Honda Pilot Multi-Purpose Relay Guide (2003-2016): A/C, Fuel Pump, and More
If your Pilot's A/C quit or the engine won't start, a small, inexpensive relay is the most common culprit.
- A faulty A/C relay is the most common reason for the air conditioning to stop working on a 2003-2016 Pilot.
- This is a multi-purpose relay (OEM # 39794-SDA-A05) also used for the fuel pump, horn, and fans.
- Replacement is extremely easy, taking only minutes with no tools required, making it a perfect DIY task.
- If your engine cranks but won't start, or stalls intermittently, the fuel pump relay is a likely suspect.
The Pilot's Most Notorious Little Black Box
If you own a Honda Pilot from the 2003-2016 model years, you'll likely encounter a problem with a small, black, four-pronged relay at some point. This part, often the OEM number 39794-SDA-A05, is a known weak point, especially for the air conditioning system. The good news is that it's extremely easy and cheap to replace. 🎬 Watch: A quick fix for 2009-2015 Pilot A/C issues This article will walk you through the symptoms, how to choose the right part, and other known issues related to your Pilot's electrical system.
Symptoms of a Failing Relay
Because this is a multi-purpose relay, the symptoms will vary depending on which system it's controlling. The relay is typically found in the under-hood fuse box.
- A/C System Failure: This is the most common failure. You may experience the A/C blowing warm air because the compressor clutch is not engaging. Conversely, the relay can get stuck in the 'on' position, keeping the compressor running constantly and draining your battery overnight.
- Engine Starting Problems: When used as the fuel pump relay, a failure can prevent the engine from starting. You will hear the engine crank, but it won't fire up because it's not getting fuel. 🎬 See how to troubleshoot an intermittent crank-no-start condition You might also experience the engine stalling unexpectedly while driving or poor fuel economy.
- Overheating: If the relay for the radiator cooling fan fails, the fan won't turn on, which can cause the engine to overheat, especially in stop-and-go traffic.
- No Horn: A less critical but still noticeable symptom is the horn not working when this relay is used in that circuit.
Related Issues to Be Aware Of
Not every electrical problem is this simple relay. For 2016 Pilot models, Honda issued a Technical Service Bulletin (TSB 23-009) for an issue where the engine may not restart after an auto-idle stop. This fix may involve replacing starter relays. Additionally, a recall (NHTSA 24-010) was issued for the fuel pump motor (not the relay) on 2016 Pilots for a defect that could cause the engine to stall. If you have a 2016 model with stalling issues, check with a dealer for these campaigns.
Choosing an Aftermarket vs. OEM Relay
The original relay in your Pilot was likely made by Mitsuba or Omron. You can buy this exact part from a dealer, but it will cost more. Aftermarket relays, like the "Replacement" brand, are designed to be direct, functional copies. For a simple, plug-in part like a relay, the main difference is often price. While some mechanics are wary of aftermarket electrical parts for critical systems, the A/C relay is a very common and low-risk DIY replacement. Given the low cost and the fact that you can swap it in less than five minutes, an aftermarket relay offers excellent value.
| Part Source | Estimated Cost |
|---|---|
| New OEM (Dealer) | $25 - $40 |
| New Aftermarket | $18.08 |
| Used OEM (Salvage) | $5 - $15 |
| Shop Labor | $50 - $100 |
Pro Tip: The Swap Test
Your Pilot's fuse box has several identical relays. If you suspect your A/C relay is bad, you can swap it with a known good one, like the one for the horn. If your A/C starts working (and your horn stops), you've confirmed the relay is the problem. Just remember to buy a new relay and put the original one back in its place.
Frequently Asked Questions (FAQ)
Can I replace this relay myself?
Yes, absolutely. This is one of the easiest repairs you can do. The relay is located in the fuse box under the hood. You simply open the cover, pull the old relay straight out (you may need pliers to get a good grip), and push the new one in. The entire process takes less than 5 minutes.
Is an aftermarket relay reliable?
For this specific application, an aftermarket relay is a very popular and cost-effective choice. While OEM parts are made to the original factory standard, the high failure rate of the original A/C relay suggests that an aftermarket part is not a significant downgrade. Given the low price and ease of replacement, many owners choose the aftermarket option and even keep a spare in the glove box.
I replaced the relay but my A/C still doesn't work. What now?
While the relay is the most common cause, it's not the only one. If a new relay doesn't fix it, the next steps are to check the A/C system's refrigerant charge (it may have a leak) or check the 7.5 amp A/C fuse, which is also in the fuse box. 🎬 Watch: Locating the A/C relay and fuse on 2016 models Other possibilities include a bad A/C pressure switch or a failed compressor clutch, which are more involved repairs.
Which part number do I need?
The common OEM part number is 39794-SDA-A05. This part number has superseded older versions like 39794-SDA-A01 and 39794-SDA-A04. An aftermarket replacement will be cross-referenced to fit these OEM numbers.
Helpful Videos
Technical Specifications
OEM Part Numbers: 39794-SDA-A05 39794-SDA-A04 39794-SDA-A03 39794-SDA-A01
4-Pin Multi-Purpose Power Relay (Micro ISO)
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.
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