Honda Civic EPS conversion
 

I am working on converting my 2005 Honda Civic to EPS from the hydraulic assist that it came with. Unlike most people on this forum, my primary reason for doing this is performance and cleaning up the engine compartment more than gas mileage. I have been building this car for better performance mostly. Specs for my build will be posted soon. However, fuel efficiency was a reason to convert to EPS too.

Also, another reason that I am converting to EPS is so I don’t have to worry about getting power steering to work or getting compatible hydraulic hoses when I swap to a K20 or K24 engine in the future. So in a way, I am futureproofing for a K swap in the future.

So the first step was to find a used EPS system to install. I found an EPS rack and an EPS module from a 2004 Civic hybrid for a total of $90, which seems like a good price to me. I don’t have the wiring harness yet though.

I ended up installing the EPS rack anyways though. The install was pretty straightforward and easy except for one a couple of things: First problem is that I had no room to work with the D16Y8 intake manifold that I installed, so I had to remove the intake manifold to get it in. Second, I didn’t get the brackets that go with the new EPS rack, so it didn’t fit correctly. The passenger side of the rack had a random chunk of metal under the mounting hole, which kept the rack from sitting flat on the bracket. But once I chopped off the random chunk of metal, the rack bolted in perfectly just like the OEM rack. I will upload pictures when I get home.

However, if you choose to do this swap, I would suggest getting both brackets just in case. You could probably get away with just replacing the passenger side bracket, but I am not certain since I never tried it. For all I know, the rack might not sit straight if you replace only one bracket, so I would suggest getting them both just to be safe.

But other than that, the installation of the rack was easy. I used the OEM tie rod ends and the tie rods that came with the rack, but I am pretty sure that they are the same.

I still need to get an alignment since I aligned it by eye, but so far so good. The car drives fine with this rack. The steering is easier than it would be with the OEM rack when the assist isn’t workiing, but it is still pretty hard to turn since the electric assist isn’t connected yet.

So the last step is to connect the wiring. From my understanding all I need to connect is constant power, power when the key is on, RPM signal, VSS signal, and ground. It probably would be a good idea to connect it to the OBD also so it can be scanned for codes if there is a problem. Also, I have no idea why the control module would want an RPM signal since there is no pump running off the engine, but whatever.


So that’s where I am at right now. The rack is in, so I just need to find a wiring harness and connect it.

Anyways, that is what I am working on right now. If anyone has any questions, comments, or suggestions, feel free to post

You're not the first guy I've heard of, installing an EPS system to free up a few ponies for better performance. Decluttering the engine bay has got to be a plus, too.

What I had been seeing though was that for people looking for an off-the-shelf option, they were splicing in the business end of a Prius column to get the motor and rack. The Prius has some speed-sensitive hardware that it needs for proper function, but in a non-Prius install it defaults to a certain level of assistance so even when lobotomized it still works.

My experience in my HCH was there was a small range of deadness at the center of the steering where it gave no assistance, and beyond that it would suddenly jump in with added torque, causing a jolty ride if you weren't ready for it. I never dug into it much to try to adjust that out, I just got used to it.

Thank you. Just out of curiosity, does the EPS system work without the engine running? I know that it could, but I am not sure if it would since it needs an RPM signal.

I have heard the same thing that there is a little deadness at the center of the steering wheel, and as far as I know there is no way to adjust that. However, I have also heard that Honda updated the control module for the 2004 and 2005 models to help address that issue, although I am not sure if that is true. I do know that the part number for the control module is different though.

That is very interesting what you said about some people using a Prius steering column, that sounds like it could be a good option for someone looking to convert a car to EPS where there is no OEM option available. Another option would be an electric pump that only runs when needed, or installing a clutch on the belt driven pump so it only runs when needed. I thought about trying to find an electric pump, but I decided that it would be easier to install an OEM EPS system than to try to build something custom.

Thank you. Just out of curiosity, does the EPS system work without the engine running? I know that it could, but I am not sure if it would since it needs an RPM signal.

I have heard the same thing that there is a little deadness at the center of the steering wheel, and as far as I know there is no way to adjust that. However, I have also heard that Honda updated the control module for the 2004 and 2005 models to help address that issue, although I am not sure if that is true. I do know that the part number for the control module is different though.

That is very interesting what you said about some people using a Prius steering column, that sounds like it could be a good option for someone looking to convert a car to EPS where there is no OEM option available. Another option would be an electric pump that only runs when needed, or installing a clutch on the belt driven pump so it only runs when needed. I thought about trying to find an electric pump, but I decided that it would be easier to install an OEM EPS system than to try to build something custom.

