Help - Troubleshooting EPS - code 25, open lower FET

Hello,

I am trying to troubleshoot a 1998 Acura NSX-T with the Power steering / EPS not working correctly. I flashed the service connector and received 2 long and 5 quick flashes. Per the 97-2005 service manual, it corresponds or indicates it is a code 25 (open lower FET or is stuck on). If I pull the clock fuse and re-set the ECU, the EPS light will shut off and power steering will work then it will immediately turn off and the light will stay on.

Any recommendations on how to fix this would be most appreciated. Thanks so much!

This is going from educated assumptions rather than direct experience, so take with a grain of salt.

FET is the abbreviation for Field Effect Transistor. If you look at the middle of page 17-19 of the service manual, you will see something called current sensor. Around the current sensor are 4 identical looking 'things'. Those 4 things are FETs, likely power MOSFETS that are configured in something called an H bridge and provide bi directional current control of the motor in the rack. I am going to guess that the 'lower FET' referred to in error code 25 are the FETs on the lower half of the H bridge. There is a diagnostic procedure on page 17-36 of the service manual that you should go through to help you determine the nature of the problem. Hopefully, it is not a shorted or open circuit in the motor in the rack.

If the rack motor tests out good, Kaz has posted discussion of problems with the EPS controller. Specifically, there are one or two relays in the controller that fail causing error codes. His posts talk about replacing the relays with higher rated or different relays which are more immune to failure. I can't remember for sure; but, the problematic relays may be the power relay and / or the fail safe relay that are connected to the H bridge in the motor circuit (page 17-19). A failure of the fail safe relay could look like an open circuit in the rack motor which is one of the things that the manual says can trigger error code 25. Rather than me trying to repeat Kaz's discussion, do a search on EPS control unit problems. You should be able to find the link. The actual discussion is posted on his forum in Britain.

You could also try contacting Brian K at NSX Erepair. He may or may not do the repairs on the EPS controller. If he does, he may be able to advise whether code 25 is one of the codes triggered by the relay failure. But, definitely do the diagnostic in the service manual to rule out a problem with the motor in the rack.

Old Guy said:

if you look at the middle of page 17-19 of the service manual, you will see something called current sensor....There is a diagnostic procedure on page 17-36 of the service manual that you should go through to help you determine the nature of the problem

Click to expand...

thanks so much for taking the time to reply. what year manual did you pull this info from? reading my 97-2000 manual, I did not find a 17-36 and the 17-19 I found is only a 17-19f where it talks about the Manual Steering Gearbox Removal/Installation.

My car is a 2000, so I have the original 1400+ page Acura black paper service manual for 1997 along with the supplemental service manual to cover changes for the 2000 model year. The 2000 supplement only has 2 pages covering some comments on the self diagnostics for the EPS (the 25 error code remains the same) and refers back to the 1997 service manual for everything else with respect to the EPS. So, the 1997 service manual should also apply to your 1998 for the EPS.

You make reference to the 97-2000 manual. If you are using the .pdf version of the manual which is called the 1997-20005 manual, there are a whole bunch of pages that never got entered into that document. The DTCs for the EPS are listed on page 17-25 which refers to page 17-36 for the test procedure; but, there is no 17-36 scanned in the .pdf version. There are other pages missing. It also appears that the circuit diagram which was on 17-18 and 17-19 may not exist in that version of the manual. If you look at page 17-14 of the .pdf document, there is a rather poor diagram in the center of the page which gives a general idea of the arrangement of the H bridge and power and fail safe relays.