Power Steering - EPS

[Kaz-kzukNA1]

Hi, all.

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

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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.

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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

[markc]

It never ceases to amaze me the lengths that some people will go to effect a bodge rather than properly repair a car :(

No doubt HUK would have told the previous owner that the "repair" was to replace the EPS controller and/or the steering rack at an exhorbitant cost but even so the bodge he chose to do is extraordinary.

Fabulous job Kaz, proper service and maintenance in action. Please don't leave this community anytime soon :)

Regards

Mark

[Senninha]

........Fabulous job Kaz, proper service and maintenance in action. Please don't leave this community anytime soon :)

Regards

Mark

I absolutely second this comment.

regards, Paul

[Midnight Blue]

[quote=kzukNA1;64046]Hi, all.

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

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.

Hi
Snowman reaired my EPS using the higher rated relays. They were not quite a direct replacement fit but they can be fitted.

Regards,

Andy

[bobbyswanbourne]

Just to confirm I am the lucky owner. Bought it from a TVR dealer who told me the PAS would cost £1500 to fix.... :):):)

[nigel]

Sure hope you bought Kaz a few pints and slipped him a fiver.
Kaz, once again your the man!!

Cheers
nigel

[mustdav]

Kaz my EPS has just failed with a code 22 and the new unit is £1500. I noticed that they had had the same problem on the Accura NSX in th US and that Honda increased the warranty on this part to 8 years but I'm now well out of that unfortunately.
So is this the relay problem and where do I get a relay cos I am wanting to sell the car??

[Papalazarou]

Kaz my EPS has just failed with a code 22 and the new unit is £1500. I noticed that they had had the same problem on the Accura NSX in th US and that Honda increased the warranty on this part to 8 years but I'm now well out of that unfortunately.
So is this the relay problem and where do I get a relay cos I am wanting to sell the car??

Two days after I bought my first NSX (a 96 car) the EPS failed. Honda quoted me £1300,00 for the control unit. We then negotiated it to £800.00 including vat.
Basically, I bought the control box from Honda and a few weeks later sent the faulty control box to BBA reman who fixed the relays. Obviously I should have done this before I forked out the £800 but I was new to the NSX and didn't know any different.

You are right about there being EPS issues in the States, but apparently they were confined mostly to 95 cars and the recall was US only according to the info I found on Prime.

Anyway, I would suggest either sending the control box to Kaz or contacting BBA Reman.

It's got to be cheaper than the HUK route.

Cheers,


James.

[Kaz-kzukNA1]

Hi, all.
Recently, another owner contacted me with EPS failure code #22.

His EPS controller was the old version of parts no. 39980-SL0-023 which was equipped with standard spec relays that would fail after lots of EPS usage by overcooking the relays.

Honda modified the relay spec from 39980-SL0-305 onwards and it replaced one of the two relays to the high current capacity spec to overcome the common failure mode of error code #22.

As it was possible to get hold of the high current capacity relays from US this time, it was agreed to drill the extra holes to the existing board.


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The standard spec on the left and the high current capacity one on the right. As you can see, the switched terminals have 3 pins compared to just one on the standard spec.


Although Honda replaced just one of the relay with the new spec, it was decided to replace both of them to the high current capacity ones for this owner. This means that I had to drill extra 8 holes on the existing board.


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After the preparation, new holes were drilled. Quite delicate touch was required....


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After creating the new holes, the coating was removed to enable the soldering joints around the 3 pins terminals. As new holes won't be a through hole joint, it is important to create strong connection each other.


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Installed the new relays and quick test was carried out to confirm no short circuit after the modifications.

The owner installed the modified EPS controller and happy with the result.

Hope he will enjoy the EPS.

Regards,
Kaz

[Sudesh]

Great work as always Kaz!

I guess cars with EPS also loose a tiny bit of leg room on the passenger side? Never measured it up to see, have you any specs Kaz?

[unloaded]

Thanks Kaz the new relays are definitely up to the job - lots of testing completed....

Sudesh - not sure if EPS looses leg-room or speaker room. The EPS unit sits behind the passenger footwell speaker enclosure, I wonder if the enclosure was adjusted to fit EPS rather than loose leg-room?

