LX470, AHC lifts up in the front when coming to a complete stop. (1 Viewer)

[ytrakas]

Hey, I've noticed my car lifts up in the front when I come to a complete stop. Why does the car do this? I would assume the car is more aerodynamic with rake right?

 

[TexLexican]

Hey, I've noticed my car lifts up in the front when I come to a complete stop. Why does the car do this? I would assume the car is more aerodynamic with rake right?

Maybe the momentum of the car tricks the sensors into adjusting due to the weight being distributed to the front.

 

[GTV]

It's normal.

 

[ytrakas]

It's normal.

Yes I know, just wondering why the car does that

 

[IndroCruise]

Yes I know, just wondering why the car does that

When making a stop, the front may sink some, even though the anti-dive feature of AHC and TEMS systems reduce (but do not eliminate) the dive effect.

This might just be due to the 'springiness' of the nitrogen gas in healthy 'globes' -- compression and decompression of the nitrogen while the vehicle is travelling is the 'gas spring' function of the 'globes'.

If the Front has sunk and AHC Fluid has been displaced to the AHC Tank, then the change in vehicle posture will be noticed by the two Front Height Control Sensors. These send small voltage signals to the Suspension Electronic Control Unit (ECU). The voltages are proportional to the height of the vehicle. If these signals indicate that the Front height is low, then the ECU responds by causing the AHC Pump to run briefly, sending pressure and volume of AHC Fluid to the Front 'shock absorbers'. On an AHC-equipped vehicle, the so-called 'shock absorbers' really are just hydraulic struts -- very different to conventional shock absorbers. The increased fluid pressure and volume arriving at the Front AHC 'shock absorbers' cause the Front of the vehicle to raise until the ECU receives the correct voltage signal from the Height Control Sensors for "N" height (or "LO" height or "HI" height, whatever has been selected at the switch on the centre console).

This is just part of the AHC system doing its as-designed automatic self-adjusting height thing -- which is the reason it is called Active Height Control. It works provided the overall vehicle weight is within limits and provided the system is healthy and correctly adjusted -- particularly the Height Control Sensors (two at the Front, one at the Rear) and provided that the AHC Pump is working properly.

Read all about this in the illustrated General Description of the Active Height Control (AHC) system and the Toyota Electronic Modulated Suspension (TEMS) system at the link below. This link leads to the relevant section of the on-line LC100 Factory Service Manual as produced by Toyota. The AHC and TEMS systems on LX470 are the same under the skin as for LC100:

LC100 Workshop Manual - https://lc100e.github.io/
then follow these tabs in the index panel at the LHS of the opening page:
+ New Car Features
+ CHASSIS
+ Suspension
+ Active Height Control Suspension and Skyhook TEMS

The document at this final tab is about 20 pages long -- it is a good general read with good diagrams.

 

[suprarx7nut]

Hey, I've noticed my car lifts up in the front when I come to a complete stop. Why does the car do this? I would assume the car is more aerodynamic with rake right?

Normal and expected behavior. It adjusts while you drive as well, but you can't notice it as easily as that post-stop adjustment.