AHC Help, Tech Stream Data Review

[ehrgeiz]

Hello,

I was hoping some of the AHC pros could be help me diagnose an issue. I have a 2000 Lexus LX470 Canadian model. I have a Rhino Rack, Columbus Variant RTT and a Alucab Shadow Awning mounted as well as a sleeping platform in the back. Not really much extra weight, maybe 250 lbs.

The story goes... about 1 month ago I had some noise in the front suspension. I dropped it off with my mechanic (not Lexus) to check it out and isolate it. The mechanic advised it was my sway bar bushing. He replaced the bushings.

I took a trip from Alberta to BC about 3 weeks ago for holidays. Had a Jumping Jack trailer on the hitch (light), but the LX was loaded up pretty good with coolers and kids etc. No real issues to speak of though. I noticed the AHC in L a couple of times, but would readjust to N.

About a 2 weeks ago, I noticed another annoying squeak in the front suspension. I dropped it off with the mechanic again who isolated it to the front right shock bushing. The penetrating oil made the noise go away so I figured I would leave it for now and see if it came back before replacing the bushing.

When I went to pick up the vehicle I hopped into the truck fired it up and noticed that the AHC was Off on the dash. I then noticed that the front was raked up high and the rear was low. Upon driving it was incredibly bouncy. Would not go into L or H. I limped it home and called the mechanic the next day inquiring as to if he maybe knocked the height sensor or used the AHC while the vehicle was suspended. He says nay.

I decided to bleed the system out and replace the AHC fluid. The fluid was very dark and I definitely saw some air bubbles. So much so I wasn't content with the single flush and did a second one earlier this week. On the second flush the fluid looked clean (pink-ish) with few air bubbles. I also popped off the right height sensor to see if I could examine any damage, or corrosion looked clean and perfect inside. I put it back on.

The system re-pressurized, but was still high in the front and a little bit bouncy, but not as bad. All my reading on similar issue threads lead me to believe that I needed a Tech Stream to figure WTF was up. Ordered up the cable and booted up the tech stream.

Here is the first data (remember I couldn't get from N to L). Pretty big delta on the FRH and FLH sensors. No trouble codes at all.

For giggles I moved the FRH sensor to the highest point in the bracket (did not change the adjuster but though). Here is the result on the TS.

Okay I pushed the AHC into low and drove a bit very slowly around the neighbourhood and it dropped into L. I connected the TS, then pushed N. Nothing happened, just a blinking light. Went for a drive and the system pushed into N. See below for the result in TS data. The MPA is really, really high. PS I pulled the temp sensor as recommended for pressure checks which produced the error code. Data for this posted in the below reply.


So, I'm inclined to start ratching up the torsion bars to try to reduce the MPA in the front system, but the rear is high too. I'm not really sure what to make of all this. I don't have super heavy bumpers or anything like that. With the pressures being so high is it fair to say that the pump and globes are good? I wonder if the height sensors are pooched and that's throwing everything out of order. Maybe my mechanic unknowingly reset the torsion bars when changing the sway bar bushing? Not really sure what to make of it all. Any thoughts or insight are very welcome!

Thanks in advance,

Dave

 

[ehrgeiz]

 

[GTV]

Gotta get those pressures in spec. Start here:

The ABCs of AHC - How to Measure, Flush, and Adjust all in one place

I initially put this in the Definitive list of AHC maintenance items thread, but at almost 800 posts long and growing, it's going to get buried and the thread itself is very unwieldy. In an attempt to make as focused a summary as possible, I present "The ABCs of AHC." It's intended as a...

forum.ih8mud.com

 

[ehrgeiz]

Gotta get those pressures in spec. Start here:

The ABCs of AHC - How to Measure, Flush, and Adjust all in one place

I initially put this in the Definitive list of AHC maintenance items thread, but at almost 800 posts long and growing, it's going to get buried and the thread itself is very unwieldy. In an attempt to make as focused a summary as possible, I present "The ABCs of AHC." It's intended as a...

forum.ih8mud.com

Roger!

