My steering wheel is off slightly to the left when the wheels are straight. Can any alignment shop fix, and does this impact the AHC system during cornering as far as body roll is concerned?
Steering wheel alignment (1 Viewer)
- Thread starter Drogon
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If you're happy with the vehicles tracking, it doesn't pull, no uneven tire wear etc yet the steering wheel is slightly off center then this is correctable with small, equal and opposite adjustments to your tie rod ends. Any alignment shop can do this. Don't let the shop adjust total vehicle height by adjusting TBs - it doesn't work that way for AHC.
Regarding your question "does it impact the AHC system during cornering as far as body roll is concerned?" Technically yes, it does but practically it probably isn't affecting body roll too much if it's just a small steering wheel misalignment. Here's what I know. The steering angle sensor (SAS) provides an input to the AHC ecu, this input value increases positively in one direction, goes through a zero null and increases negatively in the other direction. The AHC ecu will activate the gate valves (FG and RG in techstreams AHC data list) to hydraulically isolate the left/right front and left/right rear shock actuators to stiffen things up during a turn based on SAS input and speed. For normal straight line driving (SAS input ideally 0) both side shock actuators are connected in parallel and for slight turns with little roll a small amount of fluid from the lower corner/side will transfer to the higher side - like water sloshing back and forth in a bucket if you will - and then it settles down when you straighten up. Now the gate valves act as hydraulic partitions in the bucket to stop the sloshing (roll) when necessary. @uHu and I've swapped messages and done some techstream testing and @uHu found that he could observe his FG valve operating as a function of steering wheel input and vehicle speed and the actuation point was based on his SAS null point, as you'd expect. At the time his SAS null (0) wasn't exactly aligned with his front wheels pointing straight ahead - and he observed an offset between left and right cornering and FG operating. So there is the answer, yes if the SAS null isn't zero and perfectly correlated with the front wheels physically pointing straight ahead it alters the left and right turn operating point of FG and therefore influences the way the system manages body roll. Now my own observations and testing confirm that FG and RG operate as a function of SAS and speed too. I've hooked up techstream and graphically displayed steering angle, vehicle speed, FG and RG and observed (with playback recording fwiw) what's going on as you corner, accelerate etc. Unfortunately I was doing this solo and there is a point where you think twice about throwing your vehicle around the streets whilst watching the laptop in the passenger seat. There are limits to what you should do for your own edification. Anyway, I was surprised in that I needed to be a bit more aggressive than expected to get the gate valves to actuate and that for steady, sweeping turns at 30-40 mph they didn't operate. Tighter turns taken at a rate faster than most would normally drive they actuated. Could I tell the difference in handling between when they actuated and not - no. But my testing was limited to <50mph. It would be interesting to attack a winding mountain road and observe the gate valve operating points and try and correlate them to handling and body roll. The AHC literature states something like "gate valves operate at 35 degrees steering input" we'll both @uHu and I've established that vehicle speed is definitely an input, at low speed with full steering lock on they don't operate. If you're doing 75 I bet they operate at much lesser of steering input. HTH
Regarding your question "does it impact the AHC system during cornering as far as body roll is concerned?" Technically yes, it does but practically it probably isn't affecting body roll too much if it's just a small steering wheel misalignment. Here's what I know. The steering angle sensor (SAS) provides an input to the AHC ecu, this input value increases positively in one direction, goes through a zero null and increases negatively in the other direction. The AHC ecu will activate the gate valves (FG and RG in techstreams AHC data list) to hydraulically isolate the left/right front and left/right rear shock actuators to stiffen things up during a turn based on SAS input and speed. For normal straight line driving (SAS input ideally 0) both side shock actuators are connected in parallel and for slight turns with little roll a small amount of fluid from the lower corner/side will transfer to the higher side - like water sloshing back and forth in a bucket if you will - and then it settles down when you straighten up. Now the gate valves act as hydraulic partitions in the bucket to stop the sloshing (roll) when necessary. @uHu and I've swapped messages and done some techstream testing and @uHu found that he could observe his FG valve operating as a function of steering wheel input and vehicle speed and the actuation point was based on his SAS null point, as you'd expect. At the time his SAS null (0) wasn't exactly aligned with his front wheels pointing straight ahead - and he observed an offset between left and right cornering and FG operating. So there is the answer, yes if the SAS null isn't zero and perfectly correlated with the front wheels physically pointing straight ahead it alters the left and right turn operating point of FG and therefore influences the way the system manages body roll. Now my own observations and testing confirm that FG and RG operate as a function of SAS and speed too. I've hooked up techstream and graphically displayed steering angle, vehicle speed, FG and RG and observed (with playback recording fwiw) what's going on as you corner, accelerate etc. Unfortunately I was doing this solo and there is a point where you think twice about throwing your vehicle around the streets whilst watching the laptop in the passenger seat. There are limits to what you should do for your own edification. Anyway, I was surprised in that I needed to be a bit more aggressive than expected to get the gate valves to actuate and that for steady, sweeping turns at 30-40 mph they didn't operate. Tighter turns taken at a rate faster than most would normally drive they actuated. Could I tell the difference in handling between when they actuated and not - no. But my testing was limited to <50mph. It would be interesting to attack a winding mountain road and observe the gate valve operating points and try and correlate them to handling and body roll. The AHC literature states something like "gate valves operate at 35 degrees steering input" we'll both @uHu and I've established that vehicle speed is definitely an input, at low speed with full steering lock on they don't operate. If you're doing 75 I bet they operate at much lesser of steering input. HTH
- Thread starter
- #3
Thank you for the detailed answer, and additional input. I will have a shop look at adjusting the tie rod ends.
