Alf_09NFR

Is it possible to replace the EPS torque sensor with the steering rack in the car? Don't know if I will need to, but I just want to scope the work so I'm not surprised.

The symptoms below have been reported by others (See this topic), but this car (a 2009 AP2, 30k miles) is NOT showing an EPS error light.

Steering is very light/easy when turning the wheel to the right (anywhere from lock to lock), and hard/normal when turning the wheel to the left - again, all the way from lock to lock. Not a wheel alignment issue, car showed the problem both before and after alignment.

I tried the neutral position learning process (and the code clear process which is the same, except you turn the key off before the final 3 blinks). I only got the blink code (14), and never got the appropriate behavior from the light. The manual says turn the wheel 45 deg left and hold it, Billman says 45 deg and let go - neither worked. It just showed the blink code. Couldn't clear it, but no EPS light.

Code 14 says EPS torque sensor wiring problem. I'll check the wiring this weekend (didn't have my multimeter when I looked at the car last night).

I do want to know: Can the EPS torque sensor be changed without removing the steering rack from the car? (The book only shows replacing it with the rack removed).

Thanks all...

Billman250

Relearning the neutral position is tricky.

I take back what I said about letting the wheel go at 45 degrees.

Slowly turn the wheel 45 degrees, and hold it still with maximum resistance. It should be fighting you with the grip of the tires.

when returning to straight, get it to straight fast and let it go.

Alf_09NFR

OK, I'll try again... but - in case I have to replace it - do you know if the TS can be changed with the rack in the car?

Billman250

I would imagine so but I am not sure.

Alf_09NFR

Thanks.

Anybody else know if you can swap the TS with the rack in the car?

Billman250

The TS assy has a pinion gear that extends out about 2.5 inches beyond the mounting surface. The entire unit is pretty small.

I'm guessing replacing in the car would be simple.

Alf_09NFR

Thanks! It looks like you just need to get the steering shaft disconnected and out of the way... how hard could that be?

If I have to replace it, I'll let you guys know how long it took, etc.

I'll also have a look inside and see how it works, what broke , and whether it can be fixed.

Jim

Alf_09NFR

Well I finally got around to fixing the EPS problem.

To restate the issue, this car (2009) had uneven power assist. No EPS codes, it just had a lot more assist when turning the wheel to the right (anywhere from lock to lock, there was too much assist turning right, and no assist at all turning the wheel to the left). Tried to reset the center position, but it was very, very hard to make it through the sequence, and when I did successfully complete it and get the 3 confirming flashes (after about a dozen tries), no change - the steering still behaved the same. I did some troubleshooting with a scope, and decided the torque sensor was the culprit. The car was drivable, but it sat in the hangar for the last couple of months - weather was cold and miserable, snow, rain, ..., not ideal for driving the S.

I ordered the new TS (~ $300), and finally got around to installing it today! The weather is getting nice, 60F and sunny today, and the owner decided winter is over and she wants to start driving it again.

So here is the step by step for replacing the TS without removing the steering rack or messing up the alignment (which I had just done).

1. Remove the air intake, unplug the connector on the TS.
   
2. Put the car up on jack stands, center the steering wheel.
   
3. From underneath, remove the two bolts from the steering coupling and slide it up the steering shaft. Don't worry about marking it as you're going to replace the TS anyway.
   
4. Loosen the steering rack preload bolt one full turn. Don't skip this step, you won't be able to install the new TS unless you do this. You have to loosen the big lock nut first, and you probably don't have a wrench that will fit. I took 10 minutes to make a crow's foot wrench (see attached photo) from a 3in by 3in by 1/4in scrap of steel. You might be able to use a spud wrench, crescent wrench, big slip joint pliers, or...?
   
5. Remove the 2 bolts that hold the TS assembly into the steering rack, and pull the TS from the steering rack.
   
6. Grease the gear and pilot shaft of the new TS, and rotate the shaft so that the stamped letters on the shaft are on top when the TS is positioned as it will be when installed. This is how you want it to look after it is in the car. Notice the teeth on the gear are not straight, and when you push the TS into the rack it will cause the TS shaft to rotate, and the stamped letters on the shaft will no longer be on top. Darn. So rotate the shaft about 20° or 30° so that when you push the TS into the rack the stamped letters on the shaft will end up on top.
   
7. Make sure the o-ring is in place on the rack, and that you've put the dust shield on the TS shaft (my new TS came with new o-ring and dust shield, but if you're using an old part...)
   
8. Double check that the wheels are still pointing straight forward. Push the TS assembly into the rack, very little force needed if you loosened the preload nut in step 4. Make sure the stamped letter ends up on the top of the shaft! If not, pull it back out and turn the shaft a little more or less and try again. When you get it right, reinstall the bolts and torque to spec.
   
9. Adjust the steering rack preload bolt that you loosened in step 4. Tighten the adjustment bolt to 18 lbft to seat the parts, then loosen, then torque to 3 lbft. Tighten the big lock nut while holding the preload adjustment bolt.
   
10. Double check that the steering wheel is centered, and the wheels are straight ahead. Back under the car, slide the steering shaft coupler down into position, reinstall the bolts, torque to spec. (A little Loctite on the threads will give some peace of mind as you're carving through that 80mph right hand corner, and your thoughts flash back to this bit of repair work...)
    
11. Plug the connector in on the TS, reinstall the air intake and anything else you took apart.
    
12. Put the car back down on the floor. Collect all your tools, make sure the intake air temp sensor is plugged in – duh.
    
13. Do the TS neutral position learning exercise (detailed by Billman and others in another thread). With the new TS, it worked the first time!

Start to finish took about 90 minutes, but that included making the wrench used in step 4.

Billman250

Thanks for returning to the thread and posting your solution

Alf_09NFR

I opened up the TS, and if the problem is electrical there is probably no way to fix it. The sensing coils are cast into the plastic housing.

Mechanically, the shaft that goes through the TS has a spring loaded coupler of some sort between the steering wheel end and the pinion gear that goes into the steering rack (did not tear it apart more than you see in the picture). When you turn the steering wheel, the input and output shafts rotate a bit with respect to each other. There is a pin through the shaft that engages the diagonal slot you can see in the beige plastic part, causing it to move up and down the shaft a distance that is proportional to the amount of torque you are applying to the steering wheel.

The EPS computer sends an AC signal to the TS, and senses the position of the aluminum ring on the beige plastic part. The EPS computer then sends current to the rack motor which causes the torque in the steering shaft to be reduced, which causes the ring to move back toward the neutral position.

Clear as mud?

Jim