How to install a Cruise Control switch in 2004 Prius?

It sounds like you wish to DIY the installation. I suggest you obtain a subscription to the Toyota Europe techinfo website so that you can download the necessary info, like how to remove the steering wheel center hub without having the airbag blow up in your face, how to install the stop light switch on the brake pedal assembly, etc.
Toyota Service Information

Good luck.

 

Use this website to confirm Toyota part numbers. The list that you cited sounds good; at minimum that should give you a good start on the project.
http://www.toyodiy.com/

If you do a search you may find posts from other owners who have done the project and confirm their parts lists. Some posters, instead of replacing the brake light switch, use a normally-closed relay to provide the second set of contacts, that is controlled by the contacts on the existing switch. This is because the switch is not that easy to get to and replace. An interesting alternative to consider.

 

Breaking the ECU? The ECU already provides the cruise control function, there is just no switch to turn it on and set it. All the install does is connects a switch so you can turn on the function and set it, as well as adds the brake switch so that the brakes can turn off the function.


I'm not sure how difficult it is, but will be doing it within the next couple months. Sucks that the base model doesn't have the switch, but it looks to be an easy problem to remedy.

While we're at it, if you get the parts, can you let us know the cost of each?

 

Prius has multiple ECUs. The hybrid vehicle ECU manages the cruise control function. Pin ST1- is connected to +12VDC provided by the 7.5A IGN fuse, through a normally-closed switch. When the brake pedal is depressed this switch will open so that current flow is interrupted.

The same ECU also has pin STP which receives +12VDC provided by the 7.5A STOP fuse through a normally-open switch. When the brake pedal is depressed then 12VDC is provided to that pin.

The cruise control switch has several resistances within the switch that come into effect depending upon which function you select; ON/OFF, CANCEL, +RESUME, -SET. This switch is connected to pin CCS of the HV ECU. Based upon the resistance that pin CCS sees to ground, it can determine which cruise control function to implement.

 

Hi Jack,

I haven't needed to do this myself so I can't tell you how easy or hard this will be. As a new cable is on the parts list it might be necessary to interface the wiring into one of the existing cable connectors that plug into the HV ECU. Not sure whether the existing stop light switch socket will fit the new switch or not.

If you can't find first-hand accounts of this process written by other members who have done the job, then you'll have to download the repair docs so that you can provide them to your dealership technical staff and hope they can figure it out. Good luck.

 

The 'normal' (no cruise control') stop light switch is a single-throw normally-open switch, which closes when the brake pedal is pressed. The Cruise Control version is a double-throw switch, where one side is normally-open and the other normally-closed. As the pedal is pressed, the normally-open switch closes and the normally-closed switch opens.

The normally-open side controls the brake light as before; the HV ECU monitors both switches and checks that they produce consistent answers. If it detects that both sides are open, it deactivates cruise control because it cannot reliably detect that the driver has pressed the brake pedal - you wouldn't want the car to run away because the switch has failed, or the 7.5A STOP lamp fuse has blown, and that part of the car can no longer tell that you're trying to brake. Because this is a potential danger scenario, it logs DTC P0571 and the CRUISE light blinks. (There is a small allowance of time for the switch to actually switch over, but it's a fraction of a second.)

 

Yes, this is how the switch looks like in the 2001~2003. I believe it is the same for 2004. The white switch is double-throw and the black switch is single-throw.

There is a SSC-40L for the Brake Light Switch replacement: View attachment 40ltechn.pdf Perhaps you can show it to your dealer as to how to replace the switch?

 

Nope, I didn't come across any instructions for the 2004 yet. I only have the instructions for the 2001.

2001 Prius Cruise Control -- Intro

The 2001 is more complicated then the 2004 because the original steering wheel do not have opening on the cowl. Some owners either bought the new cruise control steering wheel at $600 or they just cut two holes into the cowl to accommodate the cruise control switch. I believe your 2004 already has the cutout on the cowl.

 

Hi Jack,

My post #2 provides you a link to the Toyota Europe techinfo site. If you plan to DIY I again urge you to download the relevant repair manual pages so that the airbag doesn't blow up in your face.