A Guide to Relays for the 2004-2008 Scion xB
Understand the small electrical switches that can cause big problems like a no-start condition or overheating in your first-generation Scion xB.
- Relay failure can cause a no-start condition, overheating, or a dead battery.
- Many relays are multi-purpose; you can swap them to diagnose a problem.
- Denso is the OEM supplier; buying a Denso-branded relay is a reliable choice.
- Replacing a relay is a very simple DIY task that requires no tools.
Understanding Relay Failure in Your Scion xB
The first-generation Scion xB is a reliable vehicle, but like any car, its electrical components can wear out. Relays are simple devices, but they are essential for your car to work correctly. When a relay fails, the component it controls may stop working altogether, work intermittently, or get stuck in the "on" position. Because many relays in your xB are identical, a common diagnostic trick is to swap a suspect relay with a known good one from a non-essential system (like the horn) to see if the problem moves.
Common Electrical Gremlins
Owners of the 2004-2008 Scion xB often report electrical issues that can be traced back to a failing relay. These can include the car not starting, the engine overheating, or accessories not working. While there are no official recalls for relays on this vehicle, these problems are frequently discussed in owner forums.
Choosing the Right Aftermarket Relay
When a relay fails, you have a choice between an Original Equipment Manufacturer (OEM) part and an aftermarket part. For the Scion xB, the original relays were made by Denso.
- OEM (Denso): These are the same parts your vehicle was built with. Denso is a well-respected brand known for quality and reliability. You can buy a Denso-branded relay from an auto parts store, which is often identical to the one from a Toyota/Scion dealership but may cost less.
- Aftermarket (Replacement): Aftermarket brands like Standard Motor Products (SMP) or other store brands offer a more budget-friendly option. For a simple component like a relay, a quality aftermarket part is often a perfectly acceptable and cost-effective choice. Many of these relays are multi-purpose and can be used in different locations in your xB.
Pro Tip: Many relays in the fuse box are the same part number. If you suspect your fuel pump relay is bad, for example, you can swap it with the horn relay to test. If the car starts and the horn stops working, you've found your problem. Just be sure to replace the bad relay promptly.
Installation Overview
Replacing a relay is one of the easiest repairs you can do. The main relays are located in the fuse box in the engine compartment, on the driver's side. Simply open the fuse box, identify the correct relay using the diagram on the lid, and pull the old relay straight out. Then, push the new relay firmly into the socket. No tools are typically required.
| Part Type | Price Range |
|---|---|
| New OEM (Dealership) | $40 - $80 |
| New Aftermarket (Denso, SMP, etc.) | $18 - $35 |
| Shop Labor for Diagnosis & Replacement | $50 - $150 |
Frequently Asked Questions
Where are the relays located on my 2004-2008 Scion xB?
The primary relays for components like the fuel pump, cooling fan, and starter are located in the main fuse and relay box in the engine compartment. This box is typically a black plastic case found near the battery on the driver's side. There is also an interior fuse panel under the dashboard on the driver's side that contains some fuses and smaller relays.
My xB won't start, but the battery is good. Could it be a relay?
Yes, a "no-crank, no-start" issue is a classic symptom of a failed starter relay. When you turn the key, the starter relay is supposed to send a large amount of power to the starter motor. If the relay is bad, you might hear a single click or nothing at all. The fuel pump relay (often called the C/OPN or Circuit Opening relay) can also prevent the car from starting, though the engine will typically crank but not fire up.
My cooling fan is always on, or it never turns on. Is that a relay problem?
It very well could be. A cooling fan that runs constantly, even when the car is off, can be caused by a relay that is stuck in the "on" position, which can drain your battery. A fan that never turns on, causing the engine to overheat in traffic, can be due to a failed relay that won't switch on. Owners have sometimes bypassed failed relays as a temporary fix, which can cause the fan to run constantly.
Are all the relays in the fuse box the same?
Not all, but many of them are. The 2004-2008 Scion xB uses a common multi-purpose relay for several different functions, such as the horn, headlights, and fan motor. This is why swapping them for diagnosis is possible. However, there are also specific relays, like the larger starter relay or integrated relays, that are not interchangeable. Always check the part numbers when replacing.
Helpful Videos
Technical Specifications
OEM Part Numbers: 90987-02027 90080-87026 90987-04004 28300-10020
Most common relays are 4-pin, 12V DC, single-pole single-throw (SPST) multi-purpose relays. They are located in the engine bay and interior fuse panels.
The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.
- Scion xB: