RX400h front parking sensors

[rynd2it]

On 4/29/2017 at 2:40 PM, cachaciero said:

Just a thought, I have been looking at fitting third party after market sensors to my RX400H, this in turn has led me to research CAN bus add ons which will enable the sensors below 5 mph AND disable them if the Parking Brake is set so do the genuine Lexus ones work the same way? do you need the parking brake set to kill the front sensors?

Sorry for the delay - been away on vacation. You raise an interesting point - if the after market "Can bus" sensors can detect speed and gear position, why can't my Lexus ones?  The Lexus ones (front) are on constantly below 10kph and regardless of gear selection or parking brake. I'd be interested in the wiring diagram and/or instructions for yours

David

[cachaciero]

On 11/05/2017 at 6:06 PM, rynd2it said:

Sorry for the delay - been away on vacation. You raise an interesting point - if the after market "Can bus" sensors can detect speed and gear position, why can't my Lexus ones?  The Lexus ones (front) are on constantly below 10kph and regardless of gear selection or parking brake. I'd be interested in the wiring diagram and/or instructions for yours

David

Ah! This was a "research" exercise when looking into fitting after market sensors. The vast majority of cheap and cheerful after market sensors just look at the reverse light line, and have a manual switch to control the front sensors. Now for me that really was a cowboy approach (but cheap :-) I knew that all the data one could possibly need would be available on the CAN system if one could access it.

Further investigation revealed that there are available decoder boxes which connect onto the CAN bus and process the data giving discreet output lines for Reverse, Parking Brakes set and a  <5mph Flag. With such a box one could choose whatever combination of conditions to activate the sensors, my choice would be all sensors on below 5mph and OFF when Handbrake set and forget about the reverse condition.

However the cost of such a box was in the order of a 120 quid which I decided was a bit much for a 10 yr old car so when I found a set of sensors that activate the rear and two front corners in reverse and the fronts for 30 seconds after coming out of reverse I decided that that was a reasonable compromise, so in answer to your question I do not have any schematics :-(

The  Lexia  TPA800 does not connect to the CAN bus so does not have access to the data which is available on it. The TPA800 connects to a speed signal which is a pulse signal proportional to speed used by the GPS amongst other things, and the reverse light switch. (At the time of my previous comment I had not looked in detail at how the TPA800 connects I assumed that given the price Lexus would have done the job properly...silly me.)

Now I deduce from that, that within the TPA800 there is some computation of the speed signal and I would expect this to be able to work on the basis of activating the sensors when the speed is below a certain threshold and deactivating them at zero, however that is a guess on my part.

The speed pulse signal is I believe derived from the wheel speed sensors on the AntiSkid system so if my guess on how the TPA800 works is true then maybe if there was a noisy sensor such that at zero wheel rotation it was generating enough noise to correspond to say 1mph then the parking sensors may not turn off, just a theory.

tonyd

 

[rynd2it]

That's a great piece of research. Consensus seems to be that the front sensors are designed to be active when stationary and I plan on fixing that with the relay from the  'D' as soon as I have time to figure out where to connect it.

Cheers

David

13 hours ago, cachaciero said:

Ah! This was a "research" exercise when looking into fitting after market sensors. The vast majority of cheap and cheerful after market sensors just look at the reverse light line, and have a manual switch to control the front sensors. Now for me that really was a cowboy approach (but cheap :-) I knew that all the data one could possibly need would be available on the CAN system if one could access it.

Further investigation revealed that there are available decoder boxes which connect onto the CAN bus and process the data giving discreet output lines for Reverse, Parking Brakes set and a  <5mph Flag. With such a box one could choose whatever combination of conditions to activate the sensors, my choice would be all sensors on below 5mph and OFF when Handbrake set and forget about the reverse condition.

However the cost of such a box was in the order of a 120 quid which I decided was a bit much for a 10 yr old car so when I found a set of sensors that activate the rear and two front corners in reverse and the fronts for 30 seconds after coming out of reverse I decided that that was a reasonable compromise, so in answer to your question I do not have any schematics :-(

The  Lexia  TPA800 does not connect to the CAN bus so does not have access to the data which is available on it. The TPA800 connects to a speed signal which is a pulse signal proportional to speed used by the GPS amongst other things, and the reverse light switch. (At the time of my previous comment I had not looked in detail at how the TPA800 connects I assumed that given the price Lexus would have done the job properly...silly me.)

Now I deduce from that, that within the TPA800 there is some computation of the speed signal and I would expect this to be able to work on the basis of activating the sensors when the speed is below a certain threshold and deactivating them at zero, however that is a guess on my part.

