The starter relay can be elusive when diagnosing a no start situation. The battery might be blamed, the starter is another, but often the starter relay is the last item to be assessed as the problem.
The starter relay will present some very specific symptoms that you won’t find with a bad or weak battery or a starter that is going out.
Listed below are some of the distinctive symptoms of a starter relay going out:
- When the key is turned off the fuel pump runs continuously.
- Due to fuel pump running the battery is dead in the morning.
- Sudden shut-down of engine.
- Vehicle will start after a few minutes and run fine, then die again.
The starter relay should not be confused with the starting solenoid. These are two completely different components that are part of the starting system.
The action of a starter relay is interesting and, for some people, confusing. The relay works by a magnet that is energized to attract the opposing connector. The magnet attracts the connector from its position at “C” to connect with “A”. Once the connection at “A” is made the constant power from “A” can pass through to the pump. Watch the .gif below to see it in action:
If you are out and about and your vehicle suddenly shuts down it may very well be the starter relay. If you wait five minutes, or sometimes less, you may be able to start the engine again. Expect it to die again within minutes. I was able to hobble my vehicle home with this method. Starting, drive 20 feet, and it dies. Then start it again, drive another 20 feet and die again. I live in a very low population area so I was able to accomplish this. The randomness of the engine dying is too dangerous for this method in a populated area.
Another method to get you home if the starter solenoid has shut you down is to bypass it.
Bypassing the relay will get the engine running so you can drive your vehicle home but you will want to repair it properly as soon as possible.
To bypass the relay, open the hood of your car and up at the firewall, on the passenger side, you will see the starter relay attached. Locate the tan wire that is nearby. It will be coming out of the main wiring harness. It provides power to the fuel pump and a signal to the computer located in the glove compartment to let the fuel pump activate. Run a wire from the orange wire sticking out of the bottom of the starting solenoid to that tan wire that activates the pump. The orange wire is constant power and the tan wire is the fuel pump wire. Connecting them directly together will send power to the fuel pump. Thus, bypassing the solenoid. This is only a temporary solution.