EPS problems

[Midnight Blue]

Hi,

I have a 1995 NA1 auto Targa. The EPS light has been coming on if I put in any large steering input just after starting.
If I clear the fault code, (41) and set off in a straight line it will run fine thereafter. It is gradually getting worse though and so I need to fix it.

The 1991 service manual gives fault cde 41 as the EPS controller and shows it in a rack behind the glove box. Unfortunately my car is a 1995 and there is nothing there.
I know that the EPS power supply box in the passenger footwell was changed for the 1995 models.

Question 1) Are the functions of the EPS controller now in the EPS power supply unit or is there another box somewhere?

Question 2) What does fault code 41 mean on a 95 car, is it still EPS controller?

There was a suggestion that it may be the battery dying, which is no surprise here as they only last 2-3 years in this climate, so I changed it for a new one but that didn't help.

Regards,

Andy

[NSA]

My 1997 NSX has the EPS controller behind the speaker in the passenger footwell. You have to pull back the carpet and remove the speaker to get to it. This is fairly easy to do.

I had a similar problem and have now have a spare EPS controller for sale.

[Midnight Blue]

In pre 1995 cars the box in the footwell was only a power supply unit, the controller was elsewhere.

What fault code did you have prior to repair? Is this papa'a old box repaired by BBA-reman?

Does anyone have any wiring diagrams, test schedules etc for the EPS controler?

regards,

Andy

[Kaz-kzukNA1]

Hi, Andy.
As your car is ’95 NSX-T (which was first introduced in Jan/95), it will be NA1-130.
So, the answer for your original questions based on your model number is;

Q1: From NA1-130, the EPS controller (EPS unit) was located at the passenger footwell. It combined the system and power control in one box. Up to and including NA1-120 with EPS equipped, the controller was positioned in the rack behind the glove box (as in your post) and the power module was at the passenger footwell.

Q2: Yes, it is still the same but as you can see in the manual, it only tells you to use a new controller to see whether it will fix the issue or not. It doesn’t help a lot….

For your reference, followings are some of the information that I would like to share.

1. EPS controller (part no.: 39980-SL0-033)
As your car is NA1-130, this is very unlikely to be the case but in case you were not aware of …
There was a Technical Bulletin from Honda regarding the EPS controller issue with specific chassis no. region.
It was for the ’97 model with EPS controller part no. 39980-SL0-033. After this issue, all of the NA1-140, NA2-100 cars and onwards were fitted with 39980-SL0-043 or later version (I think it is now up to -073 or something).
I don’t know whether the parts no. is written on the EPS controller box or not but your car was equipped with 39980-SL0-023 when it left the factory. I hope no one replaced it with -033 version.

2. Testing EPS controller
Even with the wiring diagram and test schedule, it will be very difficult to bench test the EPS controller without the proper simulator. You need to know the torque figure from the steering rack, the car speed from your main speed sensor and the one from your AT controller and the output current to the motor inside the steering rack. There was also steering angle/speed sensor used for the input information. I know it was removed at some point (possibly from NA1-140&NA2 models) but I cant' remember. In summary, you can't test it without the proper simulator as you need to know the simulated input, calculated output and measured feedback output.

In fact, the failure code suggesting the EPS controller issue tends to be triggered by the combination of controller and/or the steering gbox issue. Baically, you can't tell whether the EPS failure was triggered by the input or the output.

Common issue is the torque sensor failure inside the steering gbox. From your failure code, it seems that you are the lucky one not to have this failure. At this stage, there are no spare parts just for the torque sensor so you have to replace the entire steering gbox which will be very-very expensive.

Several people noticed similar EPS failure code when they replaced their wheel/tyre/alignment using quite different size/setup compared to the original spec. Later model seems to have better tolerance against these factors so something to be considered. Are you using any different setup?

I heard some people managed to trigger the EPS failure on leaving a specific parking bay. I don’t know the detail but I heard it was one of those electronics parking tower popular in Japan. The car will be parked on a small platform/bay and it will be stored away by the lift inside the building to utilise the small land space efficiently. When the car was about to leave this bay, the front wheel is on the rigid ground whereas the rear end is still on the wobbly bay which could generate unusual torque input to the front at very-very low speed.

It doesn’t trigger the EPS failure but I know some of the NSX with EPS can get notched/stepped feeling when you apply small amount of torque on the steering wheel. It’s like the assist motor is trying to switch itself on/off/on very frequently. This can be caused by the black oxidised residue at the rotor commutators where the brush is sitting on. If you used your EPS for long years and know someone who can disassemble this steering gbox, it would be a very good idea to give a good cleaning as well as re-grease the rack.