Okay, 11x turns clockwise on the torsion bars and MPA is high 7's on front and back with me in the drivers seat. Not sure how many more tuns the torsion bar will go, getting pretty stiff!

Also, got the height sensors closer together, but not enough thread or brackets to bridge the gap. Still a sizable delta, but the system is working, goes up, goes down on command. The height sensors definitely seem shot. I'm going to order new FR and FL sensors. I see Amazon has a brand for cheap "A-Premium". AISIN has some on Rock Auto for a lot more coin. As I understand it these sensors are very simple, I'm thinking go cheap for such a basic sensor arm.

Also, have about 9 graduations between H and L. So guess the globes are still passable for now. Date on them bulb is 2000 so factory original. 22+ years service is pretty decent.

Ordered a Slee 30mm spacer for the rear springs too. When I've got the cooler, gear and trailer on hitch I figure I'm pushing the rear pressures so might be wise to reduce them a touch with spacer.

I must say that Tech Stream is the tits. Sure makes this all a lot easier!

Will report back with outcome for anyone else reading/ diagnosing AHC issues.

 

[GTV]

Roger!

Okay, 11x turns clockwise on the torsion bars and MPA is high 7's on front and back with me in the drivers seat. Not sure how many more tuns the torsion bar will go, getting pretty stiff!

Also, got the height sensors closer together, but not enough thread or brackets to bridge the gap. Still a sizable delta, but the system is working, goes up, goes down on command. The height sensors definitely seem shot. I'm going to order new FR and FL sensors. I see Amazon has a brand for cheap "A-Premium". AISIN has some on Rock Auto for a lot more coin. As I understand it these sensors are very simple, I'm thinking go cheap for such a basic sensor arm.

Also, have about 9 graduations between H and L. So guess the globes are still passable for now. Date on them bulb is 2000 so factory original. 22+ years service is pretty decent.

Ordered a Slee 30mm spacer for the rear springs too. When I've got the cooler, gear and trailer on hitch I figure I'm pushing the rear pressures so might be wise to reduce them a touch with spacer.

I must say that Tech Stream is the tits. Sure makes this all a lot easier!

Will report back with outcome for anyone else reading/ diagnosing AHC issues.

Great start! Yes, Techstream is essential, especially if you have AHC.

You may need to reindex the torsion bars if you run out of adjustment:

For those with torsion bar questions

Torsion bars 101 FOR NON AHC VEHICLES First some terms so the search function picks this up: - help with torsion bars - how to adjust torsion bars - reindex torsion bars This all went in Amy's thread but I thought those who weren't subscribes may like to see it. Ok lets try get to the...

forum.ih8mud.com

I would source some good used sensors off the classifieds here before I trusted anything off Amazon. Get a spare set as well, faulty sensors can make you pull your hair out.

30mm spacers are always a good idea, depending on your use/pressure readings you may need to step the coils up as well to some King's. Aim to get your pressures on the lower end of spec so you'll still be in the ballpark when loaded up. I also feel like this gives better ride quality and extends component life.

 

[uHu]

When you see that disparity between left and right height sensors' values in TechStream, the first thing to do is to fix that. There is something very wrong with the signal from that right sensor, either the sensor itself, the linkage or the connection/cable/plugs.
I would do a brief visual check of the cables into the plug at the sensor and at the top of the fender (under the hood, next to the plug for the abs sensor), and of the linkage and sensor arm position (comparing with the right). If all that checks out, take off the sensor and measure it with a multimeter. There are tons of info on "how to" in multiple threads in here.

PS: When the difference between left and right sensor becomes too big, the AHC system will stop working.

 

[ehrgeiz]

When you see that disparity between left and right height sensors' values in TechStream, the first thing to do is to fix that. There is something very wrong with the signal from that right sensor, either the sensor itself, the linkage or the connection/cable/plugs.
I would do a brief visual check of the cables into the plug at the sensor and at the top of the fender (under the hood, next to the plug for the abs sensor), and of the linkage and sensor arm position (comparing with the right). If all that checks out, take off the sensor and measure it with a multimeter. There are tons of info on "how to" in multiple threads in here.

