EPS Code #25 Help

[Re<<1]

I recently took my 1998 manual NSX-T out for the first time this year and power steering was working fine, which was a shock because when I parked t in December the EPS wasn't working. After only 1 joyful day of driving with power steering the light soon appeared on day 2. I pulled the code and it is #25 .

I sent the EPS brain to BrianK last year to give it a once over after the same #25 code appeared but that didn't fix the issue.

Any idea on what to check next? Hoping I don't need to have my rack rebuilt

 

[Old Guy]

Code #25 is 'The Lower FET is Stuck On'. I am never sure what 'Lower FET' means or 'Stuck On' means, unless Lower FET means one of the two FETs on the ground side of the H bridge that drives the EPS motor. Stuck On is doubly confusing since there is nothing really to 'stick'. I supposed the FET could short circuit in the conducting position (not the normal failure mode) or perhaps something in the FET circuit is activating the FET's gate keeping it on. Anyway, not enough info in the service manual to suss out what the cryptic description means.

That said, if you get a hold of the 1997 service manual (there are links to free .pdf versions on Prime) and you check out pages 17-36 and 17-37 you will find the test procedure for dealing with code #25 (and a bunch of other codes - in this case the diagnostic does not appear to be that helpful). The diagnostic procedure is not that difficult and you might as well do it to rule out a problem with the rack (A short in the EPS motor is one of the possible causes of these error codes).

The diagnostics focus a lot on the power supply to the EPS system (flakey voltages are a known Achilles heal of the EPS. In addition to the continuity and voltage tests listed in the diagnostic, check the condition of the battery post connections, and the battery - cable connection to the body ground which can cause problems for the EPS (and other stuff). Check the ground connection for the EPS controller. Is your battery in good condition?

Edit:
I seem to recall that problems with the power relay or the fail safe relay in the EPS unit can result in error code 25. The EPS unit went through some design changes and there were relay changes. Some of the later units had marginal relay connections on the circuit board resulting in problems. Kaz has a rather lengthy discussion of the relay problem on his blog on the NSX Great Britain site. Were your relays upgraded by Brian K when he did the work on your controller?

 

[Re<<1]

Hey Old Guy thanks for the detailed information!

BrianK told me he replaced the FETs and relay. I didn't receive a parts list on exactly what was replaced though. Battery is in good condition and was left on a tinder. Never had an issue. I will check ground connections for the EPS today.

 

[Old Guy]

BrianK told me he replaced the FETs and relay. /QUOTE]

'relay'? There are two relays in the controller. The power relay which is on the +12v supply to the FET H bridge in the controller and the fail safe relay which I believe is between the negative terminal of the rack motor and the FET H bridge (its been a bit since I looked at the diagrams). Both relays carry the same amount of rack motor current and I thought that in Kaz's blog they both suffer the same problem and he replaces both. It might be worthwhile to confirm that relay is in fact both relays by emailing Brian K.

Checking the grounds is good. Do the rather simple checks in the service manual on pages 17-36 & 17-37 to diagnose a rack motor problem. Removing a rack is significant work that you don't want to do if the problem is elsewhere. My gut reaction is that if you had a #25 error, did something and the #25 went away and then reappeared, the problem is not the rack motor. Shorts or other problems in direct current motors tend to come and stay around, not go away. The tests in the service manual should confirm that.

I am of the personal opinion that leaving a battery on a tender for extended periods of time does not guarantee anything. Maintenance free batteries have a way of dying where they seem to be just fine and then 15 minutes later they are not capable of starting the car. A load test (or watch the voltage when the motor is cranking) is the only definitive way to confirm that the battery is in good condition. In April I took my NSX out of storage, reconnected the battery and my 8 year old battery started the car up just fine. However, the car was experiencing some electrical weirdness and about 1 week later the battery did the 'fine one moment dead the next moment' act. New battery and everything is just fine and the weirdness never re apeared. I am not saying your problem is battery related, just that maintenance free batteries can be deceptive.

