for "1998 Volvo S70 fuse/relay diagram" online – reputable Volvo enthusiast forums (like MatthewsVolvoSite or Swedespeed) or official Volvo resources are reliable sources. Don't rely on generic S70 videos or guides; model year specifics matter for relay numbering. Typically, the fuel pump relay is located in one of the rows towards the side of the CEM closest to the driver's door. Confirm with the diagram.

Step-by-Step Diagnosis: Confirming a Bad Fuel Pump Relay

Before replacing the relay, especially if it's intermittent, performing a simple diagnosis can save time and money. Safety First: Disconnect the negative terminal of your car's battery before attempting any electrical diagnosis or removal. This prevents accidental shorts.

  1. Listen for the Pump Prime: Turn the ignition key to the "ON" position (the position right before starting, where the dash lights illuminate). Listen carefully. You should hear a distinct "whirring" or "buzzing" sound coming from the rear of the car (near the fuel tank) for about 1-3 seconds. This is the fuel pump priming the system. If you hear it, the relay is working at that moment, and your no-start issue likely lies elsewhere (fuse, pump itself, ignition, etc.). If you hear nothing, proceed to step 2.
  2. The Swap Test (Easiest & Most Reliable for Intermittents): This method leverages the fact that several other critical relays in the CEM (e.g., A/C Compressor relay, Radiator Fan relay, Starter Signal relay) are usually identical to the fuel pump relay. Referencing your specific diagram, identify another relay that uses the same part number. Common swap candidates are the A/C relay or Radiator Fan Low relay. Note their positions carefully. With the ignition OFF, carefully pull out the suspected fuel pump relay and swap it with one of these known-good, identical relays. Ensure they are securely seated in their new sockets.
    • Turn Ignition ON: Listen for the pump prime sound. If you NOW hear the pump prime, the relay you just moved into the fuel pump socket is the good one, proving the one you removed from that socket is faulty.
    • Test Start: If priming sound returns, try starting the car. If it starts, further confirms the original fuel pump relay is bad.
    • If Still No Prime/No Start: Turn ignition OFF. Carefully swap the original relays back to their correct positions. This indicates the problem might not be the relay itself. Proceed to Step 3 to check for power directly.
  3. Checking for Power at the Relay Socket:
    • Relays have several terminals (usually 5). Standard relay pin functions are: 85 (Coil Ground - ECM Controlled), 86 (Coil Power - Ignition "ON" Power), 30 (High Current Power In - from Fuse), 87 (High Current Power Out - to Fuel Pump), 87a (typically unused in fuel pump applications).
    • Access: You need access to the terminals behind the relay socket in the CEM. This often requires carefully inserting multimeter probes into the back of the socket while it's still plugged into the CEM (or accessing from the wire side if possible). Use extreme caution to avoid shorting terminals. Disconnecting the battery Negative terminal is highly recommended before this step.
    • Test 1: Check for Power at Terminal 30 (Hot at All Times):
      • Set multimeter to DC Volts (20V scale).
      • Connect the multimeter's black lead to a KNOWN GOOD ground (unpainted metal on the car body).
      • Touch the multimeter's red lead to the socket terminal corresponding to pin 30 (refer to your CEM socket diagram for terminal positions).
      • You should see battery voltage (approx. 12V+) regardless of the ignition key position. If not, the main power feed from the battery (via a fuse – likely fuse #4, 25A or #13, 15A in the engine bay fuse box – check your diagram) is blown or broken. This needs fixing before proceeding.
    • Test 2: Check for Power at Terminal 86 (Ignition "ON" Power):
      • Connect multimeter as above (Black to ground).
      • Turn ignition key to "ON".
      • Touch red lead to socket terminal for pin 86.
      • You should see battery voltage (approx. 12V+). If not, there is a problem with the ignition switch or wiring supplying power to the relay coil. This needs further diagnosis.
    • Test 3: Check for ECM Ground Signal at Terminal 85:
      • This test requires extra care. Option 1: Use a test light (connect clip to Battery Positive terminal). Option 2: Use multimeter on Volts (connect Red lead to Battery Positive).
      • Turn ignition to "ON".
      • Touch the test light probe or multimeter Black lead to pin 85 socket terminal.
      • The ECM should briefly ground pin 85 (completing the coil circuit) when the key is first turned "ON" (during pump prime). You should see the test light illuminate briefly or see the multimeter voltage drop to near zero briefly. If you do not see any activation (light doesn't come on / voltage stays high) when turning ignition "ON," it suggests an issue with the ECM, its ground, or the wire from ECM to pin 85.
  4. If Power Checks Are Good: If you have power at Terminal 30 (constant), power at Terminal 86 (ignition ON), and see the ECM activate ground at Terminal 85 briefly when ignition is turned ON, but you still get no power output at Terminal 87 during that prime period (test with multimeter between Terminal 87 and ground - should see 12V briefly), then the relay itself is conclusively faulty. Even if swapping seemed to work earlier, conclusive socket power tests eliminate other circuit wiring issues as the cause of the failure when the relay is plugged in.

