AHC (1 Viewer)

Joined
Feb 11, 2021
Messages
10
Location
Kenya
Hi guys, I just got an LX470. the previous owner had removed the original height control shocks and installed stiff gas shocks. Everything else related to this system is intact so i bought a set of OEM shocks and have installed them. The problem is now the pump cuts off when i try to raise the car and the error code shows insufficient pressure on the pressure sensor. What am i missing??
 
Joined
Dec 6, 2016
Messages
310
Location
Brisbane, Australia
Hi guys, I just got an LX470. the previous owner had removed the original height control shocks and installed stiff gas shocks. Everything else related to this system is intact so i bought a set of OEM shocks and have installed them. The problem is now the pump cuts off when i try to raise the car and the error code shows insufficient pressure on the pressure sensor. What am i missing??
Hi HarperKE,

The starting point is to give yourself (and your IH8MUD advisors) much more information. Ideally this would include at least a Techstream screenshot (the whole page including headings and buttons, not just an edited segment as sometimes appears on this Forum).

Meanwhile, here are some thought-starters …..

If you have not got Techstream or need help in setting it up the following thread provides excellent guidance:
How-To: TechStream In 5 Minutes - https://forum.ih8mud.com/threads/how-to-techstream-in-5-minutes.1034923/

The point is that the without Techstream or some other scanner which can read the AHC Electronic Control Unit and help with diagnosis, your efforts will be an exercise in frustration.

Suggest have a look at the diagrams and General Description in the document at the next link below and use the official Toyota/Lexus names for AHC parts so that all can know exactly what is being described and can help with diagnosis rather than guessing games. It is allowable to use the word ‘globe’ as shorthand for 'Gas Chamber':

https://lc100e.github.io/manual/
Look for the index tabs starting at top left hand side of the opening page and choose these tabs in order to reach the General Description document:
New Car Features > CHASSIS > Suspension > Active Height Control Suspension.

(This is a LC100 manual but the AHC details are exactly the same for LX470. By the way, the information from @Surfy is helpful but bear in mind that the AHC system on his LX570 is very different to the AHC system on your LX470).

In addition ….
  • What age is your vehicle?
  • How many kilometres?
  • When was AHC system deleted? (If long ago, then be suspicious of old remnant fluid which may have turned to jelly in the system you are now trying to re-instate – including in the tiny strainers within the AHC Pump),
  • When you say you used the “original fluid”, did you mean that you used new genuine Toyota/Lexus AHC Fluid Part No. 08886-01805 for 2.5 litre drum or Part No. 08886-81221 for 1 litre bottle? (It is not a good idea to re-use old AHC fluid -- it deteriorates with age and especially heat and loses some of its properties. It may contained dissolved air),
  • Do you have any reason to suspect that wrong fluid (such as brake fluid, steeing fluid or transmission fluid) has ever been used in the system? (Wrong fluid leads to degradation of soft components and results in blockages including at the AHC Pump),
  • What replacement front torsion bars and rear springs were used to replace the OEM units? (The OEM torsion bars and springs used on AHC vehicles are insufficient to carry the vehicle without an operational AHC system – take pictures if details are unknown),
  • What are the hub-to-fender heights on all corners, as measured with a tape-measure? (It is important to know heights at which the vehicle is sitting),
  • If you already have Techstream or similar, exactly which Diagnostic Trouble Codes (DTC’s) by number and name are showing on the trouble code readout?
Seems like a lot of questions but please bear in mind that you can see the vehicle and your IH8MUD advisors know only what you choose tell them or show them.

Also, please provide some pictures of the suspension parts so that your IH8MUD advisors can see what you can see.

Even though the Pressure Sensor is new, it only takes a few minutes to test it:

https://lc100e.github.io/manual/ ,
then follow these tabs in the index panel on the Left Hand Side of the opening page:
Repair Manual > DIAGNOSTICS > ACTIVE HEIGHT CONTROL SUSPENSION & SKYHOOK ITEMS > C1718/18 – FLUID PRESSURE SENSOR CIRCUIT > Page 3

It is worthwhile to read the entire AHC Diagnostics section at the above link. It is quite possible that the AHC ECU has directed the AHC/TEMS system into one of several ‘fail safe modes’ which are described in this section of the Factory Service Manual. The description of the various symptoms accompanying each ‘fail safe mode’ are helpful.

You mention that “the problem with directly running the pump is the solenoid block under the chassis won't open to let fluid flow”. What does this mean? Have you been able to confirm positively that there are problems within the Control Valve Assembly (on the LHS chassis rail on the inner side)? Or are you referring to problems with the solenoid valve at the front end of the Height Control Accumulator (on the LHS chassis rail on the outer side)?

Meanwhile, you may wish to try the “Active Test” – see Page 3 of the first attachment. This provides a way of getting the AHC Pump to start.

If you have not seen them, also suggest having a look at the “Cheat Sheet”, video and explanation at this link:
Builds - The YotaMD Build - Cypress - https://forum.ih8mud.com/threads/the-yotamd-build-cypress.1184210/page-9#post-13383404

And also the “ABC’s of AHC” at this link:
The ABCs of AHC - How to Measure, Flush, and Adjust all in one place - https://forum.ih8mud.com/threads/the-abcs-of-ahc-how-to-measure-flush-and-adjust-all-in-one-place.1211999/#post-13116520

See Post #67 by @BullElk at AHC pump out? - https://forum.ih8mud.com/threads/ahc-pump-out.1226629/page-4#post-13401098 for pictures of a clogged pump.

See Posts #69 and #70 at AHC pump out? - https://forum.ih8mud.com/threads/ahc-pump-out.1226629/page-4#post-13407297 and onwards shows pictures of AHC Pump disassembly and also show the tiny filters (strainers) within the Pump. Pump disassembly. Cleanup of the pump and backwashing the filters (strainers) is straightforward and is made easy by removing the motor/pump/tank assembly from the vehicle.
 

Attachments

  • AHC suspension precheck and damper check.pdf
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  • AHC TSB for Diagnosis & Repair Procedure of AHC Pump Sub-Assembly_CP3006_1_1 (6).pdf
    387.3 KB · Views: 6
Joined
Apr 18, 2020
Messages
25
Location
Little Rock, Arkansas
Hey, just replaced the AHC "shocks" with new ones and had the same thing exact thing happen after. Here's what fixed it for me:

1) do the short out method of the diagnostic port in the hood
2) bleed all 5 positions of the AHC
- I got to the point that my accumulator had no pressure coming up, but the front globes still did. Bleeding this eventually resolved the problem such that the system was again able to get to high.
 

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