 

[Re<<1]

Heres my update. I first checked the battery by measuring the voltage while cranking. It didn't drop below 11.5V (good battery). Then following the service manual procedure; clear DTC, start the engine and turn the steering wheel from lock-to-lock several time code #23 appeared (a problem with the circuit for check function in the EPS control unit). I then went through the trouble shooting process on pages 17-36 and 17-37. I got to the last step which states check for loose EPS control unit connectors. If necessary, substitute a known-good EPS control unit and recheck.

 

[Old Guy]

So code #25 has gone away and you now have code #23 ? Code #23 description is ominous, like the doctor doing your diagnosis has had a seizure. That almost sounds like a firmware glitch. The DTC chart lists the test procedure on 17-36 for error #23 ; but, if you read the fine print on 17-36 code #23 is not listed as one of the applicable codes for the test procedure.

I have never heard of anyone getting a code #23 . You might want to email Brian K. to see if he has any words of wisdom of check out Kaz's blog on the NSX Great Britain site. Beyond going the final step of checking for bad connections on the control unit, I have no useful advice to provide.

 

[Re<<1]

Update, After 4 weeks I finally heard back from Briank. He said "I only replace the relay that fails." Which is confusing because he initially told me "I will replace the fets and the relay." So unfortunately my next step will be to try another EPS brain to at least rule that out. Is there anyone in the central NJ area with a 97-05 that would like to meet up and go for a cruise at the same time?

 

[Old Guy]

Update, After 4 weeks I finally heard back from Briank. He said "I only replace the relay that fails." Which is confusing because he initially told me "I will replace the fets and the relay." So unfortunately my next step will be to try another EPS brain to at least rule that out. Is there anyone in the central NJ area with a 97-05 that would like to meet up and go for a cruise at the same time?

I suggest you send a PM to Kaz and ask him if he can provide any advice on the type of failures that could cause error code 23. I also note that there are two relays (power relay and fail safe relay) in the EPS controller. They both carry the same current. If only one was replaced it is possible that the other has now failed; however, I would think that would generate the more common 25 error.

 

[sylcurt]

Hi all, I am having a similar issue.

Went to start the car about a week ago to move it out of the garage , and it had not been started for about a month, and not driven all year this year. It did not start, with a dead battery for some reason , even though on a tender....never happened before...so I charged it up with a regular charger, and it started fine...no issues, drove it around the block and parked it in another shop while I did some work in the main one. I also figured that battery was about 5 years old, so I would just replace it. So, did that, and battery cable ends were a bit corroded with a slight greenish tinge, so sanded them smooth (almost like a copper look to them) and then changed the battery. So, this past weekend when I wanted to put it back into the main shop, it started real quick, (nice) but I noticed right away that the Power Steering was not working (turning wheel at slow speed was very difficult) and EPS red light in dash was on....I have never in 10+ years had an issue with EPS...and I am assuming it has something to do with the changing of the battery (car is driven very little and has low mileage for a 2000) I start it monthly year round and let run for a bit in winter, and drive it weekly normally in the summer , except for this year, as I've not driven it, as its due for some preventative service, and waiting all summer for parts to arrive for TB, WP and hose replacement...and felt that not diving it was best since its now due for this service work...(BTW, been a challenge to get all the parts needed) Anyway, I've been searching tonight on Prime and see things like resetting with clock fuse and such...and noting that there might be codes...(is this with OBDII?) do you think this is a simple reset issue, or would the control unit for the power steering just all of a sudden quit? I will remind the community that I am a lover of the NSX, and enjoy it tremendously, but not intuitively mechanical to know were things are, or how to diagnose without some direction......lets just say I am good at following directions, but with no directions, I am a bit lost mechanically....

This thread was about the best one I found pertaining to my situation also...so any suggestions on what I can do to try and pinpoint the problem? I do have a OBDII code reader...will that give me a start? And should I try the reset light thing? (clock fuse) Also, is the car still ok to drive with no EPS, or can I damage something...in case I need to drive it to the dealer to get looked at? Would there possibly be something I can re-do in changing the battery? I mean it was pretty basic, but if I unconnected everything, and reconnected it (would that possibly rectify things?) I believe I connected negative first, then positive...does that matter? Anyway, looking to try and do some self diagnosis on this...thanks all!