[Sudesh]

Yeah I know, thats why I asked about leg room as the speaker is still the same, but mounting bracket changed. Had a good look today and think leg room isnt affected as the cars without EPS use quit a long bracket, where cars with EPS have a different setup with part of the speaker bracket mounted to the EPS.




Thanks Kaz the new relays are definitely up to the job - lots of testing completed....

Sudesh - not sure if EPS looses leg-room or speaker room. The EPS unit sits behind the passenger footwell speaker enclosure, I wonder if the enclosure was adjusted to fit EPS rather than loose leg-room?

[Midnight Blue]

You can get the uprated relays from RS online. Only mail order. I think they were about 3 pounds each + postage (which was as much if not more than the relays).

regards,

Andy

[AnthP]

Hi Kaz,

I am a new member to the site althoyugh I've had my red 97 UK targa /auto (R134 TLF, then 9LEN, now SOF7E) since last December.

I read with interest this thread after a recent "£1600 discussion" with Honda about a new control unit (after waiting 3 months for them to get their hands on the correct testing gear and paying £200 for the diagnosis).

I've tried the clock fuse "trick" which solves the problem for a day / hour / minute but clearly this isnt a long term fix for my car.

I also replaced the battery which seemed initially to provide a temporary fix but clearly, there is a problem with the unit.

I was wondering therefore whether you could work your magic on my unit ? - if you can, could you please let me have an address and I'll get the unit sent to you.

I look forward to hearing from you.

Best Regards




Anthony

[Kaz-kzukNA1]

Hi, AnthP. Thank you for showing your interest to my services.

Could you kindly send me an email by selecting the option when you click on my user name?
‘Send email’ option is only available after you have logged in.

For me, it’s much easier to organise all of the communications through email than PM or through a certain thread as I receive so many questions every day and I’m not always on the NSXCB site.

EPS can fail in several ways and it is important to know the exact failure code before I can offer my service.

Several owners have already contacted me on the EPS and A/C CCU failures ahead of you so I need to put priority to them.
At the same time, I need to look after several owners who have already paid for their parts in order to have several services on their NSXs. So, it may take some time but at least, we can talk about the failure code/mode through email.

Looking forward to hearing from you again.


Regards,
Kaz

[Kaz-kzukNA1]

Another owner contacted me with EPS failure. The owner managed to confirm the EPS error code that was #22 and he also managed to take out the EPS controller out of his NSX so the unit was sent to my place for service work to be carried out.

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The controller was once again ver.023 that tends to fail after a while.

The unit was opened and both relays were removed. When tested on the bench, one of the relay was showing fluctuating resistance between the switched terminals even when 12V was applied to the coil side. This will definitely cause EPS error code #22.

As the demand is not that high compared to the A/C CCU service, I normally don’t stock the parts for EPS.
The specific high current relay is not available in UK and only stocked in Japan or US so while waiting for the delivery of the parts, decided to drill the holes on the board.

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By the way, when I opened the lid, I was expecting to see thin clear protection sheet behind the lid. This is to prevent the short circuit from happening in case someone dents the lid and hit the board with metal lid. Probably the unit was opened in the past or simply it was not there from the beginning.

New holes drilled for the upgraded relays.

So, just need to wait for the delivery of the parts.

[Kaz-kzukNA1]

Decided to inspect the faulty power relay.

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After opening the outer housing, it was quite obvious that the spec of relay was not suitable for the task.
The contact was burnt and even melted causing intermittent connection and not being able to pass through enough current through the EPS circuit and casing error code #22.

Later Honda upgraded the relay spec to the high current capacity one but if you have EPS with last three digit of controller part no. -023, then sooner or later, it will fail.

Hope I can help this owner by replacing the relays.

Kaz

[Kaz-kzukNA1]

Finally, the parts arrived from US and installed into the EPS controller.

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As in the old post, the standard one on the left and the high current spec used on the latest controller on the right.

Although the continuity check was fine, the fitting of one of the relay was quite tight especially at one of the control line. In case the through hole was damaged when I inserted the relay, one jumper wire was used to strengthen the connection.

Both relays were replaced, conformal coating applied to protect the new soldering joints, tested and confirmed no short circuit after the service and ready to be returned to the owner.

