Electronic Height Control?

[Chippy01]

My '07 T-Spirit went in for it's 70,000 mile service today.

When I went back to pick it up, I was informed of the following:-

Front discs starting show wear lines/ridges and lipping on thier edges (I knew this and was going to source new ones soon)

Front pads wearing close to the limit (This one would be linked to the disc wear and the wear lines)

Rear discs corroding badly (I've known this for a while and been putting replacement on the long finger)

Rear pads wearing unevenly (This again is linked to the bad discs)

So far, no real surprises.

Then I get told that the 'electronic height sensor' has failed due to corrosion (a link arm has snapped)

So, who can tell me what an electronic height sensor is? and what does it do? and how much do they cost?

The only height sensors that I know of are on Lexus LS430's, and they control the adjustable suspension ride height. The sensors on my mate's LS went bad last year and cost him over €700 each to replace (there are two on the LS)

[Chris Dance]

Check this link out:

http://www.toyotapartsoverstock.com/showAssembly.aspx?ukey_assembly=484019

[timberwolf]

According to the repair manual (American), the rear height level sensor is used with HID head lights.

As all UK spec Gen 2 only have halogen head lights, does the sensor do anything useful?

Is this one of those occasions where the UK spec differs in that we may have got self-leveling halogen head lights?? EDIT: Just looked at the Gen 2 brochure specification under Lights "Electronic headlamp levelling". I didn't know that! (Of course brochure specs can be wrong!)

[kithmo]

It looks to me like a rear load sensor that electronically controls the brake force distribution to the rear wheels via the ABS unit, allowing more force to the rear when the vehicle is low and hence loaded. If the link is broken it could be the reason why your rear discs are corroded (less use).

[Burma Sauce]

If you've got time on your hands, you might be able to repair your sensor - I did with my LS400 when I realised how expensive the replacement was!

[Terry953]

Then I get told that the 'electronic height sensor' has failed due to corrosion (a link arm has snapped) So, who can tell me what an electronic height sensor is? and what does it do? and how much do they cost? The only height sensors that I know of are on Lexus LS430's, and they control the adjustable suspension ride height. The sensors on my mate's LS went bad last year and cost him over €700 each to replace (there are two on the LS)

Being an Auris type I don't wish to trample over Prius subjects, or appear 'OFF TOPIC' as I've been accused of - but I beg your indulgence over this issue and hope to provide some clues.

My back ground is HVG's, but back in the early 70's HGV's and their trailer braking systems employed a rather crude pneumatic braking valve to regulate the max braking pressure to the rear brakes depending on the load on the vehicle, to prevent the wheels locking up and skidding.

It was called the LOAD SENSING valve.

A mechanical linkage attached to the axle would deflect according to the chassis load and position an air proportioning valve that would regulate the max pressure to the wheel brakes.

During routine servicing the physical condition was examined and during the 'HGV' MOT the operation was checked on a rolling road with a weight simulator.

Surley 40 odd years on you are not suggesting that this crude and vunerable mechanical system is employed on our state of he art Hybrids - and if so why isn't it subject to regular testing??

Any failures should have been flagged up before 70,000 miles !!!

[Terry953]

Then I get told that the 'electronic height sensor' has failed due to corrosion (a link arm has snapped) So, who can tell me what an electronic height sensor is? and what does it do? and how much do they cost? The only height sensors that I know of are on Lexus LS430's, and they control the adjustable suspension ride height. The sensors on my mate's LS went bad last year and cost him over €700 each to replace (there are two on the LS)

Being an Auris type I don't wish to trample over Prius subjects, or appear 'OFF TOPIC' as I've been accused of - but I beg your indulgence over this issue and hope to provide some clues.

My back ground is HVG's, but back in the early 70's HGV's and their trailer braking systems employed a rather crude pneumatic braking valve to regulate the max braking pressure to the rear brakes depending on the load on the vehicle, to prevent the wheels locking up and skidding.

It was called the LOAD SENSING valve.

A mechanical linkage attached to the axle would deflect according to the chassis load and position an air proportioning valve that would regulate the max pressure to the wheel brakes.

During routine servicing the physical condition was examined and during the 'HGV' MOT the operation was checked on a rolling road with a weight simulator.

Surley 40 odd years on you are not suggesting that this crude and vunerable mechanical system is employed on our state of he art Hybrids - and if so why isn't it subject to regular testing??

Any failures should have been flagged up before 70,000 miles !!!

[timberwolf]

Interesting. I'm unconvinced it has anything to do with the braking system. If it was a sensor to regulate the braking force - I would think the system could work out when the load stopped changing, I think it ought to under braking as the weight shifts forward? and thereforeif it were to do with braking there should have been a warning triangle and DTC thrown.

I'd go back and ask the dealer what it is for, ask them if there had been any DTC codes etc. The numpty behind the desk will probably try to make something up if they don't know though.

[Terry953]

Interesting. I'm unconvinced it has anything to do with the braking system. If it was a sensor to regulate the braking force - I would think the system could work out when the load stopped changing, I think it ought to under braking as the weight shifts forward? and thereforeif it were to do with braking there should have been a warning triangle and DTC thrown.

Absolutely timber wolf, with these modern abs/ ant-skid control systems I understood that the deceleration rates from individual wheels are monitored and if it is sensed that a wheel was decelerating to fast i.e. approaching a skid situation, braking force to that wheel was reduced regardless of chassis height or load.

