Sunday, August 3, 2008


So after doing some research on why the EPS light would come on it's exactly like a check engine light. There are a set of codes that can be displayed to help diagnose problems with the system. The bad part is you can't use your standard cheap OBDII tool to read and clear these codes. The only scanners that will work for sure are from Honda and you can't buy them. There are some 3rd party scanners that cover most of the functionality and on average you can own one for 5k. Now I figured I was really in trouble here. After going over the electrical diagrams and service manual in general for many hours I found the loop hole I needed. It turns out Honda installed a backup way to do all of this in case your scanner software wasn't up-to-date! It turns out the EPS was complaining there was no vehicle speed signal and no engine rpms. I reset the codes and then made sure both spoofed signals were in place and the problem went away. It also turned out I was only getting a partial assist boost. Once I removed the dtc codes the boost is now very noticable.

How to retrieve subsystem DTC codes:
1) Bring the SCS to ground. This is pin 1 (at least on this vehicle). Unless you have a scanner which can do this, simply take a wire and stick it into the pin 1 hole. Then attach the other end to a ground on the vehicle. I believe pins 12 and 13 are also ground and you might be able to use of them but I didn't test this.

2) Turn the ignition ON. All subsystems will now begin displaying their DTC codes through their indicator light in the dash. Note that if a system doesn't have any codes the light will remain on or off. The light will flash for each number so count the flashes. It will also alternate between slow and fast flashes per digit. For example a code of 23 would be two slow flashes followed by three quick flashes.

3) Look this code up in your service manual to determine the problem. Each subsystem also has a crazy way to reset it. The EPS involved turning the steering wheel full left to center a couple times with pauses in between.


Peter said...

you are my hero~ I have been considering what chassis to use for an EV conversion and the s2000 is my all time favorite car, I think I will plan on copying your efforts next year when I have enough saved for the project~

Kennie said...

from one S2K owner to another: you rock dude...

Gabriel said...

it's a very good conversion

how did you achieved to turn on EPS system with the engine stoped

can you answer me to my e-mail, or to

Brian said...

The EPS currently turns on as soon as the electric motor begins to spin. I think in my next generation computer I build I'll pulse a false signal to the EPS to activate it when you turn the key on so you have initial assist before you start moving.

Saeid said...


Today, suddenly, my speed dial was showing 0 and no millage was being recorded, then the EPS light came on.

any ideas how I can get my speeddial to work again and the EPS light turned off?


Brian said...

I remember reading in the service manual about that. These numbers are kinda off the top of my head but the principal still applies. If the engine RPM shows over 2000 for more a minute or the MPH is greater than 5 for a minute or so also it will trigger an error with the EPS system.

First you need to figure out what's wrong with the speed signal and get that fixed first. This is what caused the EPS error code. After it's fixed you can then reset the EPS system as I mentioned in the blog or take it to a Honda dealer for them to reset. If you reset it before fixing the problem it will just trigger again.

Saeid said...

thanks Brian

it was kinda sudden as i was driving at a constant speed of approx 70MPH on the motorway. the PRM still shows up as usual but the speedometer, odometer and the trip meter have all stoped working!
ill take it to honda tomorrow and update you on it.


Saeid said...

by the way,
could this be a problem with VSS? (vehicle Speed Sensor?)

Brian said...

Most likely and hopefully as it would be the cheapest to fix.

I don't think it's the dash/gauges computer since the EPS is showing an issue too. The signal is split to both units and both are showing a problem. If not the VSS, sadly that only leaves an issue with wiring and will probably cost more as they try to track that down.

Good luck Saeid!

Onion said...


Your build is awesome, loved the read and photos!

Unfortunately, I have a problem with my EPS and I still can't figure out how to fix it, nor does the dealer.

So would you be able to help a brother out?

Please email me on how to reset the EPS unit myself w/o the PGM tester!


Brian said...

Not sure how else I can help. The steps above will retrieve and clear the DTC codes without the PGM tester.