Buying a Replacement Fuel Pump Relay for a 1998 S70

Once diagnosed, choosing a replacement:

  1. OEM vs. Aftermarket: The original relay was almost certainly a Bosch unit. Bosch relays are known for high quality and reliability. Genuine Volvo relays (often still Bosch, branded Volvo) are a solid choice, typically offering long-term reliability. However, they are often the most expensive. High-quality aftermarket Bosch relays (with the correct Bosch part number) are functionally identical to the originals and usually cost significantly less. Avoid the absolute cheapest generic no-name relays. Reliability matters.
  2. Finding the Correct Part Number:
    • Bosch: Remove the old relay. It will have a Bosch part number printed on the top or side. Common Bosch numbers found in S70s include 0 332 014 112, 0 332 014 153, 0 332 019 373, or 0 332 005 222. Double-check the number printed on YOUR faulty relay.
    • Volvo: Volvo used its own part number system. You can cross-reference using the Bosch number above. Popular Volvo relay numbers include 944 307 and 912 686 (depending on the specific Bosch variant). Verify compatibility specifically for the 1998 S70 fuel pump location using VIN if possible.
    • Be Wary: Many retailers list relays as "fits" a wide range of models/years. While they may physically fit the socket, their internal electrical characteristics must match the original for the fuel pump load. Always match the Bosch or Volvo part number explicitly recommended for the fuel pump circuit in your specific CEM location.
  3. Best Sources:
    • Volvo Dealership Parts Counter: Most reliable, guarantees correct part, highest price.
    • Online Volvo Parts Retailers (e.g., FCP Euro, IPD, TascaParts, eeuroparts): Offer genuine Volvo and Bosch options at competitive prices. Excellent resource with accurate fitment data. Search by your VIN or specific Bosch number.
    • Major Auto Parts Stores (AutoZone, Advance Auto Parts, O'Reillys, NAPA): Usually carry Bosch relays or suitable equivalents. Be very specific about the Bosch or Volvo part number you need. Ask to see the relay and confirm the number matches your old one. Avoid generic "universal" options here.
    • Reputable General Retailers (e.g., Amazon, RockAuto): Search explicitly by the Bosch number. Check seller reviews. Confirm the relay received matches the Bosch number you ordered. RockAuto often lists multiple brand options; stick with Bosch for reliability.

Step-by-Step Replacement Process for the 1998 S70 Fuel Pump Relay

Replacing the relay itself is physically simple. Preparation and safety are key.

  1. Park Safely & Prepare: Park your S70 on a level surface, set the parking brake firmly, and place wheel chocks behind the rear wheels for maximum safety. Ensure the ignition is OFF. Disconnect the Negative (-) terminal of the battery and isolate it away from the battery post. This is crucial to prevent accidental short circuits or electrical damage while working near the fuse box.
  2. Access the CEM: Remove the lower dashboard trim panel (knee bolster) below the steering wheel on the driver's side. This usually involves removing several screws (often Torx screws, T25 size is common) and carefully unclipping plastic fasteners or clips. Be gentle to avoid breaking clips. Set the panel aside.
  3. Locate the Relay: Identify the Central Electronic Module (CEM) mounted above where the lower panel was, typically near the hood release lever towards the center console. Remove the cover if you haven't already (it usually unclips by pressing tabs). Using your specific fuse/relay diagram, visually locate the exact socket for the Fuel Pump Relay. Double-check its position against the diagram. It will look identical to several other nearby relays.
  4. Remove the Old Relay: Firmly grasp the old fuel pump relay and pull it straight out from its socket. Apply even pressure; avoid wiggling excessively which could damage the socket. Use needle-nose pliers with care if necessary, gripping the base firmly to avoid pulling only the relay body off the terminals (a sign of severe solder joint failure!).
  5. Install the New Relay: Take your new Bosch (or equivalent quality) relay. Ensure it visually matches the old one and has the correct part number. Align the terminals on the bottom of the new relay with the slots in the socket. Push the relay down firmly and evenly until it is fully seated. You should hear or feel a distinct "click" if it has locking tabs.
  6. Reassemble: Reattach the CEM cover securely. Reinstall the lower dashboard trim panel, ensuring all screws and clips are fastened correctly.
  7. Reconnect Battery & Test: Reconnect the negative battery terminal. Ensure the connection is clean and tight.
    • Ignition "ON" Test: Turn the ignition key to the "ON" position (without cranking). Listen intently for the distinct 1-3 second fuel pump priming "whirring" sound from the rear of the car.
    • Attempt to Start: If you hear the pump prime, turn the key further to start the engine. It should now crank and start normally.
  8. Confirmation: A successful start and smooth idle confirm the fuel pump relay replacement fixed the issue. If it still doesn't start and you didn't hear the prime, you must go back to the diagnostic steps in Section 4 to check socket power, indicating a problem elsewhere in the circuit. Never assume the new relay is bad without thorough testing first.

