Hi,

I'm trying to reverse engineer my 2017 Acura ILX and I'm stuck with the steering torque sensor. I'm trying to trick EPS so it thinks that there is a torque applied to the steering wheel by the driver. By doing it, I hope I'll be able to develop a steer-by-wire system. I tapped onto the three signals coming to the EPS module from the steering torque sensor. Below is a wiring diagram and a high-level description from Acura.



It looks relatively simple and sounds similar to other cars. However, the voltage that comes into the EPS module doesn't change at all. It always shows 330mV between VS1 and PVF. The same for VS2-PVF voltage. I expected it to change when I steer, but no matter how hard I steer the voltage level stays the same.

Can anyone give me a clue on how it works?

Cheers

 

You cant figure out this simple device works yet are trying to reverse engineer it??

Geez.


Figure out how your meausering device works,understand what the description is telling you in regards to the variances in voltage. Once you understand that,you'll understand why your reading isnt changing



(I could give you the answer,but then you wouldnt learn. Heres a clue however: A meter is the wrong tool for the job)

 

When did I say I use a meter? I use an oscilloscope. I found an info that the signals are pulsing with 14.2kHz, but for some reason, I don't see it. You can again say "Geez", but I had no problems with, for instance, distinguishing CAN bus signals and I don't understand why I'm not able to see the pulsing.

Thanks for the reply though

 

I assumed meter because of the signal(or lack of) you say you got. If youre using a scope why would you care about frquency? You have no reference there

.Perhaps a better understanding of your tool will help me. What is the brand of your scope? Where are your leads at?(connected to?) What are your settings? How are you measuring?


***The last question is one of the most important

 

I'm using the Rigol ds1054z which I believe is suitable for this kind of job. Here is a little bit more description how I measure the signals:
I t-tapped onto the wires near the connector going to the EPS control module (all the connectors are in place and the steering is operational, there are no faults on the dash). I measure the difference between VS1 (supposedly, the first signal) and VPF ('Continuity to ground'). Below is the picture I took.

I'm confused about this sine wave. The VS2-VPF is almost identical. In addition, when I turn the steering wheel, nothing seem to happen: I see the same sine wave with the same amplitude, with the same mean value (it doesn't go up or down)
At some point, I was experimenting and had only one terminal connected to VS1 without connecting the second (negative) terminal to VPF and somehow I was able to get this picture (sorry about the quality)

This looks somewhat similar to what I think it should be, but when I tried to replicate it to take a better picture, I wasn't able to.

Let me know if you can provide some hints.

Thanks in advance.

 

I am unfamilar with that scope,it is not an automotive scope,it matters because the filtering,aliasing and such vary between scopes. I use a PicoScope.

With that said,it looks like the settings on the scope are wrong. Again I am not familiar with it,but it appears in the second screen you are on a 50v per division setting and 5 sec time base. You should be at 1v per and no more than about 500ms


Additionally,the wheels need to be on the ground when turning side to side and checking for the signal.

 

Thanks for your replies. I'm still struggling with it. Can you please share additional details on:
1) as far as I understood, PVF is a pulsing signal, not a still ground. Do I need to measure VS1 and VS2 with respect to PVF or a plane ground?
2) do VS1 and VS2 signals also pulse? As far as I understood they do pulse with the same frequency as PVF, but their amplitudes change. Do they, or they act more like PWM signals when their amplitude stays fixed?
3) I found a similar project but for Honda S2000 (Modifry Products - Freebies). The schematic looks almost identical to what I have on my Acura. However, I was unable to reconstruct it. As soon as I insert even small identical resistors (22Ohm) to the both VS1 and VS2 channels - I get a fault. Let me know if you can comment on that.

Any information would help. Thanks again.

 

PVF is an NPN transistor to ground. Meaning it is not a constant ground. Use a regular chassis ground and channel 1 on VS1 and channel 2 on VS2
Yes,with respect to input from the torque sensor. Thats why you need a scope.
There is not ienough information for me to infer one way or another. You have to scope the signals.Im not sure,it could be (and is likely) that your PCM is more advanced than his and it is looking for a certain resistance value. If it doesnt see the value it expects it sets a code.

You can try contacting that individual and question him.

 

I feel like I'm being misled by an Acura service manual that wasn't properly updated for my model or something like that. I get it at the techinfo.honda.com and supposedly it should be legit.

Surprisingly, PVF looks like a constant ground. I can see only a very small noise when I compare it to a chassis ground or one of the grounds used in the EPS module. They are level. Like you said, the NPN transistor on the schematics suggests pulsing...

I did - he can't help at the moment and as you pointed, his EPS appears to be simpler.

Today I was messing with the car again. The engine was off, but the ignition was on, so the EPS module and the torque sensor was on, but the EPS motor was off, so the steering required a lot of torque from the driver to turn the wheels. And I might have finally noticed something.
Here are two channels when I don't touch the steering wheel: there is a slight bias but they are almost equal. The sine waves frequency is around 25kHz and I measured them wrt to PVF. If I measure them wrt to the chassis ground - I get the same result.


Here are the signals when I try to steer left:


Here I steer right:


When I turn the steering wheel, it appears that one of the signals shrinks and the other one amplifies a bit (depending on the steering direction). It makes sense - I expect something like that.
But the change is so minuscule! As I said earlier, the EPS motor was off, so I had to pull the steering wheel really really hard. No wonder I wasn't able to notice any changes in voltage when the EPS motor was on and helped to steer.

Can it be the case that the EPS evaluates such small voltage changes? I can imagine that any interference by an electric device near the wiring, or a torque sensor coil deterioration can introduce a bias... Why would Honda take this design route? Am I missing something or the EPS module is really looking at such small voltage changes?
In addition, the service manual says that the signals pulse between 0-5V which is not the case: the total sine amplitude is about 1V and it's strangely shifted wrt to the ground by ~300mV.

Let me know if you have any thoughts.
Thanks

 

Hi Vadbut,
I try the same thing with my CRV but no luck, have you found the reason?

Duc