The speed pulse signal is I believe derived from the wheel speed sensors on the AntiSkid system so if my guess on how the TPA800 works is true then maybe if there was a noisy sensor such that at zero wheel rotation it was generating enough noise to correspond to say 1mph then the parking sensors may not turn off, just a theory.

tonyd

 

 

[cachaciero]

7 hours ago, rynd2it said:

That's a great piece of research. Consensus seems to be that the front sensors are designed to be active when stationary and I plan on fixing that with the relay from the  'D' as soon as I have time to figure out where to connect it.

Cheers

David

 

A relay connected to D ...(rive?) you might have a problem doing that I would have to go back and delve into ,the wiring but pretty sure that the Gear Selector is it's own ECU connected to the CAN bus so there will not be anything to connect to :-).

Tonyd

[rynd2it]

2 minutes ago, cachaciero said:

A relay connected to D ...(rive?) you might have a problem doing that I would have to go back and delve into ,the wiring but pretty sure that the Gear Selector is it's own ECU connected to the CAN bus so there will not be anything to connect to :-).

Tonyd

I bow to your superior knowledge - however I was just looking at the main wiring diagram and it shows a yellow wire connected to S35 Shift Lever Position Sensor from the ECU position 9. I was assuming I could splice into that wire (I do have some experience with auto wiring) and that would power a relay which in turn would connect/disconnect power to/from the front loom where the on/off toggle switch is.

Please correct me if I'm all wrong

David

[cachaciero]

15 hours ago, rynd2it said:

I bow to your superior knowledge - however I was just looking at the main wiring diagram and it shows a yellow wire connected to S35 Shift Lever Position Sensor from the ECU position 9. I was assuming I could splice into that wire (I do have some experience with auto wiring) and that would power a relay which in turn would connect/disconnect power to/from the front loom where the on/off toggle switch is.

Please correct me if I'm all wrong

David

Please! Please! don't ever think I have superior knowledge on anything and least of all the Lexus which I have only had for six months :-) I don't even have a complete set of schematics and none of the Training Material which I am sure is available to their Techs.

Currently for areas  of interest I have to go onto the Lexus Support site and wade through bits of that trying to find info on the things which are of interest. So far I have not had a need to look in detail at the gear selection side so I don't have all the info on this area of the car. As regards the gear selector something I saw / read somewhere makes me believe that it works the way I said it does BUT I could be wrong. The gear positions are displayed on the instrument panel and for sure that data comes from the network, doesn't mean to say though that there isn't a discrete wire for each position directly from the gear switch though I can't see why they would need to do that. If you like send me a copy of the schematics you have (saves me time and money!) and I will have a look and tell you what I think.

However my gut feel is that is that it will be easier to purchase one of the available decoder boxes that hook onto the can bus and give the discreet outputs you require, prices seem to range from about 50 to 150.00 depending on the number of outputs.

Out of curiosity why don't you just  use the switch to disable the front sensors?

regards Tony

 

[rynd2it]

30 minutes ago, cachaciero said:

 

Out of curiosity why don't you just  use the switch to disable the front sensors?

regards Tony

 

Because it's a toggle switch and stays off until you press it again OR you restart the car :(

Here's the Shift Control schematic I was referring to

David

Lexus_Shift_Control.pdf

[cachaciero]

47 minutes ago, rynd2it said:

---cut--

David

Lexus_Shift_Control.pdf

O.K it doesn't work the way I believed it did, have to say I am a little surprised, it aint logical :-).

The next question is what are the o/p volts 12V....5v or something else and what is the switch? straight forward electrical contacts which may handle enough current to drive a relay or an optical or other semiconductor O/P which may have very limited current drive capacity, hooking a relay coil straight onto such an output could have disastrous consequences.

Bit more info required :-)

Regards Tony.

[rynd2it]

5 minutes ago, cachaciero said:

O.K it doesn't work the way I believed it did, have to say I am a little surprised, it aint logical :-).

The next question is what are the o/p volts 12V....5v or something else and what is the switch? straight forward electrical contacts which may handle enough current to drive a relay or an optical or other semiconductor O/P which may have very limited current drive capacity, hooking a relay coil straight onto such an output could have disastrous consequences.

Bit more info required :-)

Regards Tony.

When I get a round tuit (!) I'll take readings etc off the cables and measure cable sizes. I can use a very low current relay to drive a 12v circuit so I don't anticipate any issues. I'll let you know but it'll be a while.

David