Late Edit: Pic of location of AHC IG fuse added.
One of my own basic mistakes is to forget to close all doors and the rear hatch on the vehicle when doing AHC tests. If any of these are open, the AHC system is prevented from operating for safety reasons. The system is interlocked with the door switches. It is OK if the engine hood is open – because there is no interlock switch here.
As already mentioned by
@suprarx7nut , it is important to start the investigation by clearing the Diagnostic Trouble Codes (DTC’s) which may have accumulated in the Electronic Control System (ECU) memory. If some DTC’s return after clearing, then that indicates real ongoing faults which will need to be resolved.
Suggest post these ongoing faults on this IH8MUD thread so that Members can offer further comments:
There are several ways to clear DTC’s:
Use the clearing function on the handheld device or Techstream.
If unsuccessful, use the manual method described at Post #6 at this link to clear DTC’s:
AHC wont raise after battery out - https://forum.ih8mud.com/threads/ahc-wont-raise-after-battery-out.1250534/#post-13814584
Alternatively, try re-booting the system. To do this, disconnect the battery or batteries and allow the system to power down, then re-connect the battery or batteries and re-start.
A fluid leak was mentioned. If the AHC Pump ran dry even if only momentarily, it will have stopped momentarily, at least until it was re-primed with AHC Fluid. In this case, these Diagnostic Trouble Codes (DTC) may be recorded by the ECU and will need to be cleared:
C1751 – AHC Pump & Motor
C1762 – Pressure Malfunction
It is also possible that an electrical disruption such as ‘jump starting’ may cause the AHC Main Relay to stop and show this DTC:
C1743 – AHC Main Relay Function
Some hints on overcoming this problem are found at Post #1 by
@PADDO at this link:
AHC DTC C1743 - main relay - https://forum.ih8mud.com/threads/ahc-dtc-c1743-main-relay.914138/
(Refers to AHC IG fuse which is found here -- behind cover in Left Hand footwell):
View attachment 2673836
Hopefully, you will not see the DTC which indicates malfunction of the ECU. If it appears, it indicates that the ECU has stopped due to internal memory errors. This requires replacement of the ECU. The AHC system will not work correctly and may not work at all with a faulty ECU.
C1761 – Malfunction of ECU
If you wish to explore the "Diagnostic Section" and "On-vehicle Section" of the Factory Service Manual (FSM) for Active Height Control (AHC) and the Toyota Electronic Modulated Suspension (TEMS), then the following are useful references:
AHC Diagnostics:
https://lc100e.github.io/manual/
At this link, use the Index on the left hand side of the opening page and follow these tabs:
Repair Manual > DIAGNOSTICS > ACTIVE HEIGHT CONTROL & SKYHOOK TEMS
AHC On-Vehicle Inspection including correct AHC pressure ranges:
https://lc100e.github.io/manual/
At this link, use the Index on the left hand side of the opening page and follow these tabs:
Repair Manual > SUSPENSION AND AXLE > ACTIVE HEIGHT CONTROL SYSTEM (Independent Front Suspension) > ON-VEHICLE INSPECTION
Hope this gives you a few thought-starters!
