Problem with torque sensor?
 

Hello all!

2015 BRZ with 25,000 miles on it. I had my rear driver side tire blow out recently and had to get a new quickly, so it unfortunately it does not match the passenger rear tire from a thread pattern and brand perspective. However, size and approximate wear do match (not many miles on the car).

I took my car in to get an alignment. The alignment was done properly, but the mechanic said he believes there is a problem with my torque sensor. When you step on the gas (for example at highway speeds) there is a significant pull to the left, and when you let off the gas the car goes back to the right. This phenomena does not happen at lower speeds on city streets. The mechanic said this excessive steering torque should be automatically corrected by the electric steering but it is not.

There are no error lights on the dashboard.

I am thinking of switching the front and rear driver side tires to see if the problem goes away (so that the two rear tires will be matched).

I told my mechanic this and he said he already tried this and it did not work. He thinks it is definitely a torque sensor/software issue and that I need to take it to Subaru before my warranty is up (that is a whole other issue. I have not hit 36k miles but have passed 3 years. I called one dealer who said ECU is not covered by the 5 year powertrain warranty but based on some Googling I think he was BSing me).

Any thoughts on this issue? Am I going about this the right way?

Thanks everyone for your thoughts. I wasn't sure what "technical issue" subforum this belongs in so I am posting in the general section for now.

You need two tires the same on the rear end or it will send the LSD into fits under certain condition. It is simple as that.
The electric steering does not compensate for anything. It is a simple assist.
Get a new mechanic since if he is blaming the ECU I am not convinced he knows how a LSD even works.

Yeah. This is a mechanical issue caused by having non-matching rear tires. You REALLY need to have the rears matching. At the very least, swap the fronts to the rears.

Also, find a new mechanic before he does something dumb to your car.

He was extremely extremely adamant that it was not a tire issue, though I like you both suspect it is, especially since there are no dashboard lights coming up.

He has 34 years as a mechanic and called a friend who works at a Subaru shop to assess the torque sensor issue he thinks there is. He also says he tried switching the front and rear tire on the driver side to match and still got the same effect. However, I am not sure he did this as when I picked up the car the tires were switched back. Not sure why he would switch them back if he did swap...

Are there any potential ECU updates I could be missing if I bought the car in Oct 2014? I do still plan to switch the tires tomorrow and test if the issue resolves itself that way.

Hello Tcoat,

In regards to the electric steering not compensating for anything, are you differentiating that from the torque sensor? Asking based on the info on this page:

"The control is provided by a torque sensor that is connected to the steering shaft; a computer tells the mechanism when it is needed to provide additional steering assistance."
https://www.citysubaru.com.au/blog/s...ower-steering/

Nothing having to do with what you describe. Even if it was a "sensor" issue, the yaw would be the result of the car intervening to correct what it THOUGHT was a slide. In that event, you'd be seeing lights on the dash, and feeling the power cut / ABS stepping in. The only thing that causes the car to veer in the manner you describe with no lights appearing on the dash is a MECHANICAL issue, such as mis-matched tires. At worst, it's a damaged differential.

If it was a damaged differential I would be having a whole bunch of other problems though wouldn't I?

I just read up on that steering sensor. I suppose the sensor could be broken, but I'm still not sure what your mechanic means by torque under acceleration or braking. It's like he's talking about the sensor correcting for torque steer, but these cars don't have torque steer... at least not unless something else is wrong. The sensor really shouldn't have to "compensate" for anything, but who knows, maybe it's fubared???

I would just rotate your tires before trying to dig deeper, though. It's an easy test to do before you start tearing your hair out.

Eventually, yes, which is why I think that's unlikely. I only really mentioned the diff because it's the only other thing besides tires or stability control that could drag the car to one side under acceleration, and the other side off throttle.

Yes that is how it works but it is not designed to compensate for abnormal changes in the torque. It is intended to work within specific parameters not adjust for changes due to the LSD.
This is really hard to find the right words to explain what I mean!

The Torsen LSD is a mechanical system that doesn't involve electronics at all.
There are sensors in the twins that mess with the brakes, but not the LSD.

It can be worn or trashed by running different drive wheel diameters - for a long time.
It won't get borked by a few miles, but a few months would cause problems.

[ame="https://www.youtube.com/watch?v=JEiSTzK-A2A"]Torsen Differential, How it works ? - YouTube[/ame]

Yes. Running two different tires on the back could very well have the diff act up without ever affecting the electronic traction control.

I Wikipediad torque steer and this paragraph seems to exactly describe what is happening; I bolded the most relevant parts:

"Torque steer is the unintended influence of engine torque on the steering, especially in front-wheel drive vehicles. For example, during heavy acceleration the steering may pull to one side, which may be disturbing to the driver. The effect is manifested either as a tugging sensation in the steering wheel, or a veering of the vehicle from the intended path. Torque steer is directly related to differences in the forces in the contact patches of the left and right drive wheels. The effect becomes more evident when high torques are applied to the drive wheels either because of a high overall reduction ratio between the engine and wheels,[1] high engine torque, or some combination of the two."

I know it says "especially front-wheel drive" cars but maybe my issue is part of the exception :(

Trying to clarify: are you saying there is no sensor that would adjust for torque steer in the car via the electronic steering? Or, would torque steer fall within the specific parameters of what the electronic steering should correct for?

Thanks!

You have two different tires on a LSD. There is no mystery here. The power steering is not meant to fix this and is not the issue.