NSX Health Check Service

[Kaz-kzukNA1]

Back to the Yellow Targa NSX....

4. Main Relay

All of the owners who took my Main Relay service will have their original parts re-soldered so that it can be used for emergency spare for other owners.

I received several requests regarding how to replace the Main Relay so would like to share this info with you.
When the Main Relay fails, you can still crank the engine with the starter but there will be neither fuel nor spark and thus, the engine won’t fire up.

Depending on whether your NSX is equipped with DBW or not, the location of the Main Relay is different. Don’t worry even if you don’t understand the word ‘Drive By Wire – DBW’ model. The first interior panel that you need to remove is the same for both DBW and Non-DBW model.


[Edit: Parts No. Info.]
39400-SL0-003: For non-DBW model
39400-SL0-A01: For DBW model



The Main Relays for DBW and Non-DBW model. Although the number on the case is different (0101 vs 0152), the internal circuit board and the parts are the same. The bracket is different between the two. Also, on the relay inside, you can see the Year number on it. The internal relay was upgraded during early 90’s. Originally, it had coiled spring inside the relay module but later it was replaced with the spring plate.


When you sit on the right side seat, the Main Relay on Non-DBW model is located just behind your Left shoulder. For DBW model, it is behind your Right shoulder and thus, you will need to remove extra interior panel.


First, you need to remove the Rear Upper Trim. There are three clips at the top and one sharp needle like pin located at the left top side of the trim. There are several metal hooks at the bottom. Using both hands, first push down the top side of the trim and then pull it gently towards your body and lift it up to release the hook. The upper trim will come off.


Now look for a small black box behind the left shoulder of the right side seat with the label as ‘RELAY ASSY, MAIN RZ-0101’ on it.
It is next to the big silver box (EFI ECU).

If you can’t find it, your NSX is DBW model and requires extra panel to be removed.

If you found the Main Relay, you can replace it with new one by removing just one fixing bolt on the bracket and two connectors at the bottom. You may struggle to access the connectors but if you remove the fixing bolt, it will provide you with extra space allowing you to access the connectors.