Low AHC Fluid Question (1 Viewer)

Joined
Aug 8, 2020
Messages
44
Location
alabama
Of course the day after I post in here bragging about my new rig I find a potential problem. Looking for some advice.

So I was checking my fluids and I thought everything was fine, but when backlighting the reservoir, I noticed the AHC fluid is very low.

I’ve tested it before and the AHC still works with vehicle going to H and L. Ride doesn’t seem overly bumpy or anything. Maybe a bit bouncy, but nothing crazy.

Anyway just wanted thoughts on what I should do here. Can I just get some fluid and add it? Should I do a flush? Any advice is appreciated.
 
Joined
Aug 8, 2020
Messages
44
Location
alabama
Definitely not nice and pink. Darker for sure.

Fluid is 4, almost 5 ticks from the bottom of the reservoir.
 

ramangain

Clarksonian disciple
SILVER Star
Joined
Feb 6, 2020
Messages
2,506
Location
Atlantis
I set my fluid level at the MAX line when in N, and add a bit more for good measure.
 
Joined
Dec 6, 2016
Messages
310
Location
Brisbane, Australia
Ha. Yea guess I deserve that.

Ive taken a look underneath and don’t see any signs of a leak anywhere.

Standard recommendation is to bleed and completely flush AHC fluid where its age is unknown. There are many reports on IH8MUD that a fluid change improves ride quality, perhaps due to degraded characteristics of old fluid. Probably you already know that it is important to use only genuine Toyota/Lexus AHC Fluid (Part No. 08886-01805 in 2.5 litre drum or Part No. 08886-81221 in 1 litre plastic bottle) in the AHC system. Other fluids can cause major problems and damage to internal parts of the AHC system. There are many good posts on IH8MUD on how to bleed/flush AHC fluid – this requires care but it is not difficult. Search for the @PADDO method, also suggest take look at


and the AHC video and 'cheat sheet' at


It is important to be quite sure that the current fluid level is not so low as to allow air to enter the pump – for example when raising to “HI” setting and/or on a steep grade etc. If concerned just add fluid to bring the level at least up to the max/min marks until you can do a complete bleed/flush.

Serious leaks will be obvious from underbody inspection.

New fluid appears as below at "N" height – admittedly with the advantage of a new AHC tank! (RHD vehicle shown, LHD vehicles have the pump facing the firewall).

AHC Tank.jpg
 
Last edited:
Joined
Aug 8, 2020
Messages
44
Location
alabama
Thank you @IndroCruise. This is really good info.

Honestly that is the route I figured I should take, but I’ve heard/read that if the AHC fluid is really low, you may should hold off on a flush.

But I think what you recommended is what I will do. Add some fluid to make sure it has enough and no air will enter, then do the bleed and flush.

Thanks again for all of the info, guys.
 
Last edited:
Joined
Aug 8, 2020
Messages
44
Location
alabama
Quick question on this.

i have fluid ordered and will be attempting as soon as it comes in.

Do I need to take off running boards in order to do the bleed/flush? I’ve read about car dropping lower than LOW when bleeding and it seems it may be even more difficult with running boards on. Just want to be safe while doing this.

Also no need for sarcasm about running boards. Short wife and little kids require me to keep them. 😉
 

ramangain

Clarksonian disciple
SILVER Star
Joined
Feb 6, 2020
Messages
2,506
Location
Atlantis
I'm fat and I manage with running boards installed. You just need to get your head under there to see, not your body.
 
Joined
Aug 8, 2020
Messages
44
Location
alabama
Haha I gotcha. Thanks for replying and the brutal honesty.

I’m actually a smaller guy, but I’ve got a pretty big head......
 

uHu

Bridgeburner
Joined
Nov 27, 2005
Messages
2,074
Location
Oslo, Norway
Low ahc fluid can mean that the globes are low, that they have lost some nitrogen pressure. If you check pressures and heights, and then the globes test with measuring fluid level from Lo to Hi, you'll find an indication on the state of your globes.
 