EPS can fail in many ways and if there is another issue such as torque sensor failure addition to the error code #22, replacing the relays won’t solve all of the EPS issues but at least, it is better than paying more than GBP1,500 for the new EPS controller.

Kaz

[AnthP]

Kaz,

You are a superstar !

My wife rang me today to say the unit had arrived so I raced home to reinstall the unit - one hour later, EPS restored !

Great service, daily updates, great price, great result !

Almost looking forward to my next problem !

Thanks a million

Cheers



Anthony

[John C]

My power steering has recently failed, but I find driving it still OK. The car is really outside my budget, but I just love it too much. Am I likely to do any damage if I continue to use it without getting it checked?

[Sudesh]

My power steering has recently failed, but I find driving it still OK. The car is really outside my budget, but I just love it too much. Am I likely to do any damage if I continue to use it without getting it checked?

If possible try and get the fault code, but to answer your question "if it's still ok to drive" then, from what I gathered YES. There is no "pressure" to speak of, as the EPS is an electric motor, not a hydraulic system. Kaz will point you in the right direction though, as I have not worked on many EPS systems yet.

[Kaz-kzukNA1]

My power steering has recently failed, but I find driving it still OK. The car is really outside my budget, but I just love it too much. Am I likely to do any damage if I continue to use it without getting it checked?

Hi, John C.

EPS can fail in many ways.
On a certain case, it is fine to drive even with the EPS error because the controller is simply disabling the EPS but for other cases, you may cause extra damages inside the EPS rack if it is not addressed soon.

If it is error code #22 and if you didn’t have any other issues such as torque sensor failure or mechanical issues, then you may be able to fix the issue by replacing the power relays inside the EPS controller.

For this specific case, you are most likely to be fine driving with EPS error.

This is very likely to be the case if your EPS controller is #39980-SL0-023.
You can find the part no at the side of EPS controller case.


However, even if the error code was #22, you won’t be able to fix the issue by just replacing the power relays if you have mechanical failure.

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This photo is from KSP Engineering in Japan and it shows one of the example of EPS failure with error code #22.

Even they replaced the EPS controller with known good one, the issue was still there and when they opened the EPS rack, it was full of rust.

The tierod/rack end dust boots were not installed properly and moisture got inside the steering rack causing lots of trouble. They managed to repair it but not something you want to do everyday.

If your torque sensor has failed, you will get additional error code and I’m afraid, at this stage, it is not possible to repair it. My friends are working on the replacement interface circuit at the moment.

So, first, please try to read the error code and ideally, check the part no on the side of the EPS controller case.

Kaz

[XaviCR]

Hi, My EPS has code #26, you can help me? What could be the problem?

[XaviCR]

I download the 1998 manual,

Code #26: "The Upper FET is stuck ON" see page 17-36....


but I don't have the page 17-36 :(

[Kaz-kzukNA1]

Hi, XaviCR.

EPS error code #26 was introduced only after Feb/97 models in Japan so presuming your NSX is UK spec, it would be the later models.

From these models, the rotation sensor was removed from the EPS rack and EPS controller hardware/software was also modified and thus, you should already have the latest spec power relays inside the controller.

Any other failure codes other than #26?

Did you experience any battery failure or jump started the NSX before getting the error code #26?

Did you fail to start the engine just before getting this EPS failure? Have you replaced your Main Relay already?

Can you remember the condition/situation when you triggered this EPS failure?

How is the condition of your battery terminals?
How old is your battery and do you use battery conditioner if you don’t drive your NSX regularly?


EPS error code #26 is only detected just after starting the engine until the EPS warning light distinguish itself so it's quite short period.
Once it is triggered, unless you reset the error code, EPS will be disabled.

If you checked all the connection to the EPS controller, EPS rack, battery terminals and battery itself, then please park the car with the steering straight and stop the engine.
Then, reset the EPS controller by removing the 7.5A clock fuse. Please note that this will also erase all of the engine ECU related study value.

Start the engine without touching the steering wheel. Please note that as you erased engine related study value, you may find your rpm going up and down for a while.

If you no longer get EPS failure, then stop the engine, re-start the engine and this time, turn the steering wheel left & right all the way.


This would be enough to start with as you have lots of things to check.