Neat project! Following with interest.

The Civic Hybrid EPS is one of my least favorite EPS systems, but I imagine it to be the easiest swap. Insight and Fit EPS have much smaller dead zones and lighter steering, though I suppose that could have as much to do with the weight of the vehicles in question as anything.

I'm about to do a K swap in my Insight and I'll report back on how my EPS functions. From what I've gathered from others, K series tach signaling is different but EPS still works after the swap it's probably only used for some of the logic. EPS in my car works whenever the key is in the 2 position even if the engine is off.

Great info, thank you. I think that the RPM signal might only be used for error checking somehow. I say that because there are EPS trouble codes that are set based on the RPM/speed comparison. For example, "The car’s RPM is less than 500, but the car's speed is 6 MPH". Why it would care I have no idea, maybe to help verify that the VSS signal is correct.

As for the K swap you are planning on doing, that's awesome! I don't expect that you will have a problem with the EPS. The Civic EP3 comes with EPS, and people have also done EPS conversions on their RSX with no problems.

Also, I would imagine that the EPS module makes a big difference in how the steering feels and responds. I have the Civic Hybrid EPS module, but I have heard that the Civic SI EP3 module might be a better choice because it is programmed for a heavier, more sporty steering feel, where the Hybrid EPS module is programmed for a lighter, more relaxed steering feel. I have no idea if that is true, but it's what people have said.

As for the dead on center feel, I was kind of concerned that my rack would feel loose and unresponsive because it has a torque sensor on the steering input, so the shaft can be twisted a little bit in both directions without moving the tie rods. However, I can feel no additional play or deadened response at all, which I am very happy about. Actually, this rack feels better with no assist than the hydraulic rack felt when it has no oil in it or when the belt isn't on the pump.

I don't know if the Prius EPS needs an RPM input - Prii can do engine-off EV operation up to 40+mph in my Gen2. What I read was that the Prius EPS, installed in a car that was too analog to provide such info, nevertheless provided some assistance. It didn't turn up to higher assistance at low speeds like you'd expect, but some assistance is better than nothing.
I'll see if I can't dig up where I saw that and drop a link. I'm pretty sure I'm remembering it correctly.

I am almost done with the conversion. I will upload pictures as soon as I have time. I got a wiring harness from a buddy and I installed the harness. I needed to cut the harness and extend 8 wires total. I needed to extend the 6 wires for the torque sensor, as well as the 2 large cables that go to the motor. I made the wires a bit long, better to have a bit of extra length than have it too short.

Then I hooked up the VSS, RPM, and key on power to the module. I cut the harness to add the RPM and VSS wires on the car's harness rather than the engine's harness so I don't have to redo any wiring if I need to replace my engine harness again or when I K swap.

Then what I did is since I wanted to test it but I didn't have a long cable to connect the main power to the fusebox is I put an extra battery on the floor and connected the power and ground to the harness with jumper cables to test it. It worked! I didn't drive it with the assist working since I didn't have a way to power it, but it worked and it felt good.

So tomorrow I am going to get enough 8 gauge power cable to connect power to the EPS module and see how it drives. I will report back as soon as I am able to drive it with the EPS working

It's a Honda civic. Do you even need power steering?
I drive my 3/4 ton suburban with no power steering.

Define "need". I can drive it with no power steering, but it is actually pretty hard to steer when it's stopped. Like it pretty much can't be steered with one arm.

Also, if the car can't be quickly steered at a very low speed or while stopped, that is a safety hazard.

Besides, installing an EPS system is a lot cooler, more interesting, and more unique than just taking the system out :)

Gen1 HCH EPS rack... be prepared for extreme disappointment.

Hated every second of highway speed driving in that car.

Well hopefully it's not disappointing. But if it is, I could easily install a switch to manually shut off the assist on the highway. For that matter I could figure out a way to set it up so it disables itself above a certain speed too.

Here is one picture. I had to chop off the random chunk of metal circled in red to bolt it in with my OEM brackets

The installation is electrically complete. I installed a power cable from the fusebox to the module and went for a drive. The steering actually feels great to me! At low speeds the steering is extremely easy, but since the steering is speed sensitive, it feels firmer than the hydraulic system felt when the car is up to speed. It feels very predictable and responsive with no lag or deadness at all. To be honest if this wasn't my car and I didn't know that it has EPS I would not know that the system was electric from driving it. I guess Honda figured worked out the bugs in the system by 2005. That or I just got a good system

Here's a picture of the module installed in the car. Now I just need to mount it, clean up the wiring, put the carpet back, and put the interior back together

Might want to think about some sort of clamp mechanism to hold it on that side. Not knowing how much you cut off, it looks weak

Great point! However, I did not actually cut out anything structural, I just cut off the random chunk of metal under the bolt hole so it looks round like the OEM rack. Also, the OEM mounting bracket has a thick strip of metal that goes over the mounting hole for added strength. The easiest solution would have been to get OEM mounting brackets for the hybrid, but I didn't think to and by the time I realized that the brackets were different the rack was already out and I couldn't go get brackets.

