AHC Front leveling control valve testing

[84bj60]

Good evening,

I write this while covered in gravel, mud and road grime. I have pulled every hair out off my head and every connector apart that I can find including BI1 BI2 BI3, found 2 very lightly corroded connections on accumulator wiring but not my issue.

I replaced the pressure transducer on the pump last week.

Truck is currently throwing a 32 code. (front levelling control valve solenoid circuit). Flashing off light, stuck in low.

2002 LX470 (build date 2001 09 month) LHD

Can someone please provide me with the correct testing sheets from the FSM for my rig to test the wiring from the BI connectors to help me narrow down my assumed wiring harness problem. I have an aptitude for electrical troubleshooting, I just need to know what pins to test and what the resistance/voltage should be.

I have not dug into the ECU yet.

Any help would be greatly appreciated.

 

[84bj60]

Hey guys,

I have had the LX in the garage since Friday night trying to figure this out, my wife needs to take the kids to school tomorrow morning; it snowed a foot yesterday here, Hoping to get this thing fixed today.

Anyone out there have a source for the FSM testing procedures for code 32?

Thanks in advance.

 

[84bj60]

Uodate, I have tested the control valve connector from the common terminal to each of the 4 solenoid pins on the control valve itself. 3.5 ohms on each, leads me to believe all solenoids are OK. when I meter back towards the ECU from the connector I get 45kohm on each from common except one wire, the black with yellow stripe, I will work it back from here and see where my broken wire is, hoping for just a broken wire at this point!

 

[84bj60]

Got it... Black yellow wire was broken between BI1 and the levelling valve bank. there is another connector to test between BI1 and the valve bank but it looks to be near impossible to get at between the frame and the boat above the suspension brackets. I cut the wire coming out of each connector and put a new wire in for now. will dig into that in the summer.

Thanks to all who posted in other threads, I was able to scrounge up enough EWD's and connector locations to figure it out...

Would be nice if there was a locked thread that had all of the target resistances for each component of the AHC listed for component testing.

 

[suprarx7nut]

Got it... Black yellow wire was broken between BI1 and the levelling valve bank. there is another connector to test between BI1 and the valve bank but it looks to be near impossible to get at between the frame and the boat above the suspension brackets. I cut the wire coming out of each connector and put a new wire in for now. will dig into that in the summer.

Thanks to all who posted in other threads, I was able to scrounge up enough EWD's and connector locations to figure it out...

Would be nice if there was a locked thread that had all of the target resistances for each component of the AHC listed for component testing.

Sounds like you found another example where the wire harness is damaged between BI1 and that valve block area. That's at least 4 I know of. In none of the cases were people able to figure out where the actual damage was, but it would be great to figure that out!

 

[84bj60]

If I had the time I would find it, mostly to find the other 4 wires that will probably be close to failing... I ran a 5 conductor cable in case the others fail (common and 4 solenoid signals)

I defiantly feel better now knowing the system wiring! I will be ordering a tech stream cable so I can really dig into the rest of the system.

I find it crazy the whole system shuts down and goes to low sports mode due to 1 open circuit! sure would be easier to troubleshoot if one corner didn't go up!

 

[franknstein]

Sorry to revive an old thread, but I wanted to chime in about this. I wound up having the same problem in my 2002 LX470, wires 4 and 5 out of the height control valve block assembly were broken, which was ultimately the only problem I had. Symptoms were as follows:

It started with an intermittent blinking AHC off light, shortly followed by the rear rising but front struggling to do so, then locking out into fail safe mode. I didn't have techstream yet, so I may have missed some data early on, but it showed 0.0 pressure readings all around and 1763 abnormal oil pressure and another code I can't remember at the moment.

Being new to AHC, as I'm a pretty new owner, I was looking into all sorts of things and it was in a mechanic's shop for two weeks just for them to say "uh, I don't know, I never work on these, I give up. But I think it's the height control valve." After the mechanic cleared codes a bunch of times and messed around with it, it ended up showing rear pressure at like 19mPa, waaay too high, while the front and accumulator were still 0.0. I figured this means that the ECU stopped recording after it saw the rear pressure being so high as a result of all the mularky and a dead-head front solenoid valve, and went fail safe before reading front pressures.
I had had a full flush and new globes about a week prior to the light coming on, which I thought maybe had caused a blockage in the valve from loosened debris but wanted to bench test it (on the vehicle), so first I tested continuity of the wires leading to the AHC ECU, which I mentioned were broken, so I bypassed them and it worked. I would have put voltage to the terminals on the valve block had that not been it and listened for the solenoid to click, but no need. Turns out the globes were a red herring. I do plan on cleaning my screens when it's a bit warmer out as I don't have a garage, but back to normal for now.

In short, everyone locally will tell you that you should just rip out the AHC and put in a new/inferior in many ways conventional suspension, but the AHC is sweet and while it's kind of complicated, it's not actually that complicated. Read the FSM, meaning not just the parts you think you need to look at but the overall description of the system and the sum of its parts, think about the system logically, figure out what clues you've got. I had abnormally high oil pressure and the indication that only half my system was receiving pressure which brought me to the leveling valve. I'm no computer engineer but I'm guessing the Toyota guys are pretty logical about it so it all made sense in the end. Thanks to everyone else who posted theie solutions, hopefully this pays it forward to someone.