I have the manual even for this error code #26 but it’s all in Japanese with several diagrams…
Not easy to translate all of them and explain the procedure….

Kaz

[pralognan]

My EPS stopped working today,warning light on continuously. Reading the error codes gives 34,36 and 38. The manual 19-46 gives34,38 as rear wheel pulsers which fits with my pre-existing ABS fault when pedal kicks back when coming to a halt and pump "chatters". Not sure what code 36 means,Any ideas would be welcome.

[Kaz-kzukNA1]

Hi, pralognan.

As for any technical questions, it will help if you can provide some basic info on your NSX.
Could you provide at least the Country spec, Year model, NA1/2, 5MT/6MT/4AT, any modifications, etc?

It will help if you can provide me with the first 7 digits (the characters shown as ' * ') of your VIN after the JHMNA*******.
Please do not post your full VIN on here for security reason.

Also, which error code (EPS, ABS, TCS, CEL, etc) did you read?
EPS does not utilise individual raw wheel speed signal for its control loop so I think you read something else.


Kaz

[pralognan]

Dear Kaz,
UK spec,1991 model year,NA1,,4AT. JHMNA12600T0.No modifications except for Dali rice rocket aftermarket exhaust. I was reading EPS error code.
Thanks for super quick reply.

[Kaz-kzukNA1]

Hi, pralognan.
Thank you for the extra info.

Based on your VIN, I can confirm that it is indeed 91 model with 1st gen EPS system that has both the torque and rotational sensors on the EPS rack and the EPS controller is separated in 2 boxes as the Power and the Control units.

The reason I asked you about the error code was your reference to the workshop manual 19-46 in your post.
Section 19 is for the 'Brake (ABS)' and your very page is for the ABS warning light and not for the EPS one unless I’m missing something not in your above post.
Anything to do with the steering including the EPS is always in Section [Edit: 17] for NSX [Edit: English workshop manual].


Also, there is neither #36 nor #38 for EPS error code unless you magically managed to put the EPS controller into a different mode so another reason for requesting the clarification of which error code (warning light) you read.


By the way, as in my previous post above to another owner, did you jump start the car or had difficulty in starting the engine recently?

Could you kindly read all of the error codes including any other warning lights again?

Then, I recommend you to double check the battery connection for any loose connections especially at the GND terminal.

Once these are done, then as in my above post #25, please remove the 7.5A CLOCK fuse for more than 10sec to reset the error code on the EPS controller.
This will also reset the ECU but I’ll leave it for the moment.
Start the engine and if you don’t see the EPS warning light, carry out the test driving session until you trigger the EPS warning light.

Once you saw the warning light, please read the error code again.

Kaz

[pralognan]

Dear Kaz,
Thank you for your reply. I thought sunday would be your day off! My copy of the manual deals with steering in section 17,and there I found code 34 for EPS control unit fault. The memory also showed faults 36 and 38. Not a magician,just retired Denso radiator man! Never jump start or difficulty starting.No other warning lights. All 3 codes,34,36,38 on the EPS red light.
This morning nice spring weather so investigation showed bad battery connection to GND. After battery removed and refitted(equivalent to clock fuse removal), no warning lights and test drive up a twisty mountain road all OK

[Kaz-kzukNA1]

Yes, you are correct. I should have written Section 17 and not 11 for the English manual.
Just found out, 11 was for the Japanese manual.
Still, it’s not Section 19 (probably typo???) and also there is no EPS error code #36 or #38.......

Glad that you managed to clear the code and carried out the test driving session with no further code.

It is possible that the codes were recorded long time ago and never cleared even after the issue was fixed (though, not sure about EPS #36 or #38).
You seemed to know the importance of reading the error code before clearing it (unlike the suggestions of ‘pull the clock fuse and drive’ on many other forums) so next time when it happens, you have already created the clean memory bank on EPS controller so that you can diagnose it further.



PS.
Day off on Sunday.... I wish.....
When I used to travel for the race weekend every week or two, just kept working through the weekend, fly back late Sunday night or following day and back to the office straight away before flying out to the next country in a few days and work through the weekend again. Repeat this until the end of the season but then the test events starts so endless.....
After over 20 years, got used to such life style though.
Now I don't need to travel any more so can focus on NSX more.

Kaz