Really glad it worked out for you! There are a lot of Honda folks on here, and I'm certain someone else will eventually follow your lead with this swap.

For what it's worth, the EPS rack is also great for manual conversions, there's a lot less resistance than with a hydraulic rack, but there are some things you need to do to it to make it work. Simply unplugging or even unbolting the EPS motor is going to leave a stiffer than necessary manual rack because the motor connects to the rack via a worm gear. The gear turns very easily from the motor side but not the other way around. Turning the rack without the motor spinning results in a lot of resistance unless you remove the worm gear as well.

See here: https://en.m.wikipedia.org/wiki/Worm_drive


Put another way, Honda's EPS racks have a large reduction ratio and unless the worm gear is removed along with the motor, a manual conversion with these racks leaves a lot of friction and drag, similar to how looping the lines in a hydraulic rack still results in high steering effort.

Q. Why would you ever want to do a manual conversion on an electric rack which is virtually free in terms of economy?

A. Due to the above property of worm gears, relatively little steering feedback is able to get back to the steering wheel.

That is really great information! I actually noticed that when the front tires are off the ground it is still quite hard to steer, similar to the feeling of if I was turning a hydraulic rack without the engine running. I wondered if it was drag from turning the motor, but then I remembered that the motor turned very easily when I had to take it out to get the rack in. I would say that with the front tires off the ground, the steering effort is the same as or slightly higher than with the tires on the ground and the EPS active, but definitely more drag than the OEM hydraulic rack with no oil in it.

As for converting the EPS rack to a manual rack, there is one little thing that you are forgetting: The torque sensor play. The torque sensor would introduce a little bit of play in the steering also because you are basically turning through a spring. I can't feel the play while driving, but if EPS isn't active and the car is sitting still, the play can be felt a little while turning. It isn't bad at all, it just basically feels like you are turning through a spring, but not that bad. But with EPS active, the play can not be felt at all.

But if you are going to go through the trouble of converting an EPS rack to manual for the purpose of achieving more steering feel and more precise steering, you may as well find some way to get rid of the play in the torque sensor or make a solid shaft with no torque sensor for the best possible results though.

Oh and I answered my own question on when EPS is active. If you turn the key on without starting the engine, the EPS system does not activate, the engine has to actually be started to activate EPS. However, once you start the engine, the EPS will still work if you kill the engine as long as the key stays on the whole time. Interesting. However, for the people who like to EOC, I guess it’s a good thing that EPS still works without the engine running.

That's how mine works too. Interesting.

I wonder why it isn’t active whenever the key is on. It’s possible that Honda did it that way to make the EPS feel like hydraulic as much as possible, so it only works with the engine running. Maybe because they don’t want the battery to drain. But on the other hand it only draws power when the wheel is being turned, and I can’t imagine that someone would sit there with the engine off and the steering wheel cranked all the way to one side long enough to drain the battery LOL

It likely wouldn't be hard to make it active all the time.

Good point. It doesn’t bother me that it only works with the engine on, I’m just curious why it works that way. Also, I’m not sure how I would change the way the system is designed. I guess one option may be to install some type of circuit or device that simulates an RPM signal whenever the key is on, if such a thing even exists. However, one potential problem with that may be that depending on what the module uses the RPM signal for, a fake/incorrect signal might mess with the way the module functions and cause problems. This may or may not have an adverse effect depending on what the EPS module uses the RPM signal for.

However, an easy and safe option if someone wants to retain steering assist once the key is shut off would be to connect the switched power for the EPS module to something powered by the ignition switch’s “ACC” wire like the cigarette lighter power rather than the “RUN” wire. That way the EPS system would remain active once the key is turned to the “ACC” position until the key is shut off completely.

I have another thought. Now that there is no power steering pump to run anymore, I am thinking about getting an crank pulley from a Civic without hydraulic power steering to reduce rotational mass a little by eliminating the power steering pump pulley. But there are other things that I need to buy for this car first, so it might be a little while