Also, the steering rack at the passenger side tends to show some play after long years. This is caused by the worn out bush which holds the rack inside the gbox. Again, these is no spare parts just for this internal bush.

So, not much help but wanted to share some information as your failure code could be related to outside of the controller unit. The control of EPS from your model has changed quite a lot compared to the original ones. It provides you with more smooth feeling against the car speed. Because of this improved control, I do hope your controller is fine.

Regards,
Kaz

[Midnight Blue]

Kaz,

Thanks for the detailed reply.

My chassis number stats JHMNA128 and is a 1995 model Targa Auto.

The wheel and tyre's are standard size.

I have had the car lifted and there appears to be no binding or restriction on steering travel from lock to lock. The EPS would work correctly with the car raised and with the car partially supported and it only tripped off when the full weight of the car was on the wheels. This would suggest that it is a current overload trip.

I have removed the EPS controller, (just the one alloy box in the footwell) and given it to the new member here in Brunei Snowman01 to check out, he is much more comfortable dealing with wiggly amps than I am as it is his specialist subject.
If I recall correctly the part number was -023. He cannot do too much without any test sequences but will check for dry joints, leaking capacitors and pitted relays. I think he is favouring the relays as being the likely culprit.

Regards,

Andy

[snowman01]

Hi Andy,
Your EPS box is indeed a 39980-SLO-023, nice little slogan on case "AN ETERNAL SPORTSMIND FOR YOU", well maybe not eternal if it has given up the ghost! Now about to dismantle and inspect relays, will keep you informed.
Regards
Karl

Update - EPS Box dismantled see pics.

[Kaz-kzukNA1]

Hi, Karl.
Nice photos.
The power relay ACB33101 is only rated at 40A.....
Quite surprised considering the total current going through the FETs.
The first time when I saw this massive current flow box was the 4WS (four wheel steer) system on Honda Prelude.
As ususal, entire case has been used as the heatsink.

Hope the rest of the board is fine as I do like the improved control of EPS from '95 onwards.

Thank you.

Regards,
Kaz

[snowman01]

After some time sourcing new items I have fixed the problem components. Not adviseable to attemt repair if you have not had a lot of experience at soldering. The damm components just do not want to de-solder. The board has been lacquered after soldering at manufacture!

[Papalazarou]

I love the hidden message in post 6, picture 2.


Cheers,


James.

[Midnight Blue]

James,

Not in my car they didn't! Sounds just like a typical conversation out here in Brunei. To make a statement a question you add "A?"

James, thanks for the advise you gave me a couple of months ago when the problem first started.

No problems now with the EPS since Mr Snowman fixed it by replacing and uprating the components. (Thanks Karl). The only problem is that the wife may actually want to drive it now.

Cheers,

Andy

[Papalazarou]

Good, glad it worked out. Having no pas is a real pain.


Cheers,


James.

[NSXGB]

Good, glad it worked out. Having no pas is a real pain.


Cheers,


James.


.....I've never found it a problem....:)
Sounds like it's more trouble than it's worth. ;)

[Midnight Blue]

quote.....I've never found it a problem....:)
Sounds like it's more trouble than it's worth.

Hi,

If I have got it right, the rack used on EPS equiped cars is quicker than the standard racks (and the same ratio as the NSX-R) and is unpleasantly heavy for parking. More so than the unassisted cars.

The EPS has faded out completely by about 25mph and after that it is just a nice unassisted quick rack.

Cheers,

Andy

[NSXGB]

Hi,

If I have got it right, the rack used on EPS equiped cars is quicker than the standard racks (and the same ratio as the NSX-R) and is unpleasantly heavy for parking. More so than the unassisted cars.

The EPS has faded out completely by about 25mph and after that it is just a nice unassisted quick rack.

Cheers,

Andy

Not a lot in it but if your car is an auto it is the same as an early non PAS manual.

'91-'94 5-speed cars have an 18.6:1 ratio
'95+ manual cars have a variable ratio of 18.2:1 to 20.8:1.
All automatics to date have EPS with an 18.6:1 ratio regardless of year.

(From NSX Prime Wiki).

[Papalazarou]

Ok, that would explain why my 96 car was such a pig when the EPS packed up.




Cheers,



James.

[mustdav]

NSA do you still have the spare EPS unit for sale???