PS: When the difference between left and right sensor becomes too big, the AHC system will stop working.

Thanks for the additional info! Yeah I figured I would leave the torsion bars for now as the pressure are high, but not as crazy. Fix the sensors and see where we land. Upon further reading it sounds like those amazon sensors fail readily so I ordered the Aisin units from Rock Auto. I'll swap them in see what happens. I previously pulled off and inspected the FR sensor and everything looked dandy. I should have pulled out the multi-meter and checked the range, but did not.

I also looked at all of the wiring from the sensors and so nothing unusual externally. I didn't open each connector and check the actual pins though. I will report back what happens with the new sensors once installed and then reassess pressures.

Thanks again for the input and instructions. This forum is such an excellent resource and information cache and with unique AHC you just can't rely on a regular mechanic to understand it. The system is actually very simple to work on, but you need to do the requisite reading and have a Tech Stream.

 

[GTV]

The system is actually very simple to work on, but you need to do the requisite reading and have a Tech Stream.

Nailed it.

 

[FxFormat]

I had similar issue to yours after replacing a shock, but my entire truck was on bumpstops and I couldn’t get it to raise, just a blinking light. Hooked up a scanner and the accumulator pressure was zero. Looks like yours is reading zero as well.

To fix my issue, I bled the truck and cycled the pump on and off several times.

First I had the truck off, then turn the truck on and raise it to N. You’ll hear the pump running but nothing was happening, count to 20 and then press the AHC off button and wait 20 seconds, then press the off button again to turn it on. Keep your hood open and put a fan to the pump if you can go help keep it cool. I had to do that maybe 6 cycles and then truck finall my built pressure in the accumulator, it was reading 10.1mpa. Tried to put into H but got the blinking light again. What I did was just drove around for 20 miles,and now everything works like normal. Lo N hi all work like before.

 

[ehrgeiz]

Just checking in for a further update. Replaced 2x height sensors with the Aisin units from Rock Auto. Note they have little plastic tabs to prevent you from over extending the sensor. Once you have it mounted it easily pops off with a little pressure. Good idea, good feature.

Heights are now very much better and the LX feels much better too. Able to move through L N and H without delay or issue. Ran out of time tonight to measure heights and cross level if needed, but will do so soon.

See below results from Tech Stream. Just need to get the rear pressures down. Will report back again once I have the Slee Spacer installed.

 

[suprarx7nut]

Hello,

I was hoping some of the AHC pros could be help me diagnose an issue. I have a 2000 Lexus LX470 Canadian model. I have a Rhino Rack, Columbus Variant RTT and a Alucab Shadow Awning mounted as well as a sleeping platform in the back. Not really much extra weight, maybe 250 lbs.

The story goes... about 1 month ago I had some noise in the front suspension. I dropped it off with my mechanic (not Lexus) to check it out and isolate it. The mechanic advised it was my sway bar bushing. He replaced the bushings.

I took a trip from Alberta to BC about 3 weeks ago for holidays. Had a Jumping Jack trailer on the hitch (light), but the LX was loaded up pretty good with coolers and kids etc. No real issues to speak of though. I noticed the AHC in L a couple of times, but would readjust to N.

About a 2 weeks ago, I noticed another annoying squeak in the front suspension. I dropped it off with the mechanic again who isolated it to the front right shock bushing. The penetrating oil made the noise go away so I figured I would leave it for now and see if it came back before replacing the bushing.

When I went to pick up the vehicle I hopped into the truck fired it up and noticed that the AHC was Off on the dash. I then noticed that the front was raked up high and the rear was low. Upon driving it was incredibly bouncy. Would not go into L or H. I limped it home and called the mechanic the next day inquiring as to if he maybe knocked the height sensor or used the AHC while the vehicle was suspended. He says nay.

