AHC Sensors Driving Me Crazy!! HELP PLEASE!!!

[Uwiik]

Hi all,

My HDJ101 is taking forever to go from L to N, so I bought new sensors for front R and L, the new sensors fixed my slow raising AHC, now I can raise from L to N in 10 seconds flat, but it comes with its own problem. The problem is, it is extremely difficult to get the R and L readings to agree with each other. Doesn’t matter on what position I first installed the sensors Techstream reading would always show FL with huge positive number (+28mm to +37mm) and FR with extreme negative number (-40mm to -23mm), never ever start with close to each other readings. I ended up installing FL sensor arm on the very top of the slot and FR sensor arm on the very bottom of the slot to get both reading closer to each other, on top of that I also have to extend the FR sensor arm to the max to get FR reading closer to FL. The most frustrating part is after I managed to get the sensors to be within less than 7mm to each other (eg. FL 2.5mm FR -2.5mm) after a short drive or L to N cycle the reading will change itself to totally WAY OFF number (eg. FL -4mm FR -18mm ) and I always run out of adjustment thread after the erroneous change......

I swear I was thinking about pouring gasoline to the damn truck and set it on fire and be done with my problem. This damn truck with the never ending AHC problem really get to my nerve....I managed to fix everything else AHC related and the truck is driving comfortably but I know its not 100% (I have access to my dad’s truck with perfect AHC for comparison), the last piece of the puzzle of my AHC agony is the sensors, if only I can get both front damn sensors to permanently agree with each other.

Below is the screenshot of my latest setup, this screenshot was after I managed to get both sensor at FL 2.5mm FR -2.5mm, took a short drive and the reading changed itself to totally erroneous readings shown below. I really need your help folks, I don’t even mind paying for the tutorial. I have used search button and I couldn’t find any concrete answer to my problem, nobody ever discuss AHC sensor adjustment down to details.

 

[Leandro]

Height sensors are just variable resistors, take them off and check if they are both in range with a multimeter (you can't do this while connected to the truck)
Do you still have the old ones? Use them to compare.
If they check out fine, then you might have a short or other electrical problem in the AHC circuit that is throwing the ECU off.

 

[suprarx7nut]

Is there a chance that the AHC values are correct and the vehicle is shifting height due to an odd suspension problem outside of AHC?

In other words, have you measured from wheel center to fender to verify that the vehicle is remaining level and stable?

 

[Uwiik]

Height sensors are just variable resistors, take them off and check if they are both in range with a multimeter (you can't do this while connected to the truck)
Do you still have the old ones? Use them to compare.
If they check out fine, then you might have a short or other electrical problem in the AHC circuit that is throwing the ECU off.

I also suspected electrical problem, but the AHC was working flawlessly when I bought the truck end of last year. All AHC problem started to show after a stupid workshop replaced front upper/lower arms, tie rod and flushed the AHC fluid screwing up everything, off course when I asked the mechanic he claimed he’s done thousands of Land Cruisers. I had re flushed the AHC oil by Paddo’s method after the incident but perhaps there is still some air trapped in the system? What is the symptom of trapped air in the AHC system? Is my symptom one of that?

 

[Uwiik]

Is there a chance that the AHC values are correct and the vehicle is shifting height due to an odd suspension problem outside of AHC?

In other words, have you measured from wheel center to fender to verify that the vehicle is remaining level and stable?

The vehicle remains level and always settle at the same height, I have no problem maintaining 52cm on rear (center cap to fender lip) but I struggle to have 50cm up front, it’s always either 1-2cm too high or 1-1.5cm too low, never managed to get it exactly at 50cm. I do have DTC C1777 steering angle sensor problem, bought the sensor and going to test and fix tomorrow but I doubt steering angle sensor DTC have anything to do with erroneous sensor reading?

 

[suprarx7nut]

The vehicle remains level and always settle at the same height, I have no problem maintaining 52cm on rear (center cap to fender lip) but I struggle to have 50cm up front, it’s always either 1-2cm too high or 1-1.5cm too low, never managed to get it exactly at 50cm. I do have DTC C1777 steering angle sensor problem, bought the sensor and going to test and fix tomorrow but I doubt steering angle sensor DTC have anything to do with erroneous sensor reading?

