AHC does not exist but was never deleted?? Help?! (1 Viewer)

Joined
May 23, 2021
Messages
56
Location
Nigeria
Ok, first post on this site. I (my dad) have a first-hand, dealership-bought 2000 LX470 with 113k miles on it, everything is all well and good until we get to a speed bump in the road, if I drive over it going anything above 10 miles per hour, the car bounces HARD and you can hear the front tires scraping the top of the tire bay as the nose dives down off the bump. Anycrap, the AHC system is NOT WORKING. Like, it's non-existent, it's like someone did a really good electrical delete of the system but didn't change any of the actual hardware. We tried using the AHC switch (the one diagonally toward you from the gear selector if you're sitting in driver's seat) and there was no response, the light on the dash was not showing AT ALL (like nothing AHC related was showing on dash) but you could clearly see the provision in the dash for the AHC lights. So we went to the mechanic everyday for literally a week, there was no hydraulic in the front shocks (the hydraulic in the rear was still intact but we bled the system from the globes so that's gone too). We checked all the shocks, the one in the passenger side was leaking and replaced, we checked the AHC pump, it was working fine, of course it wasn't working when connected to the car, but we connected it directly to the battery and it ran, we checked the AHC ECU and it was working, we checked every single fuse in each fuse box, the one in the engine bay, the one at driver's side, and the one at passenger's side, and each fuse was working, and bad ones were replaced. We tried 2 other ECUs and still no response, we checked the AHC switch i talked about earlier, it was working fine, every single damn thing was working as it should. AND YET, when we connected an OOBD-II and ran diagnostics, the computer said there was no AHC present (well it said something along that line, this was back in December 2020) and the mechanic/electrician guy said that according to the code and what the computer said, the AHC system is not even connected to the ECU and it's like the AHC doesn't exist in the car. So my question is, how on God's earth can every single thing be intact and working as it should, and still, the AHC system is not working, the AHC dash light is not working, and the AHC is basically deleted??
 
Solution
I fixed it!!! :cheers::rofl: Turns out the 20A AHC-IG fuse in the driver's side fuse box wasn't there. Found a spare 20A in the engine bay fuse box and used that. Turned ignition on and the Dash lights for AHC came on. Jumped around in circles, went and called my brother to witness the greatness. Got in the car, closed all doors and started it. Car raised to N mode and is currently sitting there. My dad came downstairs and I showed him, we took a spin around the neighborhood, purposely going into bumps and pulling high speeds otherwise highly uncomfortable before and the suspension was working like butter, literally like runny buttery smooth. Car was handling perfectly and i've never loved it more than I do this morning. So yeah...
Joined
May 23, 2021
Messages
56
Location
Nigeria
I fixed it!!! :cheers::rofl: Turns out the 20A AHC-IG fuse in the driver's side fuse box wasn't there. Found a spare 20A in the engine bay fuse box and used that. Turned ignition on and the Dash lights for AHC came on. Jumped around in circles, went and called my brother to witness the greatness. Got in the car, closed all doors and started it. Car raised to N mode and is currently sitting there. My dad came downstairs and I showed him, we took a spin around the neighborhood, purposely going into bumps and pulling high speeds otherwise highly uncomfortable before and the suspension was working like butter, literally like runny buttery smooth. Car was handling perfectly and i've never loved it more than I do this morning. So yeah, Nigerian mechanics and electricians can bite me lol.

If you're wondering, I just reasoned it out. The AHC dash light has never been working, since I was a kid I can swear I never saw that light on the dash, it's as if the AHC was deleted, so if you deleted the AHC, what fuses would you have to pull to disable the dash lights? Went on this thread: AHC Removal - Fuses vs ECU - https://forum.ih8mud.com/threads/ahc-removal-fuses-vs-ecu.1134601/ and lo and behold the damn AHC-IG was pulled! Fit it in with a spare 20A and it was working EZ.

But now a new problem arises. The ride height is stuck in N mode (which is no problem as long as the car is stable when driving) and won't go up to HI and won't come down to LOW even when the car is parked, all doors locked, parking brake on, it still won't budge. What's the issue with that? The fluid level in the AHC reservoir is below min so will top up at later date, but I just wanna know what's causing the height not to change. Also when i press the OFF button, it doesn't indicate OFF on the dash. Maybe that AHC switch near the gear isn't connected properly? What else could it be? I'll take any info I can get because from the 3 years i've been working on my dad's cars i've come to see (and this case proves it beyond doubt) that there are many ways to tackle different issues in cars and even the most irrelevant information can get you thinking from a different angle. Cheers!!
 