Joined
Dec 6, 2016
Messages
310
Location
Brisbane, Australia
Quick question on this.

i have fluid ordered and will be attempting as soon as it comes in.

Do I need to take off running boards in order to do the bleed/flush? I’ve read about car dropping lower than LOW when bleeding and it seems it may be even more difficult with running boards on. Just want to be safe while doing this.

Also no need for sarcasm about running boards. Short wife and little kids require me to keep them. 😉

@uHu offers a good reminder.

These are the possibilities for “Low AHC Fluid”:
  1. the AHC Tank was not topped up to correct level at the time of a bleed/flush by a previous Owner – record of previous fluid change not known in this case (?), or,
  2. there is a significant leak – no leaks reported in this case, or,
  3. there has been some change in the life of the vehicle which has caused high AHC pressures to overwhelm the nitrogen pressure on the gas side of the membrane (diaphragm) and the membrane is less able to push fluid back to the tank – can happen when heavy fittings and accessories are added without torsion bar adjustment and attention to rear springs to correct AHC pressures, not reported in this case, or,
  4. as the ‘globes’ slowly (and naturally) deteriorate over the years, more and more fluid resides in the ‘globes’ as the weakening nitrogen pressure allows the membrane to be pushed further towards the back of the ‘globe’ and eventually the 'globe' may fill with AHC fluid – likely – happens to us all eventually!
A declining change in graduations at the AHC tank when moving from “LO” height to “HI” height indicates what is happening in Case (4) above:
  • around 14 graduations: similar to new ‘globes’;
  • around 9 graduations: slight decline in ride quality is starting to be noticed and "comfort" switch is less effective than before;
  • 7 graduations: time to replace ‘globes’, too much nitrogen pressure has been lost,

Be wary of a ‘false reading’ which can be obtained in Case (3) above, so first ensure AHC pressures are in the FSM-specified range and heights or at least be aware of this effect.

Practical Notes:
  • Before bleeding, give bleeder nipples/plugs a good dose of penetrating oil, eg PB Blaster or similar, the day before the work, especially if corrosion is present,
  • Consider pre-purchase of new bleeder nipples/plugs (49189-60010) and caps (49177-60010) to replace old – five required, not expensive,
  • Lie alongside vehicle, no person parts under vehicle,
  • AHC pressures are substantial, just crack open bleeders to start,
  • To avoid unnecessary mess, be ready to close bleeder screw quickly if hose flies off bleeder due to pressure,
  • Wear eye protection just in case,
  • Be ready for vehicle to drop to bump stops – care required but not necessary to remove running boards – and as an old short round person with grandchildren I see no shame in keeping running boards!
For more general information about how the AHC/TEMS system works, see Factory Service Manual at:
https://lc100e.github.io/manual/
(Follow the index tabs starting at the top: New Car Features > CHASSIS > Suspension > Active Height Control Suspension)

In this and other posts and attachments: "Gas Chambers" = "Globes" = "Spheres"


AHC Globe Pictorial.JPG
 

Attachments

  • AHC HI-LO Test per FSM.pdf
    105.1 KB · Views: 15
Joined
Aug 8, 2020
Messages
44
Location
alabama
Wow. This is really excellent info. Thanks all for this. Special shout out to @IndroCruise. I really appreciate the detailed write ups.

I will keep all posted on how everything turns out.
 

Lonegrasshopper

SILVER Star
Joined
Sep 18, 2014
Messages
237
Location
Dallas, TX
Wow. This is really excellent info. Thanks all for this. Special shout out to @IndroCruise. I really appreciate the detailed write ups.

I will keep all posted on how everything turns out.
Changing the fluid is stupid easy. It will take you about 45-60 minutes to complete, but most of that time will be setting up and crawling around. Easier than brake fluid change, basically the same concept, but minus some steps.
 

Users who are viewing this thread

Top Bottom