I'm not sure I follow.

When the sensor indicates low (-15mm for instance), is that side of the vehicle actually low at all?

 

[Uwiik]

I'm not sure I follow.

When the sensor indicates low (-15mm for instance), is that side of the vehicle actually low at all?

I'm not sure I follow.

When the sensor indicates low (-15mm for instance), is that side of the vehicle actually low at all?

When my FR sensor read -35mm and FL sensor read 25mm the front is sitting lower than specification but level to each other.

 

[suprarx7nut]

Hmm, ok, thanks.

I'd unplug the sensor and check resistance at the sensor and then at the AHC ECU. Ensure you get the same results. That should rule out a wiring fault. I have a 98 LX470 EWD and could screenshot some pages if it helps.

 

[Uwiik]

Hmm, ok, thanks.

I'd unplug the sensor and check resistance at the sensor and then at the AHC ECU. Ensure you get the same results. That should rule out a wiring fault. I have a 98 LX470 EWD and could screenshot some pages if it helps.

Thank you very much for the kind offer, off course I would love to have the screenshots, that would help me a lot. Again, thank you!

 

[Biga27110]

As someone who has removed AHC its so great not to think about this anymore

 

[suprarx7nut]

Well they seem to only call out voltage values while applying 4.5 V. Not the simplest test, but I presume you can't do a simple resistance test.

Once you rig up a little battery holder for 3 AA's and some wire connectors, checking that voltage wouldn't be too bad.

Checking the heights per the method they describe might be helpful. If you're chasing a few mm, it could be really easy to mis-measure with a tape measure going from hub center to fender.

Let me know if that helps at all.

 

[l3n0x]

Are these genuine toyota sensors?

 

[uHu]

I also suspected electrical problem, but the AHC was working flawlessly when I bought the truck end of last year. All AHC problem started to show after a stupid workshop replaced front upper/lower arms, tie rod and flushed the AHC fluid screwing up everything, off course when I asked the mechanic he claimed he’s done thousands of Land Cruisers. I had re flushed the AHC oil by Paddo’s method after the incident but perhaps there is still some air trapped in the system? What is the symptom of trapped air in the AHC system? Is my symptom one of that?

Air or foam or flat spheres doesn't matter. The AHC just increases the pressure until the height is zero, as long as max pressure limit is not reached. If the height signal from the two fronts are too far apart, the ahc will not adjust the height.
The steering signal is an input to the AHC ECU. If the steering signal is more than +/- 30 (or was it 35), the gate valve between left and right side will close to avoid leaning in curves. But only at over a certain (low) speed.
From the symptoms described in this thread, it sounds like you have a sensor problem, either inside a sensor, with the sensor arm/shaft, linkage, bracket, or with the cabling/plugs. Before you take the sensors off for checking, testing and comparing; mark the shaft/arm position when at N height; and measure resistance values at that position. The middle (sliding brush) connector (pin 1 on the fronts, IIRC) should be at about half of the total resistor value at that position. It is important that the resistance changes smoothly and consistently over the whole working range. That is easiest to check with an old analogue meter where you can actually see the smooth movement of the needle, and not some jumping digits

 

[Biga27110]

Well they seem to only call out voltage values while applying 4.5 V. Not the simplest test, but I presume you can't do a simple resistance test.

View attachment 2240705
View attachment 2240706
View attachment 2240707
View attachment 2240708
View attachment 2240709

Once you rig up a little battery holder for 3 AA's and some wire connectors, checking that voltage wouldn't be too bad.

Checking the heights per the method they describe might be helpful. If you're chasing a few mm, it could be really easy to mis-measure with a tape measure going from hub center to fender.

Let me know if that helps at all.

I love the support from this community.

 

[Portertg]

I replaced my front AHC sensors because one actually froze in place, the other had the typical fault of corrosion on the springs. I replaced both with aftermarket sensors, from Amazon. I had good results right away but then it started acting up again. I charted the height readings and found the FR to be very noisy, on a straight and level road it would go positive and then negative, and back. It was a mess. So i replaced that one again, again with a cheap aftermarket sensor. it worked great. Until it snowed, then it was trash again. I popped the lid off of it and found some fluid in it. I'd verify that your sensors are clean and dry on the inside.
I have a couple of the dorman replacements on the way.
as i understand the AHC ECU, it takes the FR and FL height sensors and adds them, then uses that value to correct to height. if you have a cross level issue, then the TBars need adjustment.

