Acura RSX Relay Guide: Solving Starting and A/C Issues (2002-2006)
If your RSX won't start or the A/C is blowing warm, a faulty relay is a likely and inexpensive culprit.
- A 'crank, no-start' issue is the classic symptom of a bad PGM-FI Main Relay, a very common failure on the RSX.
- Before replacing parts, turn the key to 'ON' and listen for a 2-second hum from the fuel pump; silence points to a bad main relay.
- If your A/C is faulty or your battery dies randomly, the A/C relay is the likely cause; use the upgraded OEM part 39794-SDA-A05 for the best repair.
- Replacing a relay is a simple, plug-and-play job perfect for DIYers, with the main challenge being access to the main relay under the dash.
Is a Bad Relay Causing Your RSX Problems?
A failing relay in your 2002-2006 Acura RSX can cause frustrating and sudden issues. The most common failure is the PGM-FI Main Relay, which is notorious on this generation of Honda and Acura vehicles for causing a 'crank, no-start' condition. This happens because heat and time cause tiny cracks in the relay's internal solder joints, interrupting power to the fuel pump. Another frequent problem is a bad A/C compressor relay, which can make your A/C blow warm air or even drain your battery overnight.
Symptoms of a Failing Relay
- Car Cranks but Won't Start: This is the number one symptom of a bad PGM-FI Main Relay. The engine turns over, but it never fires up because the fuel pump isn't getting power.
- Intermittent Stalling: The engine may stall unexpectedly, especially on hot days or after the car has been running for a while. It might restart after cooling down for 20-30 minutes.
- No Fuel Pump Noise: When you turn the key to the 'ON' position (without starting), you should hear a faint 2-3 second hum from the back of the car. If you hear silence, the main relay is a prime suspect.
- A/C Blows Warm Air: If the A/C compressor isn't engaging, the relay that controls its clutch could be bad. 🎬 See how to diagnose an intermittent A/C compressor clutch failure
- Dead Battery: A faulty A/C relay can get stuck in the 'on' position, keeping the compressor clutch engaged even when the car is off and draining the battery.
Known Issue: PGM-FI Main Relay
The main relay (often blue or gray) located under the driver's dash is a well-documented weak point. Heat from the electronics causes the internal solder points to crack over time 🎬 Watch: How to test and repair your PGM-FI main relay, leading to intermittent connections. This is why the problem often appears when the cabin is hot.
Choosing the Right Aftermarket Relay
When your original relay fails, you have a few options. The OEM relays were typically made by Mitsuba or Denso. Aftermarket parts offer a cost-effective alternative.
- Premium Aftermarket (e.g., ACDelco): Brands like ACDelco are established manufacturers with a reputation for quality control. While often associated with GM vehicles, they produce reliable parts for many makes, including your RSX. This is a solid choice for a dependable repair without paying for the OEM name.
- Value Aftermarket (e.g., Replacement): This tier represents the most budget-friendly option. These parts meet basic fit and function requirements and are a good choice if minimizing cost is your top priority. Quality can be more variable than premium brands, but they provide a functional, low-cost solution.
Pro Tip: A/C Relay Upgrade
Acura released a technical service bulletin (TSB) for other models that applies to the RSX, recommending an upgraded, more robust A/C relay (part number 39794-SDA-A05). If you are replacing your A/C relay, using this specific part is a smart move to prevent future issues like a dead battery or A/C failure.
Relay Replacement Cost for Acura RSX (2002-2006)
| Part Type | Price Range |
|---|---|
| New OEM Relay | $45 - $90 |
| New Aftermarket Relay | $18 - $58 |
| Shop Labor | $50 - $120 |
Cost estimates are approximate and can vary by location and supplier.
Frequently Asked Questions
Where is the main relay located on a 2002-2006 Acura RSX?
The PGM-FI Main Relay is located under the driver's side dashboard, usually to the left of the steering column and tucked up high. You will need to remove the lower dashboard cover to access it. It is often a gray or blue box plugged into the fuse panel or a nearby bracket.
Can I replace an RSX relay myself?
Yes, this is a very DIY-friendly job. Relays in the under-hood fuse box (like the A/C relay) can be swapped in seconds. 🎬 Watch this quick guide to find your A/C relay and fuse The main relay under the dash is more difficult to reach but still just unplugs and plugs back in. No special tools are required, though a small flathead screwdriver can help release the retaining tabs. The main difficulty is the awkward position needed to work under the dash.
What is a PGM-FI relay?
PGM-FI stands for Programmed Fuel Injection. It's Honda's term for their engine management system. The PGM-FI Main Relay is the primary switch that powers up the fuel injection system, including the fuel pump and the main computer (ECM). That's why a failure of this one small part can prevent the entire car from starting.
What's the difference between the main relay and the A/C relay?
They are separate parts with different functions and locations. The main relay controls the engine's fuel system and is located under the dash. The A/C relay controls the air conditioning compressor and is typically found in the fuse box in the engine bay. A bad main relay stops the car from running, while a bad A/C relay only affects the air conditioning (or can drain the battery).
Helpful Videos
Technical Specifications
OEM Part Numbers: 39794-SDA-A05 39794-S5A-902 39794-SDA-A01
Most relays for the RSX are 4-pin or 5-pin micro ISO or standard blade-type relays operating at 12 VDC. The PGM-FI Main Relay is a larger, specialized relay assembly.
We Have This Part in Stock
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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