I replaced my rear springs (2006 with 238k) and added 30mm spacers and it got me a whopping 0.2-0.3ish MPa rear pressure gains... I was a little disappointed.
Current specs after crossleveling and torsion bar pressure adjustment:
FR Height Control Sensor: -0.3 inch
FL Height Control Sensor: 0.0 inch
RR Height Control Sensor: -0.2 inch
Front Pressure Sensor: 6.7 MPa
Rear Pressure Sensor: 6.6 MPa
Accumulator Press Sensor: 10.6 MPa
Do I mess with the FR height sensor and RR height sensor to get closer to 0.0 or just let it ride? It's ever so slightly low on the hub-to-fender measurement.
If new OEM AHC springs, then AHC pressures are function of the weight of the vehicle and the 'ride height' of the vehicle at the "N" height setting -- more weight than stock and/or more height than stock means more AHC pressure. If Rear AHC pressure is not sufficiently corrected by a spacers (which causes pre-loading of the springs), then more spring rate is necessary, such as with King KTRS-79 springs.
You already understand the Height Control Sensor readings -- but to set it out again for anybody else who comes this way ....
Suggest re-check front cross-level on level ground -- “level” means a levelled concrete surface like a garage, or within a built parking station, or similar -- not in the street nor in an open parking lot -- these are cambered or sloped to drain and are neither flat nor level by design (or lack of design). Then look for tape-measurements hub-to-fender which are equal within FSM-specified tolerance of +/- 10 mm (0.39 inches), adjusting the equalisation if necessary using ONLY the torsion bar adjusters with engine OFF per FSM, and NOT using the Height Control Sensor adjusters. At this point, the actual hub-to-fender measurements are interesting but unimportant -- it is the
equal heights within tolerance which are important. Vehicle ‘ride height adjustment’ is a separate step which comes later -- on an AHC-equipped vehicle ‘ride height adjustment’ is NOT done using the torsion bar adjusters.
A check of Front cross-levelling is the starting point for any adjustments on the AHC system.
By the way, the hub-to-fender measurements are not the FSM-specified method of vehicle height measurement but are an easy-to-use, widely recognised and reliable approximation. The FSM method is more accurate but is very fiddly and inconvenient.
With the Front of the vehicle properly cross-levelled, and with vehicle in “N” height setting and still on level ground, check Height Control Sensor readings Front Left, Front Right and the single Rear sensor on Techstream (or other suitable reader), looking for zero within FSM-specified tolerance of +/- 5 mm (0.2 inches).
If necessary, adjust the Sensors with engine OFF by using the slider adjustment to obtain as close to zero as possible -- can use the threaded heim arrangement on the Front sensors (not fitted on the Rear sensor) but these are very fiddly so suggest use slider first (as also mentioned in FSM).
Suggest be wary of “pursuit of perfection” in these measurements and adjustments. There can be some variation, especially if the ground is not level, or due to age and wear of suspension components and bushings, and/or small variations in manufacture of the vehicle (although Toyota/Lexus manufacturing tolerances are quite tight), and/or body or chassis damage in an accident or very hard use, etc, etc -- which can cause the vehicle to settle a little differently from time to time -- this is the purpose of the “tolerances”.
Suggest be aware that Height Control Sensors cannot be used to adjust side-to-side vehicle height differences on the AHC/TEMS system on LX470 (or LC100 where fitted). Attempting to do so is guaranteed to lead to frustration and re-work.
This is because the Gate Valves in the Control Valve Assembly are “normally open” when the vehicle is stationary or not cornering at speed. This means the pipework connecting the Front Right and Front Left sides of the suspension equalise the system pressures on Front Right and Front Left sides (ditto at the Rear) when the vehicle is stationary or not cornering at speed.
If the Height Control Sensor readings are different, then then the ECU works out an average and commands an up/down signal to get the sum displacement to zero -- if one sensor says +2 and the other says -2 then the sum displacement is 0 -- the ECU causes the vehicle adopt a vehicle height related to the average of the readings.
If the differences in Height Control Sensor readings readings are too far different, then the ECU may be unable to resolve the differences and may put the vehicle in ‘fail safe mode’ – fixed height, fixed damping, no automatic AHC or TEMS response, rough ride. Sometimes this is indicative of a failed sensor -- especially if the fixed height is strangely high or low.
‘Ride height adjustment’ is achieved by setting the vehicle at the desired height at “N” height setting (using jacks or some form of lift or by using the “Active Test” procedure), then adjusting the Height Control Sensors as close as possible to zero with the engine OFF. The vehicle is then set to return to this height at “N” height setting, provided the system is healthy and not overloaded. The ECU determines the heights at “LO” and “HI” height settings -- these cannot be adjusted independently of the “N” height setting.
slight improvement for a while