Solution
Joined
Dec 6, 2016
Messages
393
Location
Brisbane, Australia
I fixed it!!! :cheers::rofl: Turns out the 20A AHC-IG fuse in the driver's side fuse box wasn't there. Found a spare 20A in the engine bay fuse box and used that. Turned ignition on and the Dash lights for AHC came on. Jumped around in circles, went and called my brother to witness the greatness. Got in the car, closed all doors and started it. Car raised to N mode and is currently sitting there. My dad came downstairs and I showed him, we took a spin around the neighborhood, purposely going into bumps and pulling high speeds otherwise highly uncomfortable before and the suspension was working like butter, literally like runny buttery smooth. Car was handling perfectly and i've never loved it more than I do this morning. So yeah, Nigerian mechanics and electricians can bite me lol.

If you're wondering, I just reasoned it out. The AHC dash light has never been working, since I was a kid I can swear I never saw that light on the dash, it's as if the AHC was deleted, so if you deleted the AHC, what fuses would you have to pull to disable the dash lights? Went on this thread: AHC Removal - Fuses vs ECU - https://forum.ih8mud.com/threads/ahc-removal-fuses-vs-ecu.1134601/ and lo and behold the damn AHC-IG was pulled! Fit it in with a spare 20A and it was working EZ.

But now a new problem arises. The ride height is stuck in N mode (which is no problem as long as the car is stable when driving) and won't go up to HI and won't come down to LOW even when the car is parked, all doors locked, parking brake on, it still won't budge. What's the issue with that? The fluid level in the AHC reservoir is below min so will top up at later date, but I just wanna know what's causing the height not to change. Also when i press the OFF button, it doesn't indicate OFF on the dash. Maybe that AHC switch near the gear isn't connected properly? What else could it be? I'll take any info I can get because from the 3 years i've been working on my dad's cars i've come to see (and this case proves it beyond doubt) that there are many ways to tackle different issues in cars and even the most irrelevant information can get you thinking from a different angle. Cheers!!

For the inquiring mind – if not seen previously ….

https://lc100e.github.io/manual/ (genuine Toyota LC100 Factory Service Manual including AHC – also relevant to LX470)
Then follow the index tabs, starting at the top left of the opening page:
New Car Features > CHASSIS > Suspension > Active Height Control & Skyhook TEMS
This opens to a 20 page general description and diagrams of the Active Height Control (AHC) system and the Toyota Electronic Modulated Suspension (TEMS) system and how these systems operate.

https://lc100e.github.io/manual/, then follow these tabs:
Repair Manual > DIAGNOSTICS > ACTIVE HEIGHT CONTROL SUSPENSION & SKYHOOK TEMS
This long section provides a diagnostic process as well as many insights if read closely.
Suggest read the “Problem Symptoms Table”, also read through all of the fault code listings, looking particularly at the various ‘fail safe modes’ as it seems possible that these may be relevant, given the description in your post. You may find something that is a reasonable match to the symptoms observed – and/or that may suggest some starting points.

https://lc100e.github.io/manual/, then follow these tabs:
Repair Manual > SUSPENSION AND AXLE > ACTIVE HEIGHT CONTROL SYSTEM (Independent Front Suspension) > ON-VEHICLE INSPECTION
This section provides most AHC specification issues. It may give a few more ideas to test.

If not already done, suggest use Techstream for diagnosis rather than universal OBD2 scanners ....

 
Joined
May 23, 2021
Messages
56
Location
Nigeria
For the inquiring mind – if not seen previously ….

https://lc100e.github.io/manual/ (genuine Toyota LC100 Factory Service Manual including AHC – also relevant to LX470)
Then follow the index tabs, starting at the top left of the opening page:
New Car Features > CHASSIS > Suspension > Active Height Control & Skyhook TEMS
This opens to a 20 page general description and diagrams of the Active Height Control (AHC) system and the Toyota Electronic Modulated Suspension (TEMS) system and how these systems operate.

https://lc100e.github.io/manual/, then follow these tabs:
Repair Manual > DIAGNOSTICS > ACTIVE HEIGHT CONTROL SUSPENSION & SKYHOOK TEMS
This long section provides a diagnostic process as well as many insights if read closely.
Suggest read the “Problem Symptoms Table”, also read through all of the fault code listings, looking particularly at the various ‘fail safe modes’ as it seems possible that these may be relevant, given the description in your post. You may find something that is a reasonable match to the symptoms observed – and/or that may suggest some starting points.

https://lc100e.github.io/manual/, then follow these tabs:
Repair Manual > SUSPENSION AND AXLE > ACTIVE HEIGHT CONTROL SYSTEM (Independent Front Suspension) > ON-VEHICLE INSPECTION
This section provides most AHC specification issues. It may give a few more ideas to test.

If not already done, suggest use Techstream for diagnosis rather than universal OBD2 scanners ....

Thanks for the service manual, really really really needed that right now, sadly, the links ( this one: https://lc100e.github.io/manual/) are well nevermind that lol, connected to a VPN and it's working EZ. Big Cheers!!!
 

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