^^ why does the Ecu need a wire from the brake switch?

 

It doesn't.

 

It uses it for the IACV. pressing the brakes uses vaccuum pressure from your plenum. The plenum pressure drops/rises, depending on if you consider atmospheric or gauge pressure), IACV engages to correct the idle to prevent the engine from stalling.

Try this simple test while your engine is idling (means you're not moving/on throttle). Depress brake pedal for a while, and let off, see the idle rising? That's the use for the brake switch. Helps stabilize the idle. The a/c and power steering does this as well.

 

well then why is there an pin for the brake switch? :S

im just wondering cause when i press my brake pedal, the RPM rises from ~1000 to ~1400 and if i press it twice the RPM goes up to ~1800...

and then when i looked at a diagram, it showed that the green/white wire should be connected to the ecu on D5...

i just can't see what it should use the brake switch for? unless it is for cruise control? (which my car doesn't have)

 

The answer is above lol.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by shiroitenshi &raquo;</TD></TR><TR><TD CLASS="quote">It uses it for the IACV. Much like any accessories on your car, pressing the brakes uses vaccuum pressure from your plenum. The plenum pressure drops/rises, depending on if you consider atmospheric or gauge pressure), IACV engages to correct the idle to prevent the engine from stalling.

Try this simple test while your engine is idling (means you're not moving/on throttle). Depress brake pedal for a while, and let off, see the idle rising? That's the use for the brake switch.

</TD></TR></TABLE>

alright didn't know that..
but if the wire isn't connected it shouldn't rice the way it does when i depress the brake pedal.. right?

 

I'm sure they added the pin for possible uses, but they didn't implement them. Simply giving the pin +12 (It's a +12 input) does nothing noticeable. What actually causes the idle to go up is the load put on the electrical system from the brake lights and, as shiro mentioned, the change in vacuum. Try it.

The closed loop idle system is always going regardless of inputs activated.

The cruise control is a separate unit from the ECU.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by menthos &raquo;</TD></TR><TR><TD CLASS="quote">
alright didn't know that..
but if the wire isn't connected it shouldn't rice the way it does when i depress the brake pedal.. right?</TD></TR></TABLE>

You won't notice any difference.

 

Not sure. Never tried with it disconnected.

But since the brake does use the pressure from the intake manifold plenum, it could be that it occurs naturally due to the vaccuum effect.

But from what I've played and read about with on my honda, that's the primary function of the brake switch.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by HRTuning &raquo;</TD></TR><TR><TD CLASS="quote">I'm sure they added the pin for possible uses, but they didn't implement them. Simply giving the pin +12 (It's a +12 input) does nothing noticeable. What actually causes the idle to go up is the load put on the electrical system from the brake lights and, as shiro mentioned, the change in vacuum. Try it.

The closed loop idle system is always going regardless of inputs activated.

The cruise control is a separate unit from the ECU.</TD></TR></TABLE>
why should the load on the electrical system matter on the RPM?
then it should be a bad ground spot or something? my battery/generator should make enough power

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by shiroitenshi &raquo;</TD></TR><TR><TD CLASS="quote">Not sure. Never tried with it disconnected.

But since the brake does use the pressure from the intake manifold plenum, it could be that it occurs naturally due to the vaccuum effect.

But from what I've played and read about with on my honda, that's the primary function of the brake switch.</TD></TR></TABLE>
well i think that the RPM rises as soon the switch are activated, but not sure.. have to test that...
if the rpm rises as soon the switch are activated, it couldn't be the vaccuum, because the brake is first activated a bit lower, right?

 

No the RPM does not rise as soon as you engage the switch, I'm sure of that, it rises after you let off. But I do notice that the IACV engages when I depress the brake pedal. On old cars, upon depressing the brake, the rev drops a little, but as you've noticed on honda that works perfectly fine, it is not present. Then again, that could be the IACV doing it's thing on it's own. I did remember I read some technical article about it, and that the brake switch does do something with IACV, but I'm hazy as to the details after so long.

But I don't think honda would put something redundant as a blank 12V input.

In which case, the other explanation would be the same as why they had empty sockets for OBD-0 and OBD-1 systems, for chipping and datalogging purposes. I noticed that the CN2 port for Crome and Hondata seems to read the 12V input when datalogging.

For OBD-2 cars, I think that is a required feature to meet OBD-2 compliance. I think I've read it in passing before.

 

Guys, this was thoroughly tested. Read my above statements.

There's a thread on the NepTune forum that has more info about this topic where one of my customers actually did this test and reported the same results.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by HRTuning &raquo;</TD></TR><TR><TD CLASS="quote">Guys, this was thoroughly tested. Read my above statements.

There's a thread on the NepTune forum that has more info about this topic where one of my customers actually did this test and reported the same results.</TD></TR></TABLE>

yeah i just tested it too... didn't see any big difference... the rpm still rises about 400RPM when i press the brake pedal

it must be a vaccuum problem, cause there is no reaction when i only press the pedal to the point where the switch engage...

 

and therefore it's a great input to use for other functionality, if you have something like NepTune, eCtune, or Hondata.