Will I need to make any adjustments to the steering sensor to ensure it is at zero when the wheels are straight? I'm assuming I need techstream to check this...
You'll need Techstream to read your SAS output. I've got vgrs which has a different initialization and zeroing procedure so I'm not familiar with how this is done on your pre 03 vehicle.
That was a very interesting read, I hadn't previously thought about how the AHC interfaced with other systems on the vehicle. After reading that I also am now thinking that I need to have my steering (and VGRS) adjusted and tuned by someone who knows what they are doing. My steering wheel has been off for a few months and at one point I did pull the steering wheel to turn it ~15*. It stayed centered for a few weeks but is now off again to the same tune as it was before I pulled the steering wheel.
I haven't noticed any adverse affects to my tires but really am not that great about consistently checking for it. I had been thinking that I should have the alignment done and have the VGRS diagnosed by a real shop for a little bit now but have been afraid to do so since I've read how much the VGRS system costs to replace. There really isn't that much info on VGRS here or online so its been hard to figure out how to go about diagnosing whether the system is just out of parameter or whether it has failed and needs to be replaced. I've gone through a few waves of internet searching since November and most recently checked earlier this week. I found plenty of russian videos but they are of no use to me.
I haven't noticed any adverse affects to my tires but really am not that great about consistently checking for it. I had been thinking that I should have the alignment done and have the VGRS diagnosed by a real shop for a little bit now but have been afraid to do so since I've read how much the VGRS system costs to replace. There really isn't that much info on VGRS here or online so its been hard to figure out how to go about diagnosing whether the system is just out of parameter or whether it has failed and needs to be replaced. I've gone through a few waves of internet searching since November and most recently checked earlier this week. I found plenty of russian videos but they are of no use to me.
You can make this adjustment using Techstream to recenter the wheel, you could also disconnect the battery long enough for the VGRS system to recalibrate.
VGRS light
VGRS light
Recalibration and recentering the steering wheel with vgrs is very simple, less than 5 minute job. I've done it many times.
Recalibration by battery disconnect doesn't always recentre the wheel perfectly, I've tried. After a recal I run the vgrs wizard to unlock the vgrs actuator, recentre the steering wheel thenlet it do its 5 second reinitialization
- Thread starter
- #9
So if I disconnect the battery this might straightenjoy the steering wheel without having to adjust the tie rods? I'm assuming by doing this it would also reset my ahc sensors etc...Other than loosing my radio and memory seat presets, is there any other risks in trying this? Probably a silly question 
You shouldn't lose your radio presets.
I think you're getting a bit confused between non VGRS and VGRS systems. I can't help you with the "old" system. With VGRS the steering wheel is recentered by unlocking the steering actuator, correcting the angular error, then relocking the actuator. This is ideally done using the techstream VGRS wizard and it takes just a few minutes. It can also be done manually by shorting pins, depowering/repowering -pita stuff but still doable. The steering angle valid flag (for VGRS trucks) is reset by pulling battery power for a while then driving straight at +22mph for more than 5 secs, if the steering wheel is still a little bit off center then you need to redo the actuator unlock/center/relocking procedure.So if I disconnect the battery this might straightenjoy the steering wheel without having to adjust the tie rods? I'm assuming by doing this it would also reset my ahc sensors etc...Other than loosing my radio and memory seat presets, is there any other risks in trying this? Probably a silly question
where is this wizard located in techstream settings? i must be missing it. my cable is the older 1.4.1 firmware, could that be an issue (I have a new firmware cable on the way)
my wheel is off left about 15% , but the truck drifts right while on the road. i know i need an alignment, but waiting until i get my sensor lift completed. i'm thinking the alignment will fix the drift, but the wheel will still need to be ccorrected.
techstream currently has my steering angle at 1151. not sure where else to look for data.
In the System Selection Menu (with the yellow horizontal ecu tabs) there is one tab labeled VGRS, select it then choose Utilities from the blue vertical menu and then just follow the prompts. I doubt it's the x horse driver, I'm using 1.4.6 with a Version 7.3xx techstream. Rezeroing the wheel and initializing VGRS then going for a drive to allow itself to validate should correct that 1151 angle.
The book says the expected range is something like +1150 to -1150 so I'm calling 0 as the target value. Getting it set to 0 is quite achievable.
I had a similar issue few weeks back. First took it to Break Check to for an alignment ($139.88 life time alignment) and they tried their best to get it straight with no luck. Lexus Dealer fixed it for $32.95. My advice, take it to the dealer.
Confused! Why take it to a dealer for such a simple and routine item as realigning the steering wheel? - unless you don't have Techstream - @cwininger already said it worked like a charm. I too have lifetime alignment and quickly learnt years ago that non dealers (in my area at least) can't correct VGRS steering wheel misalignments, they simply don't know about it. It's a 5 minute job with four or five mouse clicks to re enter the steering wheel after an alignment or to periodically correct a slight drift in the wheel centering. FSM also calls for the VGRS to be recalibrated after any work in the front end or an alignment. But if taking it to the dealer is your only option then I guess that's what you've got to do.
