VSC alarm, wheel lockup, Looking for solution

[DarkPharf]

I have not seen a satisfying final solution for this issue so I am starting a new post:

Issue: VSC light and alarm on wide sweeping turns just over 30MPH and dangerous VSC brake engagement in dry conditions. I experience this on lower speed (30+) situations like cloverleaf interchanges, also on highway driving (70+) on long mountain curvy roads like I90 through Idaho and Montana. The VSC should not be grabbing this early given the perceived yaw being experienced.

Vehicle: 2001 LX470 @ 200,000 miles with AHC removed and replaced with OME shocks, med. Springs and Heavy T-Bars with 1.5" lift, differential drop. Steel bumpers, roof rack, 18" wheels and 33" tires.

Diagnostics Via Techstream and confirmed by Lexus Dealer (See attached PDF):
1. Checked all wheel speed sensors for normal operating parameters and cleanliness.
2. Checked Steering angle sensor for operability.
3. Checked Yaw sensor for operability.
4. No DTC codes encountered.

Actions so far:
1. Calibration memory reset and Zero Point Calibration of sensors.
2. Test drive with Lexus Master Tech and techstream connected.

Dealership assessment: All systems are functioning as designed. The yaw sensor is picking up a -18 degree pitch over 30mph and begins the VSC warning. At -20 degrees the skid correction begins. He believes the lift and extra weight on the vehicle is causing it to yaw more than factory spec. Theoretical solutions to change the spec that they came up with were to check with Toyota to see if the Landcruiser VSC/ABS ECU module has different spec and would allow more yaw before engaging. And another idea to get rid of VSC altogether is to install the Yaw sensor upside-down so it would send a null value.

I am asking for the collective wisdom of the forum to help build out a good thread that we can put in the FAQ on this topic especially if we find a definitive solution. If the dealer assessment is correct then anyone with a heavier than stock rig should be experiencing this issue. I don't believe that to be the case.

 

[re_guderian]

... And another idea to get rid of VSC altogether is to install the Yaw sensor upside-down so it would send a null value.

Interesting...

#1, can't believe a dealer actually suggested that solution, but it's interesting. Would it trip a dash light?

#2, would the upside down sensor actually send a null value? How is it mounted?

I have only had the issue with the super-soft original Fox shocks. And only on a decreasing-radius, crazy-banked freeway interchange. On my 2000. Definitely disconcerting, but I think the throttle cut mitigates actual crash risk. I had just mentally chalked this up to "ECU programming parameters, and nothing much we could do to fix it." You bring up some good points to ponder...

 

[Lowbudgetlc100]

this happen to my lc and it was a loose sway bar on the left rear. forgot to tighten the bolts.

 

[DarkPharf]

Lowbudget, that is a good point an my next area to check. I had also seen in the threads, reports of a loose shock mount. If the system is working "correctly" , Then I must have something that is allowing the yaw to be out of parameter. So I will go on a suspension system bolt torque crusade this weekend and see if anything is loose.

Also as a follow up on the dealer comments about the sensor. They were at a loss for ideas "by the book", so the suggestions were "off the record" and trying to give me some unique ways to deal with the yaw spec.

 

[Junglejack]

Hard not to wonder if the AHC removal might be somehow the culprit with VSC/ATRAC assumably being calibrated with AHC in the mix. That said, obviously there are many folks here who have not had a similar issue after switching to the conventional suspension.

 

[Lowbudgetlc100]

did this happen after the swap?

 

[PADDO]

The EWD and data I have access to ('03) has interconnections between the suspension ECU and the ABS/BA VSC ECU. The consequences of spurious data - or the absence of valid data - between the two ECU needs to be understood. But JungleJacks point that you're not exactly unique in your ahc delete and build is relevant. You'd think if the absence of data between ecus was the root cause here then there would be other built ex ahc vehicles experiencing the same.

 

[3D FJ]

What happened in the end? I think i'm having a similar problem. Rather than start a new thread, here is an account of my current problem.

For the past few months, I've been driving around with the steering wheel turned to the left (top center of steering wheel at about 10~11 o'clock) Just recently installed my 35's (previously had 33's) and was still driving around for about 400 miles like this. No real problem whatsoever. Truck would track straight, but i knew i needed an alignment before going on much longer. Today, i was bringing the truck to a shop for an alignment. Before i left home, i measured fender to center of hub on the front to make sure that the height was the same or close to the same left to right and made the proper adjustments (right side was a little higher than left in front) I drive about 18 miles to the shop where they put it on the machine and tell me that they can't really adjust my UCA bolts (for toe i'm guessing) without having to first remove my tires (i torqued them to spec according to the FSM when i installed the spc arms). I couldn't wait for them to do that because i needed to pick up my daughter so i told them i'd be back the next available day. They did however make some adjustments and said it should be a bit better but they'd rather complete everything at the next time i was there so it'd be done right. When i pulled away from the shop, the truck didn't drive any different except that the steering wheel was more straight (top center of steering wheel almost at 12 o'clock) I drive home and on the way home, at about 30 mph, the VSC alarm sounded and then went off, and the brake pedal pulsed as if the abs was firing. Then i get on the highway, and at just over 50 mph, the same thing happened but this time the alarm didn't turn off until i pulled over at a rest area. Called the shop and I believe they said they just adjusted the tie rods. Drove the rest of the way home with no issue. I took the truck out again tonight, and the same thing happened.

Can someone point me in the right direction as to what I should be looking for? Any help would be greatly appreciated.

 

[Doctor Koko]

I want to suspect that the tech simply loosened something and then failed to tighten what he loosened (see the third post above: "this happen to my lc and it was a loose sway bar on the left rear. forgot to tighten the bolts."). If it were me I would first climb under and just take a look, shake everything to see if anything is loose and hand check what I could. If I couldn't find a culprit I'd jack up each wheel off the ground and keep at it (grab the tires at 3 and 9 o'clock and 6 and 12 and try to rock them just see if anything doesn't feel right--you could have something that was worn or broken that the ECU didn't notice until they "adjusted things"). You know, I forgot something obvious--the first thing I'd really do is plug in my OBD2 scanner and see if any codes pop up.

One option is taking it back and having them finish the job they wanted to do in the first place and see if this is all still happening, but I think it's a better idea to know what's wrong before you go back. Besides, if you have something that needs to be fixed or replaced you don't want to pay for an alignment and get another one in a week.

 

[3D FJ]

I sure hope someone has additional thoughts. Today, I checked for anything loose that could have been touched at the shop. Nothing seemed loose or out of place. I tried doing that zero point calibration via the paper clip method and I didn't have any luck. I pulled a p0550 code (i'm pretty sure that's what it was) using my ultragauge. There was no check engine light, but when i checked for codes, that's what came up. I cleared that, but it wasn't any help. i don't know of anything else to check. I'm thinking it may be time to go to the stealership.

 

[Doctor Koko]

I'm at work killing time and don't have my shop manual to peruse, but Google says that code is a power steering sensor/switch issue (I've never replaced one of these and have no idea how common or rare this problem is, so I am not the best person to respond right at the moment but will anyway). The dealership will have an advanced scanner (the one that plugs in under the hood) and will likely be able to give you more information specifically. It might be worthwhile to let them scan it and then decide if you want to let them fix it or do it yourself.

Or you could replace that sensor, flush the power steering fluid and see if that resolves things (this is what I would do as I live hours and a mountain pass or two from a dealer). I can look that up in my manual tomorrow and post the part number , but it's probably a better idea to have the dealer scan it and give you a quote.