EPS Light came on

[idk706]

Hello to my favorite forum.
My JDM 1991 A/T RHD EPS light just came on tonight and the EPS is not working!

I was just driving earlier this evening fine, go home for an hour, hop back in the car and turn it on then the light stares me in the face.
I had already read a lot of things regarding this on the forum, took out the clock fuse and waited (realize afterwards I shouldn't have done that without grabbing the code first) that didn't work, checked battery connections, they were good.
I haven't had issues with my current battery or alternator but I really have no clue how old the battery is. It looks to be in good condition. And the charge gauge seems to always be at 14v
I had read it could also be the Main EFI relay as I have the parts but did not replace them yet. I plan on trying to retrieve a code tomorrow and then I'll replace the relay on Friday and see if that makes it go away.

Just posting to see if there is anything else I should do first or NOT do?
Cheers

 

[Old Guy]

The main EFI relay is not going to cause problems that would trigger an EPS error light.

The dash voltmeter at 14 volts would be on the low side. The 1991 service manual does not spec a voltage. The 1997 service manual infers that the voltage should be above 13.9 volts and below 15.1 volts. With a healthy electrical system most owner's report that the NSX is typically 14.5 volts to 14.7 volts. However, your reading could be due to an error in your dash voltmeter. Use a multi meter to check the voltage at the jump start terminal in the engine compartment with the engine idling. Turn on the AC with blower speed at high and headlights. If the voltage drops significantly then you may have electrical system issues that might be causing your EPS problems. However, retrieve the error codes first before doing this because some errors are not replated to the 12v system.

Your plan to drive the car again and wait until the EPS light triggers is the best plan. Take note of the driving conditions / what you were doing when the light comes on. Once the light comes on you can retrieve the error codes using the service check connector which will give you an indication of what is going on. As noted, some of those errors such as sensor errors have nothing to do with the electrical supply to the EPS.

 

[idk706]

The main EFI relay is not going to cause problems that would trigger an EPS error light.

The dash voltmeter at 14 volts would be on the low side. The 1991 service manual does not spec a voltage. The 1997 service manual infers that the voltage should be above 13.9 volts and below 15.1 volts. With a healthy electrical system most owner's report that the NSX is typically 14.5 volts to 14.7 volts. However, your reading could be due to an error in your dash voltmeter. Use a multi meter to check the voltage at the jump start terminal in the engine compartment with the engine idling. Turn on the AC with blower speed at high and headlights. If the voltage drops significantly then you may have electrical system issues that might be causing your EPS problems. However, retrieve the error codes first before doing this because some errors are not replated to the 12v system.

Your plan to drive the car again and wait until the EPS light triggers is the best plan. Take note of the driving conditions / what you were doing when the light comes on. Once the light comes on you can retrieve the error codes using the service check connector which will give you an indication of what is going on. As noted, some of those errors such as sensor errors have nothing to do with the electrical supply to the EPS.

I see. Okay I'll follow that.
When I get home from work today I'll try turning on the car today and hopefully the light will be gone.
If the EPS is still down I'd imagine it would still be mechanically safe to drive?
I'll keep this thread updated.

 

[idk706]

The main EFI relay is not going to cause problems that would trigger an EPS error light.

The dash voltmeter at 14 volts would be on the low side. The 1991 service manual does not spec a voltage. The 1997 service manual infers that the voltage should be above 13.9 volts and below 15.1 volts. With a healthy electrical system most owner's report that the NSX is typically 14.5 volts to 14.7 volts. However, your reading could be due to an error in your dash voltmeter. Use a multi meter to check the voltage at the jump start terminal in the engine compartment with the engine idling. Turn on the AC with blower speed at high and headlights. If the voltage drops significantly then you may have electrical system issues that might be causing your EPS problems. However, retrieve the error codes first before doing this because some errors are not replated to the 12v system.

Your plan to drive the car again and wait until the EPS light triggers is the best plan. Take note of the driving conditions / what you were doing when the light comes on. Once the light comes on you can retrieve the error codes using the service check connector which will give you an indication of what is going on. As noted, some of those errors such as sensor errors have nothing to do with the electrical supply to the EPS.

Afterwork today I went and shorted the connection with a paperclip and the EPS light did not turn on at all. No blinks or anything. So no code to read. I of course turned the car fully on and the EPS light was on with still no EPS active.
Now I am super unsure.
I need to go get a multimeter tomorrow and I'll test the voltage. Just wanted to update.

 

[Old Guy]

The 1991 service manual is not explicit about this; but, you have to short the service check connector then turn the ignition switch to the run position (do not start the engine) to trigger the display of the error codes.