I decided to bleed the system out and replace the AHC fluid. The fluid was very dark and I definitely saw some air bubbles. So much so I wasn't content with the single flush and did a second one earlier this week. On the second flush the fluid looked clean (pink-ish) with few air bubbles. I also popped off the right height sensor to see if I could examine any damage, or corrosion looked clean and perfect inside. I put it back on.

The system re-pressurized, but was still high in the front and a little bit bouncy, but not as bad. All my reading on similar issue threads lead me to believe that I needed a Tech Stream to figure WTF was up. Ordered up the cable and booted up the tech stream.

Here is the first data (remember I couldn't get from N to L). Pretty big delta on the FRH and FLH sensors. No trouble codes at all.

View attachment 3072802


For giggles I moved the FRH sensor to the highest point in the bracket (did not change the adjuster but though). Here is the result on the TS.

View attachment 3072803


Okay I pushed the AHC into low and drove a bit very slowly around the neighbourhood and it dropped into L. I connected the TS, then pushed N. Nothing happened, just a blinking light. Went for a drive and the system pushed into N. See below for the result in TS data. The MPA is really, really high. PS I pulled the temp sensor as recommended for pressure checks which produced the error code. Data for this posted in the below reply.


So, I'm inclined to start ratching up the torsion bars to try to reduce the MPA in the front system, but the rear is high too. I'm not really sure what to make of all this. I don't have super heavy bumpers or anything like that. With the pressures being so high is it fair to say that the pump and globes are good? I wonder if the height sensors are pooched and that's throwing everything out of order. Maybe my mechanic unknowingly reset the torsion bars when changing the sway bar bushing? Not really sure what to make of it all. Any thoughts or insight are very welcome!

Thanks in advance,

Dave

The pressure reading you see in Techstream has nothing to do with globe pressure. Totally separate pressure chambers. There's no way to measure the globes with Techstream. All you can do is the gradation test.

Roger!

Okay, 11x turns clockwise on the torsion bars and MPA is high 7's on front and back with me in the drivers seat. Not sure how many more tuns the torsion bar will go, getting pretty stiff!

Also, got the height sensors closer together, but not enough thread or brackets to bridge the gap. Still a sizable delta, but the system is working, goes up, goes down on command. The height sensors definitely seem shot. I'm going to order new FR and FL sensors. I see Amazon has a brand for cheap "A-Premium". AISIN has some on Rock Auto for a lot more coin. As I understand it these sensors are very simple, I'm thinking go cheap for such a basic sensor arm.

Also, have about 9 graduations between H and L. So guess the globes are still passable for now. Date on them bulb is 2000 so factory original. 22+ years service is pretty decent.

Ordered a Slee 30mm spacer for the rear springs too. When I've got the cooler, gear and trailer on hitch I figure I'm pushing the rear pressures so might be wise to reduce them a touch with spacer.

I must say that Tech Stream is the tits. Sure makes this all a lot easier!

Will report back with outcome for anyone else reading/ diagnosing AHC issues.

The aftermarket sensors are notorious for failing and I think that includes the Aisin from Rock Auto. If you hit some weird values and end up chasing your tail, you may want to source some genuine Toyota/Lexus sensors. It seems simple, but everyone except Toyota/Lexus seems to make garbage when it comes to AHC sensors.

 

[ehrgeiz]

The pressure reading you see in Techstream has nothing to do with globe pressure. Totally separate pressure chambers. There's no way to measure the globes with Techstream. All you can do is the gradation test.


The aftermarket sensors are notorious for failing and I think that includes the Aisin from Rock Auto. If you hit some weird values and end up chasing your tail, you may want to source some genuine Toyota/Lexus sensors. It seems simple, but everyone except Toyota/Lexus seems to make garbage when it comes to AHC sensors.

Hey, thanks for the additional input. Let's hope those Aisin's hold up! So far so good, but if something goes squirrely in time I'll report back for the benefit of the forum.

