AHC bleeding questions - I'm worried

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90WT

90WT

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Bozeman, MT
Looking for some help as I prep for Cruise Moab. I'm starting to worry.

Question on how best to bleed and what to expect.

I replaced the front shock bushings last week, which required disconnecting the front AHC lines to the top of the shock. I bled the accumulator and front globes (it was in L at the time) When I first turned on the rig, I cycled it up and down a bunch of times. It seemed to be working fine, but I noticed a significant lean. Passenger side down at least an inch lower than drivers side. I'm guessing I most likely did not bleed enough and drew air deeper into the system. I have tried to manually bleed all the globes (4-5 times each) and accumulator (2 ties) and still have slow or no raising from N to H. Immediately after bleeding, it takes a lot of pump cycles to get just get from L to N.

I am using Techstream to clear the C1751 and C1762 codes in order to cycle the pump after I manually bleed a globe corner. It takes a lot of cycles to get some pressure in the system. During which my pump makes a higher pitch whine. Until the vehicle starts to raise, at which the pump is more quiet and sounds normal.

Questions:
How many pump cycles are necessary to build pressure in the system after I manually bleed a one globe?
Does the accumulator need to be bled at the same time as the globes?
Should I be bleeding rear globe, accumulator, and front globe all at the same drain? All the way to bumpstops or 6oz at a time? And then have the system cycle to gain pressure?
In Techstream, the utility function to bleed the system doesn't seem to be an option or at least I can't figure out that method and I haven't jumped the connector in the engine bay. Do I need to run this utility in order for a successful bleed? Or can I keep doing what I'm doing? I don't want to burn up something in the process.

I have been reading this thread:
AHC Inop after fluid change 2007 lx C1751 and C1762

2006 LX470, 205k miles
AHC has always worked. Fluid change a month ago before I found out the shock bushings were bad.
Front end alignment before I started the work so TBs were correctly adjusted.
New shock bushings on the front.

I hope I'm on the right track and not overlooking something that needs replaced. I'm losing my window of time to order new parts and install before Cruise Moab if necessary.
Thanks.
 
Answered one of my own questions: the utility bleed is king. I jumped the Ts & E1 on the DLC1 box. Pushed the AHC button down 5 times, turned to comfort mode, pushed the AHC button up and the pump cycled for 10 seconds or so. I repeated this utility bleed 5 times to get enough pressure and height to be equal to N mode (my rig was stuck in L mode or even lower). During one final utility bleed, after it runs for the 10 seconds, I found out you can push and hold up on the AHC button and it continued to add pressure/height. Be careful, there is no height restriction, you could possibly raise to a damage level. This was only raising the front of my rig. I'm not sure why.
Turned car off. Turned key to On position to put the AHC in N mode, as it still showed L mode even when raised so high. Turned on engine, car lowered front to N height and raised rear to N height. Cycled the AHC height from N to H a couple of times. It appears to be working. I'm gonna have lunch then work up the courage to drop to L and raise from there without the utility bleed.
 
I'm seeing positive results, but after many iterations of manual bleed one globe, use utility bleed function to raise pressures (and vehicle height back to N), then cycle N to H a few times. Then back to N. Then start over.

I am still getting some air from the globes. But nothing is frothy or looking like a guiness head. Bubbles look like ones from a brake bleed.
Front and rear globes are not connected, so I'm bleeding on the front globes, 6 oz or so at a time, one side at a time.
The rig really wants to be level, to do the utility bleed. It doesn't like my slightly sloped driveway. I had to move to the level street.
I'm not bleeding the accumulator.
Running the utility bleed, jump the connector in the engine bay, and techstream is hooked up from the OBDII port in the footwell at the same time and reading ok.
High pitch wine from the AHC pump means its not pumping. You should hear a nice medium/low pitch hum from the pump when its pushing fluid.
 
Were the globes replaced or are they still original?

I bled and bled my globes and air just kept coming out. Ended up reading a post on this forum that recommended letting the truck sit parked in L for 30 minutes, then raise it up to H for 30 minutes, and then back to L for 30 minutes, back to H, etc through the course of a day and that helped get the air out of my system better than anything.

The reasoning is that inside the hydraulic lines the pressure is very high which allows air to dissolve into the fluid. By cycling the height, it exchanges the high pressure fluid with the fluid sitting in the reservoir at atmospheric pressure and allows the air to leave the fluid easier.

The AHC system is self bleeding from what I understand, it just takes time and cycling the suspension.
 
Still original globes. I had good gradations when I flushed the system a month ago, although I can't recall the exact number.
I like your approach. Right now, I can't always go from L to N.
I'll take your advice and see if the 30 minute intervals throughout today get the last bit of air out.
 
Last edited:
Tbars are original. When I was able to cycle from L to N yesterday, pressures on the front were 6.7 ish.
King Springs in the back. Rear pressures were 4.5 ish.
 
J1000 said:
I bled and bled my globes and air just kept coming out. Ended up reading a post on this forum that recommended letting the truck sit parked in L for 30 minutes, then raise it up to H for 30 minutes, and then back to L for 30 minutes, back to H, etc through the course of a day and that helped get the air out of my system better than anything.

The reasoning is that inside the hydraulic lines the pressure is very high which allows air to dissolve into the fluid. By cycling the height, it exchanges the high pressure fluid with the fluid sitting in the reservoir at atmospheric pressure and allows the air to leave the fluid easier.

The AHC system is self bleeding from what I understand, it just takes time and cycling the suspension.
Click to expand...
This seems to have done the trick. Thanks for the tip!
 
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