Can we do this? (aka The DIY Cruise Control Thread)

[CTScott]

Originally Posted by Sir A.Y. Atoyot

You could install one of the aftermarket Rostra brand units, which doesn't attach to the steering wheel. Be prepared to pay lots, though.

Or you could add four momentary switches (On/Off, Set, Up, Down) to the dash like I am going to do to save on buying the stalk and on having to pull the airbag.

[Sir A.Y. Atoyot]

Originally Posted by CTScott

Or you could add four momentary switches (On/Off, Set, Up, Down) to the dash like I am going to do to save on buying the stalk and on having to pull the airbag.

Good luck with that - those functions on the stock switch work through resistors and involve the extremely expensive central engine computer (ECM). The resistors are the squiggly lines in the diagram. It's important to know the exact values to make it work right. A familiarity with Ohm's Law would help, too.

[CTScott]

Originally Posted by Sir A.Y. Atoyot

Good luck with that - those functions on the stock switch work through resistors and involve the extremely expensive central engine computer (ECM). The resistors are the squiggly lines in the diagram. It's important to know the exact values to make it work right.

Correct. The resistor values are:
216 to 264 ohms for one between resume and on/off
351 to 426 ohms for the one between set and resume
819 to 1001 ohms for the one between set and cancel

This is a standard way of having multiple inputs on a single wire.

[CTScott]

Originally Posted by PK198105

you realize CTScott is an electrical engineer right and Im a electrical engineering tech


BTW CTScott i was thinking the same thing about the switches except Im thinking of mounting them in my door armrest right above the handle, i will most likely canibalize the stalk and use jumper wires and a LED to show the status

I am soldering up a two button test rig right now. I have a Karate class at 8, so I am hoping to test on/off and Set on my way there...

[CTScott]

OK. My two button rig is connected. When I turn the ignition on and press my on/off switch the speedometer icon lights up. Now to throw on my dobuk and hit the road for the road test...

[IllusionX]

PK: if you are going to make yourself a new set of switches... don't cannibalize your stalk... sell it to me :)

[CTScott]

Originally Posted by PK198105

so you connected it straight to D3?

Worked like a charm!

I used tap splices onto pins 1 (blue) and 3 (brown) of D3.



My test setup consisted of 2 feet of 2 conductor cable going to two parallel switches. The first is the On/Off switch which connects directly to the two wires. The second is the Set switch and has a 660 ohm resistor on the CCS line from the first to it.



Here's the combination meter in the garage with the ignition on and the on/off button pressed once:


Here's the meter with the Set button pressed at 35 MPH (and my foot off the gas):



The Set button doubles as the - button, so each press would drop the speed by one MPH. When I pressed the On/Off button while CC was on, it would drop the lights and decelerate until I put my foot on the gas. So, at this point I have free cruise control (from parts lying around my office).

Now I just have to find some switches that I like to button it up...

[AlexNet0]

thats awesome, you should make a step by step how-to with a link to the resistors to use, I would actually prefer this way

[Sir A.Y. Atoyot]

Very tidy - congrats to CTScott on getting the first practical results out of this discussion.

I'm not an electrical engineer - just a licensed mechanic. I have an aversion to hacking into the wiring on a near-new car that's still on warranty, but I can see my way clear now to acquiring the necessary bits to do it right.

[AlexNet0]

Originally Posted by PK198105

Alex check if you have the wires in D3 otherwise you will need jumper wires

Will do tomorrow

[CTScott]

Originally Posted by PK198105

great news, although i suspect that you have factory installed wire going to AD4 junction box.

my turn but only after my exams lol. which switched you plan on running.

Have you checked to see if there is a wire leaving pin 15 of connector AD4? If there is, then tapping there wouldn't be any worse than tapping D3. Also, you only need that one wire, as the other just needs to connect to any ground point.

[CTScott]

Originally Posted by PK198105

if you look on page 105 of the EWD it says pin 6 for the AD4 box from D3.

That's correct. I was looking at the wrong blue when I typed that. When Alex checks his D3 connector (where I am 90% sure he'll just see the lonely horn wire), he should then check Pin 6 of AD4 to see if there is a wire there.

[CTScott]

Originally Posted by PK198105

the only PITA is that the AD4 box is under the dash near the windshield. But why would he only have the Horn wire, whats different from your Yaris?
did you get an extra option or what? The other thing is on mine i don't have the Cruise Icon, so i would need to McGyver a way to get a LED to light up when I turn on the cruise

I think that only 09 Liftbacks have the two additional wires in D3, as Sir A.Y. Atoyot's 08 didn't and neither did SodiumDuck's 08.

[CTScott]

Originally Posted by PK198105

cool, ill pop mine tomorrow and let you know if the 07 has it or not. how did you approximate the resistor values, because from the diagram the values given are for the total resistance , i.e each resistor adds to the other to create a final resistance depending on which switch is active. I.e cancel one takes all three resistors into consideration

The service manual gave resistance ranges from CCS to ground with each of the four switches pressed.

Resume picks up just the first resistor, so its resistor value is simply the value listed.

Set picks up the first two, so I subtracted the value for Resume from total resistance measurement with Set pressed to get the second value.

Cancel picks up all three, so I subtracted the value total resistance for Set from the total for Cancel to get the value of the third.

[CTScott]

Originally Posted by PK198105

ok thats logical , i wasn't sure about the 10k resistance when the switch is off. but i guess that's the "ECM impedance". so i guess we could use:

Standard values:
RES ---> 240Ohms
SET ---> 620Ohms
Cancel ---> 1600ohms
All these in 5% tolerance level or even 1%


NOTE: TO ALL ATTEMPTING THIS WAY MAKE SURE YOUR SWITCHES DO NOT HAVE A BUILT IN RESISTANCE OR THIS WILL CHANGE THE VALUE OF THE TOTAL RESISTANCE AND MAY CAUSE UNRELIABLE CRUISE CONTROL FUNCTION OR DAMAGE TO THE CSS PORT OF THE ECM

Those are correct if you wire the switches with the resistor in series with each. If you wire it per the stalk schematic they would be:

216 to 264 ohms for one between resume and on/off
351 to 426 ohms for the one between set and resume
819 to 1001 ohms for the one between set and cancel

By the way, you actually can't harm the EMC port with the wrong resistors, as the port can handle a direct short (as the on/off switch does) to infinite resistance (no buttons pressed).

[Creeper]

so with the switches option do we still have to take off the airbag or just the stearing column cover?

[devinlamothe]

Originally Posted by PK198105

The switches you will only need to take the steering column off and look for two wires from the D3 connector a blue one and a brown one. Now if you don't have these you will most likely need to attach at least one jumper wire to act as the OEM blue wire that goes from D3 to junction box AD4 which is located on the driver side near the windshield, thus you will have to take off the dash most likely (unless someone has an easier way of accessing this location)

Hopefully there is an easier way of getting there as I have no intention to take my whole dash off

I am going to be putting a new headlight stalk on tomorrow so I will check my '07 liftback to see if the wires are there.

[Creeper]

ill have to look next time i work on my car. when my projectors get here... also gotta try to do easy fix on my back bumper :( anyway ill check my 07 hatch when i can..