PS. still loving my SS1 sleeper from you. It's a very nice unit!

 

[suprarx7nut]

PS. still loving my SS1 sleeper from you. It's a very nice unit!

Awesome, great to hear!

 

[beachbumin]

Pretty sure I've gotten myself into fail safe mode. Replaced my globes and now I am stuck in low with the off light blinking. Assuming air in the lines caused the fail safe mode to engage.

I've ran techstream and pulled c1762. Everytime I try to clear it, the motor clicks, then the code comes back on. Active tests gave me the same results.

Should I keep trying to bleed the lines at each globe and hope that clears the air out or is there another step that I should take?

 

[suprarx7nut]

Pretty sure I've gotten myself into fail safe mode. Replaced my globes and now I am stuck in low with the off light blinking. Assuming air in the lines caused the fail safe mode to engage.

I've ran techstream and pulled c1762. Everytime I try to clear it, the motor clicks, then the code comes back on. Active tests gave me the same results.

Should I keep trying to bleed the lines at each globe and hope that clears the air out or is there another step that I should take?

View attachment 3082829

View attachment 3082830

That code gets set after a very small time period. I think 0.2 seconds. What you're describing sounds exactly like air in the lines and/or the dreaded gel stuck in the pump strainers.

If you can get any air bubbles out of any of the lines when bleeding, keep bleeding until you have perfect pure fluid out of each bleeder. Quite a tedious task unless you can get active test to cooperate and force the pump to run or hotwire the pump.

 

[beachbumin]

That code gets set after a very small time period. I think 0.2 seconds. What you're describing sounds exactly like air in the lines and/or the dreaded gel stuck in the pump strainers.

If you can get any air bubbles out of any of the lines when bleeding, keep bleeding until you have perfect pure fluid out of each bleeder. Quite a tedious task unless you can get active test to cooperate and force the pump to run

Update. After trying the run active tests to no avail I ended up direct wiring the pump motor and bleeding the lines. Eventually I was able to at least get the lx into N.

I removed the pump switch and took some wire and connected to the battery. I also cut a small piece of cardboard and slid it in between the 2 male posts exposed when the connector was released to be safe. As per posts here, I ran the ahc motor for 10 seconds then started bleeding. It took 3-4 times to clear the lines and get pressure to build up.

Hope that helps the next person to get stuck in fail safe mode!

 

[suprarx7nut]

Update. After trying the run active tests to no avail I ended up direct wiring the pump motor and bleeding the lines. Eventually I was able to at least get the lx into N.

I removed the pump switch and took some wire and connected to the battery. I also cut a small piece of cardboard and slid it in between the 2 male posts exposed when the connector was released to be safe. As per posts here, I ran the ahc motor for 10 seconds then started bleeding. It took 3-4 times to clear the lines and get pressure to build up.

Hope that helps the next person to get stuck in fail safe mode!

Nice work!

Active test seems to not work for many people, myself included a few times.

That oil pressure fail safe is a bit overly safe, it seems. I would like to see it run a little longer before stopping.

 

[willyroo]

Hi team - rather than start a new thread I thought I would post here. New to me LX470 with 194ks (approx 125k miles).

Following excellent suggestions from IndroCruise (who likely lives just over the other side of the Brisbane river from me ), I've got 4 new spheres on their way from Japan, and 2.5 litres of AHC fluid from my local Toyota dealer.

The AHC works N -> H and N-> L once the car has been for a drive. However if I start the car from cold, the H or L lights just flash and nothing happens if I try to raise or lower.

Techstream (on a Dell Latitude 7290 with W11 so a win err bad pun there) shows these values - you can see pressure sensor is 0.0.

Doing active test the car will go down (?) if I test certain solenoids.

Suggestions on what to do next appreciated - or do I just go and buy the 36mm fan clutch spanner and change globes (when they arrive) and AHC fluid, then report back?

 

[beachbumin]

You may want some more ahc fluid just to be safe. My neglected system took 1.5 metal jugs worth until it looks clean enough.