No doubt the modern HGV solution is very similar but I have been out of touch for a few years now.

I'll vote for the headlight levelling idea, seems the best suggestion yet - but hey! - it's an expensive way to align your headlight beams !!!

[Chippy01]

Well guys, I crawled under the back of the car today to take a look myself.

Sure enough, there is a small box (about matchbox size) with two link arms coming out of one side, and wiring attatched to the back.

One of the link arms has ball and socket joints on each end, (one end fixes to a bracket on the chassis and the other is joined to the other arm) and this is the arm that has snapped. The ball and sockets are siezed solid and the other arm which attatches to the box won't move either.

[kithmo]

The Height control sensor is for the park assist system.

[Terry953]

The Height control sensor is for the park assist system.

Functional explanation please ????

[Chris Dance]

I have never used park assist except for once on my previous Gen 2, It took me longer to set it up than to park manually.

If anything on the car is suspension etc is broken I would definitely get it repaired paricularly if link arms are broken.

[timberwolf]

Does it look anything like this part on eBay?

http://www.ebay.com/itm/Toyota-Prius-Headlight-Height-Level-Sensor-Genuine-New-OE-OEM-/180944443990?hash=item2a21211a56&item=180944443990&pt=Motors_Car_Truck_Parts_Accessories&vxp=mtr

[ColinBarber]

The Height control sensor is for the park assist system.

Functional explanation please ????

The self parking feature of the Prius requires a height sensor to compensation for a change in vehicle height (rear passengers, load in the boot etc). Without it positioning the parking area using the rear camera display would be offset against reality.

[Chippy01]

I have never used park assist except for once on my previous Gen 2, It took me longer to set it up than to park manually. If anything on the car is suspension etc is broken I would definitely get it repaired paricularly if link arms are broken.

That would be my thoughts too.

It would certainly be picked up at the cars' next NCT (MOT) as it's plainly visible when under the car.

[Chippy01]

Does it look anything like this part on Ebay?

http://www.ebay.com/...ssories&vxp=mtr

It does look similar to that part on E-Bay.

But do our Gen 2's T-Spirit's have self levelling headlights? If so, why do I have a headlamp levelling wheel on the panel under the steering wheel?

[kithmo]

The Height control sensor is for the park assist system.

Functional explanation please ????

The self parking feature of the Prius requires a height sensor to compensation for a change in vehicle height (rear passengers, load in the boot etc). Without it positioning the parking area using the rear camera display would be offset against reality.

What he said ^

[kithmo]

I have never used park assist except for once on my previous Gen 2, It took me longer to set it up than to park manually. If anything on the car is suspension etc is broken I would definitely get it repaired paricularly if link arms are broken.

That would be my thoughts too.

It would certainly be picked up at the cars' next NCT (MOT) as it's plainly visible when under the car.

Nothing to do with the car's suspension or roadworthiness, it's for the park assist.

If you never use it why fork out the expense to replace it ?

Can't the arm or link be fixed/welded/bodged and joints freed up ?

I think I'll grease mine before it siezes.

[ColinBarber]

But do our Gen 2's T-Spirit's have self levelling headlights? If so, why do I have a headlamp levelling wheel on the panel under the steering wheel?

No they don't, only electronic levelling via the adjustment wheel on the dashboard. This sensor isn't for, or isn't only for, self-levelling lights, it is for the park assist function.

It is only HID headlights that require by law automatic self-levelling and washers.

[timberwolf]

The thumb wheel on the dashboard is another feature that I wasn't aware of or I have forgotten. I suppose it is possible that the head light leveling function has two inputs, one manual and one automatic, but I think that less likely.

I use part of the assisted parking i.e. the reversing camera and electronic lines superimposed on the image - I really like the lines and I understand some reversing camera systems do not have them. I guess the height level sensor input is used to control where the lines are superimposed on the image, in a similar way that the direction of the front wheels changes the arc lines displayed on the screen?

[johalareewi]

If you never use it why fork out the expense to replace it ?

Things on a car that don't work even if you don't use them can cause the car to fail an MOT.

[Chippy01]

kithmo

It looks to me like a rear load sensor that electronically controls the brake force distribution to the rear wheels via the ABS unit, allowing more force to the rear when the vehicle is low and hence loaded. If the link is broken it could be the reason why your rear discs are corroded (less use).

ColinBarber

The self parking feature of the Prius requires a height sensor to compensation for a change in vehicle height (rear passengers, load in the boot etc). Without it positioning the parking area using the rear camera display would be offset against reality.

Curiosity got the better of me today and I went back to my service agent.

Both kithmo and ColinBarber are correct.

(From my service manager) - "Although it is linked to the Park Assist system, it's primary function is to send 'load info' to the braking system, so that it knows how much braking pressure to assign to each wheel/axle, and is fitted to all Prius."

That being the case, if it's controlling the brake force it's something that will have to be fixed, sooner rather than later.

[timberwolf]

You can't be at any risk otherwise your dealer was negligent in allowing you to continue driving a car that they know has a defect in the braking system?

[kithmo]

I know I said it looked like a brake load sensor but upon further research I found no mention of it in the braking system components in the repair manual, I think the dealer is after your money