Curtis

 

[drew]

How to read the EPS codes
http://www.nsxcb.co.uk/showthread.php?9229-How-to-read-the-error-code

You might consider getting a manual rack and just dump your EPS. Might be a lot cheaper, easier to maintain, and the manual rack does rock.

 

[Old Guy]

The link provided by [MENTION=5430]drew[/MENTION] provides the procedure for retrieving the stored error codes using the service check connector (the OBDII does not communicate with the EPS unit for reporting error codes). This will cause the EPS light to blink if there are any stored error codes and you need to count the blinks to determine the code. There are .pdf copies of the 1997+ service manual on Prime which list the error codes.

You can try removing the clock fuse (make sure you get the correct clock fuse) and see if the problem goes away; however, make sure you retrieve the error code first since removing the clock fuse erases the code.

You can drive the car without causing damage to the EPS because it will generally shut down if it has an error. There is only one error code that allows continued operation of the EPS and I can't remember which on it is.

As to connecting the battery, the safe way to do it is connect the + terminal first and then the - terminal. That way, if the wrench touches something metallic while you are bolting the + terminal on you don't create a short. If the - terminal is already connected and you touch something metallic when bolting on the + terminal you will have an arc welding event. The connecting order will not affect things like th eEPS.

 

[Heineken]

This probably won't help much but if the EPS switches off due too low voltage (which it does when voltage goes too low during cranking, e.g.) this error is kept and the unit stays powered-off until it's reset by disconnecting and re-connecting the battery (or pulling the fuse). I experienced this when I collected my NSX and they had to jump-start it due to a weak battery. The error went away after installing a new battery and has since not returned.

In any case, the error number should be retrieved to hopefully get some more clarity about the issue.

 

[sylcurt]

I think I got it figured out (thankfully) , and my thanks once again to the NSX Prime members on the thread and especially Old Guy for your help...who PM'd me and walked me through the process in detail.

I in a nutshell, after locating the blue two wire connector (up under the dash where I tucked it when installing the footwell sub box) I shorted it out with a wire. I then turned ignition on and watched the light show in the dash....lol

I did film it with phone but from what I could tell, it was two long, two short...(22?)

Then, before doing anything else, I disconnected my battery again , and then checked clamps and such...that all seemed ok and plenty tight, but while the battery was disconnected, I took the clock fuse out, and let the whole thing sit for an hour disconnected.

I reinstalled the battery, and then reinstalled the fuse....started car, and like magic,(good magic) no lights, and EPS steering very soft and easy,,,all good! Whew!!!

FYI- I started the process of assembling parts for a complete Timing Belt job, water pump, all liquids flush and so on. I also took the liberty of deciding to get all hoses, new clamps and blots, etc listed on the Wiki here, in preparation for all this to be completed. I am now waiting on just two hoses, which are tied up in customs at the border, and I have no way at this point to get them, given the border challenges resulting from Covid. I am literally 15 minutes away from them as to where they physically are, but can't cross the border to get them , and through the summer, they were letting essential services like truckers cross, and I had a friend of a friend of a trucker pick up parts for me as they were delivered to the UPS depot at the border, and then drop it off in Canada for me...however, they have no cut truckers off from bringing personal items back across...so this is delaying me, with just two hoses left ...otherwise , I have quite an assortment. Literally every bolt , gasket, clamp, etc that would be undone will be replaced with new items once the technicians are "in there".....might be overkill, but any part that was listed n the Wiki spec sheets, I ordered...even some really tiny little screws and o rings...

It all might have to wait till spring now, as weather is getting cold, and I am two hours from Winnipeg where the work will be done.

But for now, since all seems ok, I am not going to worry about the code 22, but will have the techs do a thorough check for me when I take it in.

Thanks again Old Guy and Prime for the great help you have posted with your knowledge!