Location, Diagnosis, And Replacement Of The Starter Relay In A 240sx

Alright, so you're tackling a starter relay issue on your 240SX. Good on you! It's a pretty straightforward job once you know what you're looking at. This guide will walk you through the location, diagnosis, and replacement process, giving you the confidence to get your S13 or S14 purring again. We'll assume you've got a basic understanding of automotive electrical systems and safety, but we'll keep the jargon to a minimum and explain key terms along the way.

Location of the Starter Relay

Finding the starter relay on your 240SX is the first step. Fortunately, it's typically in a pretty accessible spot.

S13 (1989-1994): For the S13 chassis, the starter relay is usually located in the driver's side kick panel area. You'll need to remove the plastic kick panel to access the fuse box and relays behind it. Look for a small, rectangular relay, often blue or black in color. The exact relay number can vary slightly depending on the year and specific model, but it's commonly identified on the fuse box diagram as the starter relay or a similar designation. The fuse box diagram is usually printed on the inside of the fuse box cover.

S14 (1995-1998): The S14 generally follows a similar layout. The starter relay is usually located in the driver's side kick panel area, behind the plastic kick panel. Again, consult the fuse box diagram (located on the inside of the fuse box cover) to positively identify the starter relay. The color of the relay may vary.

Important Note: Always refer to your car's specific service manual or fuse box diagram to confirm the exact location and function of the starter relay. There can be slight variations depending on the model year and trim level. Don't just assume it's the blue one; double-check!

Diagnosing a Faulty Starter Relay

Before you go ripping out the relay, let's make sure it's actually the culprit. There are several symptoms that can point to a bad starter relay, and it's important to rule out other potential issues first. Remember, a failing starter, a bad ignition switch, or wiring problems can mimic a faulty relay.

Common Symptoms:

• Clicking Sound: You turn the key, and all you hear is a single click from the engine bay, but the engine doesn't crank. This is a classic symptom of a relay that's trying to engage but doesn't have enough power or is internally damaged.
• No Sound at All: You turn the key, and nothing happens. No click, no crank, nada. This could indicate a completely dead relay or an issue elsewhere in the starting circuit.
• Intermittent Starting: The car starts sometimes, but not others. This can be a sign of a relay that's starting to fail and making poor electrical contact.

Diagnostic Steps:

1. Check the Battery: This is the most basic step, but it's often overlooked. Ensure your battery is fully charged and in good condition. A weak battery can prevent the relay from engaging properly. Use a voltmeter to check the battery voltage. It should read around 12.6 volts with the engine off. While cranking, it shouldn't drop below 10 volts.
2. Check the Fuses: Locate the fuse associated with the starter circuit. The fuse box diagram will identify this fuse. Use a test light or multimeter to check if the fuse is blown. If it is, replace it with a fuse of the same amperage rating. If the fuse blows again immediately, there's likely a short circuit in the starting system.
3. Listen Carefully: Have someone turn the key to the start position while you listen closely to the starter relay. Can you hear it clicking? If you hear a click, the relay is getting power and is attempting to engage. If you don't hear anything, the relay may not be receiving power.
4. The Jumper Wire Test (Caution!): This is a more advanced test and requires extreme caution. Locate the starter relay. DISCONNECT the battery! Remove the relay. Identify the two terminals on the relay socket that correspond to the switch side of the relay (usually the two smaller terminals, check your wiring diagram). Use a jumper wire to carefully bridge these two terminals. Reconnect the battery. This bypasses the relay and directly sends power to the starter solenoid. If the engine cranks, the starter relay is likely the problem. Immediately disconnect the battery after testing.

   Warning: This test bypasses safety features. Ensure the car is in neutral or park, and the parking brake is engaged. Be extremely careful not to short the jumper wire to anything else, as this could damage the electrical system.

5. Relay Swap (If Possible): If you have another relay in the fuse box that's identical to the starter relay (e.g., a horn relay), you can try swapping them to see if the problem goes away. If the problem moves to the system controlled by the swapped relay (e.g., the horn doesn't work), then the starter relay is likely the faulty one.
6. Use a Multimeter to Check the Relay: If you have a multimeter, you can perform a more thorough test of the relay. You'll need to identify the coil terminals (usually labeled 85 and 86) and the switch terminals (usually labeled 30 and 87).
   • Coil Resistance: Measure the resistance across the coil terminals. It should be a relatively low value, typically between 50 and 150 ohms. An open circuit (infinite resistance) indicates a faulty coil.
   • Continuity of the Switch: With the relay unpowered, there should be no continuity between the switch terminals. When you apply 12V to the coil terminals (observing proper polarity), you should hear the relay click, and continuity should exist between the switch terminals. If you don't hear a click or there's no continuity, the relay is faulty.

Replacing the Starter Relay

Once you've confirmed that the starter relay is indeed the problem, replacing it is a relatively simple process.

1. Disconnect the Battery: This is a crucial safety step. Always disconnect the negative battery terminal before working on any electrical components.
2. Locate the Starter Relay: As described earlier, find the starter relay in the driver's side kick panel area.
3. Remove the Old Relay: Gently pull the old relay straight out of its socket. It may be held in place by a slight friction fit.
4. Install the New Relay: Align the pins of the new relay with the corresponding slots in the socket. Push the relay firmly into place until it's fully seated.
5. Reconnect the Battery: Reconnect the negative battery terminal.
6. Test the Repair: Turn the key to the start position and verify that the engine cranks and starts normally.

Choosing a Replacement Relay:

When selecting a replacement relay, make sure to choose one that's specifically designed for automotive use and has the correct voltage and amperage rating. Use the original part number if you can find it, or cross-reference it with a reputable auto parts supplier. Using the wrong relay can damage the electrical system.

Troubleshooting After Replacement:

If the engine still doesn't start after replacing the relay, re-examine the other potential causes mentioned earlier, such as a faulty starter motor, a bad ignition switch, or wiring problems. Double-check all connections and fuses.

Final Thoughts:

Replacing the starter relay is a relatively easy task that can save you time and money compared to taking your 240SX to a mechanic. By following these steps and taking your time, you can get your car back on the road in no time. Remember to always prioritize safety and double-check your work before reconnecting the battery.