(SOLVED) A unique LX470 AHC issue: Ignition? (1 Viewer)

[jaewastooshort]

I had actually found a(nother) 6S5 (light green, same code as mine, but tan interior) LX locally with a collapsed suspension and was really hoping to pick it up cheap but the dealership would not respond to me. Figure if I can find one with a trashed AHC system I might get a deal since I already have a static kit to convert and I'm not yet sold on removing AHC from my own daily. Waiting on my own cable to arrive so I can finally get my front back into spec.

Hope techstream helps get your issue sorted

 

[BW100]

After getting Techstream up and going this afternoon, I was able to get the following data on the AHC system. This was done with the temp sensor unplugged. I haven’t received the replacement AHC switch yet, so I am not able to rule that out as a contributor. Regardless, it appears I at least have an issue with the rear height sensor, as well as the front speed sensors.
Before I connected to Techstream, I cross leveled the torsion bars, as my passenger side was 1/4” higher. I lowered it to match the drivers side. I was going about this in the same method described in “ABCs of AHC”, even though I clearly have some sensor issues.
I’m open to advice on how to proceed from here; ie, if it’s worth trying to make sensor adjustments at this point, OR,

cleaning sensors and hoping that helps; or should I begin with replacing the malfunctioning sensors.

 

[suprarx7nut]

After getting Techstream up and going this afternoon, I was able to get the following data on the AHC system. This was done with the temp sensor unplugged. I haven’t received the replacement AHC switch yet, so I am not able to rule that out as a contributor. Regardless, it appears I at least have an issue with the rear height sensor, as well as the front speed sensors.
Before I connected to Techstream, I cross leveled the torsion bars, as my passenger side was 1/4” higher. I lowered it to match the drivers side. I was going about this in the same method described in “ABCs of AHC”, even though I clearly have some sensor issues.
I’m open to advice on how to proceed from here; ie, if it’s worth trying to make sensor adjustments at this point, OR, View attachment 3710693cleaning sensors and hoping that helps; or should I begin with replacing the malfunctioning sensors. View attachment 3710694

Personally, I would measure the sensors and see if they are ok. I don't recall if that's a simple resistance (Ohm) measurement or if it's spec'd by voltage only (meaning you'd need to test with the car on and connectors connected).

That front wheel speed sensor is a strange fault. Makes me wonder if you have a wiring issue.

I would chase down a wiring manual and see if you can check the speed sensor circuit anywhere. Step 1 for me is to figure out if you have a component problem or a circuit problem.

 

[LJE]

Personally, I would measure the sensors and see if they are ok. I don't recall if that's a simple resistance (Ohm) measurement or if it's spec'd by voltage only (meaning you'd need to test with the car on and connectors connected).

That front wheel speed sensor is a strange fault. Makes me wonder if you have a wiring issue.

I would chase down a wiring manual and see if you can check the speed sensor circuit anywhere. Step 1 for me is to figure out if you have a component problem or a circuit problem.

You can test the height sensors with just a multimeter - they're just a potentiometer. @PADDO explains how here: High as a kite, hard as a rock! (Yes AHC again...) - https://forum.ih8mud.com/threads/high-as-a-kite-hard-as-a-rock-yes-ahc-again.1119157/#post-12149330

 

[BW100]

Personally, I would measure the sensors and see if they are ok. I don't recall if that's a simple resistance (Ohm) measurement or if it's spec'd by voltage only (meaning you'd need to test with the car on and connectors connected).

That front wheel speed sensor is a strange fault. Makes me wonder if you have a wiring issue.

I would chase down a wiring manual and see if you can check the speed sensor circuit anywhere. Step 1 for me is to figure out if you have a component problem or a circuit problem.

I can confirm that the front left speed sensor is inop. Driving around the driveway hooked to Techstream showed speed on the right wheel sensor, and no movement on the left. This also apparently correlates to the ABS, VSC Off / Trac Off lights on the dash. I read several other posts stating those lights were triggered by a faulty speed sensor. (Techstream didn’t identify any issues specific to ABS either)
Whether or not the speed sensor has anything to do with the AHC not working correctly - that’s yet to be determined. I suspect the rear height sensor is completely gone. Adjustment of the linkage produced no change in the numbers in Techstream.

I discovered all of your previous write ups about tuning the AHC system, along with the YouTube video. Very informative, and very much appreciated.

 

[suprarx7nut]

I can confirm that the front left speed sensor is inop. Driving around the driveway hooked to Techstream showed speed on the right wheel sensor, and no movement on the left. This also apparently correlates to the ABS, VSC Off / Trac Off lights on the dash. I read several other posts stating those lights were triggered by a faulty speed sensor. (Techstream didn’t identify any issues specific to ABS either)
Whether or not the speed sensor has anything to do with the AHC not working correctly - that’s yet to be determined. I suspect the rear height sensor is completely gone. Adjustment of the linkage produced no change in the numbers in Techstream.

I discovered all of your previous write ups about tuning the AHC system, along with the YouTube video. Very informative, and very much appreciated.

You do not know if the components are bad, or if just their wiring is bad.

AHC is speed dependent. If the speed sensor (or its wiring) is bad, your AHC will not work as intended.

 

[BW100]

You do not know if the components are bad, or if just their wiring is bad.

AHC is speed dependent. If the speed sensor (or its wiring) is bad, your AHC will not work as intended.

Either way, it sounds like the lack of feedback from the front left wheel speed sensor is causing some sort of fault in the AHC. From what I was reading in a separate post about speed sensors, they tend to kick on the warning lights for ABS, TRAC OFF, and VSC OFF when the sensor or wiring goes bad.

Loosening and sliding the rear height control adjustment had no effect on the live numbers in Techstream, either.

 

[BW100]

UPDATE: Here is what fixed my AHC issue. Techstream revealed that I had a malfunctioning rear height sensor, as well as a non-working front left wheel speed sensor. I ordered replacements for both of these, but wanted to install and test with each individually to see if one in particular was affecting the AHC system. I also picked up a confirmed-working replacement console switch, just in case.

I replaced the switch first. No change there.

I then replaced the rear height sensor next. I eyeball adjusted it to roughly where the old one was set, and just like that, the AHC system was fully functional again. High, Normal, and Low were now all working as intended. I then spent the next several hours performing all of the torsion bar and height sensor adjustments to get everything back within the normal parameters. And just like that, AHC was fixed. No longer did I get the height increase when starting the ignition, nor did I get the drop in height when turning the key to ON. That all just ceased to exist.

Although it now seemed that the non-functional front left wheel speed sensor was having no effect on the AHC system, the ABS light was still activated from the fault code. So lastly I replaced this wheel speed sensor, and then cleared the ABS code. I can’t say for sure that it was having any ill effect on the vehicle prior to replacement, but, I can confirm the new one is working, and the ABS light has been off for the last 4 weeks now.

I then installed the new tires, and went in for an alignment. I explained to the alignment tech what my old tires looked like, and what my theory was as to why they were wearing so badly, and so quickly, on the outer treads. After reading all of the “before” numbers, it was easy to see that the truck (at Normal height) really wasn’t out of alignment at all. There was very little adjustment to be made, which confirmed my theory: that with all of the random height increases caused by the ignition, that most of the time the truck was higher than the height in which it was aligned at. Therefore for the majority of the time, the suspension was in a positive camber position, which resulted in the accelerated outer tread wear.

I appreciate all of the advice, as well as the help getting started with Techstream. It is every bit as invaluable as everyone stated it to be.