Power Steering - EPS

[Kaz-kzukNA1]

Hi, all.

Recently, I was helping one of the owner for the Power Steering – EPS.


The owner bought this NSX knowing that the EPS was not working at all.
So, he visited my place for the Health Check service as well as to see what was wrong with the EPS.

First, I noticed that the previous owner disconnected all of the connectors going to the EPS controller. No wonder why EPS warning light was not triggered…

Also, there were many additional aftermarket wires installed around EPS controller which was worrying….

After some testing, all connectors were connected to the EPS controller and for the first time after purchasing this NSX, the EPS system was powered up and testd.
While the car was on the lift, it was fine until you hit the full lock/end stop of the steering rack. When it was on the ground, as soon as you move the steering wheel, it triggered the EPS Warning light and no more EPS…

So, time to read the EPS error code by shorting the SCS terminal. However, there was nothing stored in the backup memory…

The fun starts from here….

Quite often, on many NSX related website, there are comments such as 'if you see the warning light, reset the Controller by removing the 7.5A Clock fuse' and see whether it will fix the issue or not without reading the error code. For some of the controller, even the Workshop Manual states in the similar manner.

So, the previous owner or someone who worked on this NSX was following above procedure whenever he/she saw the EPS warning light.
Probably, the EPS failure was triggered quite often and the previous owner wanted to find a way to reset the EPS controller without pulling out the Clock fuse so many times.

So, here comes the additional wires...


I found a relay circuit on the EPS Backup power line and it was wired in a way that the EPS controller was always reset whenever the engine was stopped. No wonder why I couldn't read the error code after the EPS warning light was triggered.

However, this relay circuit was just hiding the failure and eventually, the issue got worse and worse. At the end, it looked like the owner or the person worked on this NSX gave up and decided to disable the EPS by just diconnecting all connectors from the controller.

EPS could fail for several reasons such as power relays inside the controller, the torque sensor, low battery voltage and so on.


We discussed several options and we decided to replace the power relays any way based on the initial test.
The new (in the clear bag) and old (bottom) relays. It's the standard 1a configuration however, if you are adventurous, you can get high current capacity 1a type and may be able to fit them by enlarging the through holes. I didn't check the circuit board on whether it is a multiple layers or not so be careful if you are planning to do so.
I couldn't get the specific high current one so we agreed to use exactly the same relay from the same manufacture knowing that it will fail again in distance future.
You need to be careful removing/installing the relays as it requires lots of heat due to the wide circuit pads. You will loose so much heat during the process...

So, the new relays were installed and the EPS controller was back on the NSX.

And, now we have EPS working perfectly for the first time after purchasing this particular NSX.

Another happy owner.


Regards,
Kaz