Potential Complications and What Else to Consider

While the fuel pump relay is overwhelmingly the most common cause of the symptoms described, other issues can mimic its failure or cause the replacement relay not to solve the problem:

  • Blown Fuse: The relay depends on constant power from a fuse (often Fuse #4 (25A) or #13 (15A) in the engine compartment fuse/relay box under the hood - check your S70 diagram). This fuse should be visually checked or tested with a multimeter for continuity during diagnosis. It's simple to overlook and quick to check.
  • Failing Fuel Pump: While the relay usually fails first, an internal fuel pump motor failure can present the same "crank but no start" symptom. However, the lack of pump prime sound when the relay is known to be getting power and clicking, especially after the relay is replaced and diagnosed correctly, strongly points to the pump itself being dead. Testing fuel pressure at the fuel rail (using a simple gauge) is the definitive test.
  • Wiring Harness Issues: Damage to the wiring harness connectors at the CEM, broken wires under the car near the fuel tank, or severe corrosion at the fuel pump electrical connector can interrupt power, mimicking a relay failure. This is why performing the socket voltage tests (Step 4c above) is critical after replacing the relay if the car still won't start. It confirms power is getting to the socket terminals correctly.
  • ECM Failure: A malfunctioning Engine Control Module failing to send the ground signal to the relay's pin 85 is rare but possible. This is why checking for the ECM signal (using a test light or voltmeter at terminal 85) during Step 4c is part of thorough diagnostics if socket power elsewhere is good.
  • Ignition Switch Problems: A faulty ignition switch might not be sending power to the relay's pin 86 (Ignition "ON" circuit) when the key is turned. This should be detected during the socket power test at pin 86.

Preventive Maintenance and Longevity of the New Relay

Once replaced:

  • Use Quality: The Bosch relay you installed is generally robust. High-quality replacements have a very good lifespan.
  • Location Matters: It will be subject to the same ambient heat in the footwell. While not easily modifiable, avoiding parking the car in extreme heat for extended periods might marginally help.
  • Fuse Health: Ensure the related fuse (#4 or #13 in the engine bay) is in good condition, fits tightly in its clips, and is the correct amperage. A loose or corroded fuse connection can cause problems down the line.
  • Carry a Spare: Given its critical nature, historical failure rate on these models, low cost, and ease of replacement (once you know how!), it's highly recommended for owners of older Volvos like the 1998 S70 to carry a known-good spare Bosch relay (identified and purchased in advance) in the glove compartment. This 25 part and 5 minutes of your time could prevent a major hassle, expensive tow truck call, or being stranded late at night. Especially useful for those relying on their S70 as a daily driver. Ensure you know its location and how to access the CEM quickly.

Conclusion: Mastering the Relay for S70 Reliability

The fuel pump relay in your 1998 Volvo S70 is a small component with an enormous responsibility – getting power to the fuel pump so your engine can start and run. Its failure, particularly due to solder joint fatigue in aged Bosch relays, is a well-documented, exceedingly common failure mode in these cars, leading directly to a "cranks but won't start" scenario. Armed with the knowledge provided in this guide – understanding the symptoms, knowing its exact location inside the driver's footwell CEM, being able to diagnose it using simple methods like the swap test and power checks, and knowing how to source and install a high-quality Bosch replacement – empowers you as an S70 owner. You can confidently address this issue quickly, often saving significant time, money on diagnostics or towing, and avoiding unnecessary fuel pump replacements. Remember to always consult your specific fuse and relay diagram for socket identification, invest in a Bosch relay for reliability, prioritize safety by disconnecting the battery before working on electrical components, and strongly consider keeping a spare relay readily available. Taking control of this common failure point is key to ensuring your dependable Volvo S70 continues to start reliably for many miles to come.

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