 

[Uwiik]

Well they seem to only call out voltage values while applying 4.5 V. Not the simplest test, but I presume you can't do a simple resistance test.

View attachment 2240705
View attachment 2240706
View attachment 2240707
View attachment 2240708
View attachment 2240709

Once you rig up a little battery holder for 3 AA's and some wire connectors, checking that voltage wouldn't be too bad.

Checking the heights per the method they describe might be helpful. If you're chasing a few mm, it could be really easy to mis-measure with a tape measure going from hub center to fender.

Let me know if that helps at all.

Thanks for the screenshot, much appreciated .... I did the test and everything seems normal, left and right reads consistently the same.
At this point I highly suspecting either the AHC ECU itself or broken/shorting/intermittent wire on the harness. I tried to replace my steering angle sensor today and my DTC C1777 remains, meaning I have a fault somewhere up the line, not on the steering angle sensor itself. This should explain why I can never set my FR/FL Height sensor to remain consistent, even today I also realized that my RR sensor is also all over the place. I think all of my AHC problem is because the ECU is producing/getting erroneous signals. The good news is even with the erroneous sensors reading I was able to get all three height sensors to be at least close to each other (despite the constant self change), after hours of constant swearing and self loathing now the physical position of the sensors on the bracket + adjustable bolts are totally whacky but it’s working, I had to use the height offset feature on Techstream to make my setup works. Now my truck is riding really comfortable again and I have perfect 52 cm rear and 50cm front height (center of hub to fender lip) and equal physical height between R and L but I know I have a task on hand to fix.
If it’s not too much of a problem, can I get the part of the manual for analyzing the AHC wiring harness and the AHC ECU itself? I have complete 2004 FSM on PDF but it’s the widely available PDF file which everyone’s having where there is no AHC section on the manual.

Again thank you very much to you guys all for all the help!!

 

[Sargy]

Hopefully the technician that worked on your front lower control arm RR placed the torsion bars back where they are and didn't touch the adjusting nut.

Glad you got it sorted.

 

[Uwiik]

Hopefully the technician that worked on your front lower control arm RR placed the torsion bars back where they are and didn't touch the adjusting nut.

Glad you got it sorted.

That was 3 months ago. I have torn apart and re fit everything back to specifications. Followed the “definitive list of AHC maintenance items” thread religiously and also by using my own logic I was able to set everything nicely. It is crazy how much mess a mechanic with no idea can do to AHC system.

 

[suprarx7nut]

Thanks for the screenshot, much appreciated .... I did the test and everything seems normal, left and right reads consistently the same.
At this point I highly suspecting either the AHC ECU itself or broken/shorting/intermittent wire on the harness. I tried to replace my steering angle sensor today and my DTC C1777 remains, meaning I have a fault somewhere up the line, not on the steering angle sensor itself. This should explain why I can never set my FR/FL Height sensor to remain consistent, even today I also realized that my RR sensor is also all over the place. I think all of my AHC problem is because the ECU is producing/getting erroneous signals. The good news is even with the erroneous sensors reading I was able to get all three height sensors to be at least close to each other (despite the constant self change), after hours of constant swearing and self loathing now the physical position of the sensors on the bracket + adjustable bolts are totally whacky but it’s working, I had to use the height offset feature on Techstream to make my setup works. Now my truck is riding really comfortable again and I have perfect 52 cm rear and 50cm front height (center of hub to fender lip) and equal physical height between R and L but I know I have a task on hand to fix.
If it’s not too much of a problem, can I get the part of the manual for analyzing the AHC wiring harness and the AHC ECU itself? I have complete 2004 FSM on PDF but it’s the widely available PDF file which everyone’s having where there is no AHC section on the manual.

Again thank you very much to you guys all for all the help!!

Like this?

 

[95Fantasma80]

As someone who has removed AHC its so great not to think about this anymore

I'm sorry for your loss, it's such a great system when properly maintained.