That could be useful as I am stuck at the moment, I found the relay can be wired either way it makes no difference still no start!

Cheers Andy

 

Is there a clear advantage to a push button start? Do you still have to insert the key? If so, how do you run ACC only? How will the drivers seat position before start if you don't insert a key? How do you bypass the security feature embedded in the key?

Thanks,

 

Bypassing the VATS is easy, just measure the resistance of the pellet and buy a precision resistor that value and hack it in. Cost about $1 at Radio Shack. Seems to me all you'd have to do is hack the button/relay in on the start circuit so the key would be in the ON position and you'd be mimicing the START. I need to study the schematic more-the BCM might need to know that the car started to do all it's magic (like move the seats/HVAC/lights and the like). Sure seems like a huge hassle for no real upside. The one in the picture at the top looks like a little weird to me. With the column lock issues and all, you might wire your way into having the car useless most of the time.

 

The whole thing is worse than that, since there needs to be a delay from key insertion 'till it's turned to acc, and "go" ends up resetting 2 of the circuits that are energized on ACC on top of energizing another 2 circuits for ignition. Yes, you can trick the VATS with a variable resistor (or, just a handy assortment from the rat shack), but that's one out of several things that have to fall in to place for the car NOT to think it's being stolen.

In my case . . . no keyswitch. Didn't need it, didn't want it, and since the car never sees the street, it's not a big deal. Also in my case, I built the CLB, clutch switch, and a provision for a 2nd master/start (read, for being able to turn the car over without having someone sit in the driver seat) all into the same module. It's more complex overall, but simplifies things in the cockpit for me.

For a street car, you'd still want to keep something in for security . . so yeah, you'd probably want to keep the key for something. What I'm trying to think of (from memory . . . since I think the details are on a HDD thats out for recovery right now) is if there's an easy way to bypass all the cr@p that GM threw in, or simply energize one or two out of the 5 circuits that comprise the ignition.


Still looking for the details, but it may be a few days.

 

The way these system are set up ....

You insert key and turn to the ON position. This takes care of VATS and other issues. Then you reach down and push the START button instead of turning the key to the START position.

To most people, it is a "bling" item ... instead of twisting key to start, you reach over to a seperate button to perform the same function.

In the OP's case, apparently the wiring for the switch is incompatible with the C5 electrical system. The system to start the engine is quite complex in a C5 ... it's not like the old days where you are simply providing power to the starter motor. The PCM, for example, expects certain "messages" from the BCM before it will allow the car to be started/driven. The BCM controls the SECURITY function of the car, and if it is "happy" with the start sequence (VATS is correct, doors were unlocked correctly, etc.) then the BCM sends the PCM a "password" indicating that it is OK to provide the engine with fuel. So, for example, if you "hot wire" a C5 and provide power to the starter and spark plugs, if the PCM hasn't received the password from the BCM, it will turn off the fuel injectors, shutting down the engine as soon as you try to drive away.

 

Ok. so it sounds like in reality, this would just be cutting into the ignition system on a car that already has the potential to be an electrical nightmare.

 

That is a pretty good way to put it ....

 

Yeh sounds complicated! If it can't be done then I just leave it and carry on turning the key.

I had the switch left over from when I did the Z28 as I fitted one with a blue led halo light around the switch then I got an S2000 switch off Ebay in the USA about half the price of buying one in the UK!

As you say certain things like Vats are taken care of by me putting in the key and turning to the on position what I need to know is what happens when I do the last turn of the key! what signals are sent to the BCM or PCM?

 

Maybe it will help if you think of turning the key to the START position as a "request" to the BCM and PCM to start the engine. YOU aren't actually completing a circuit that will start the engine UNLESS the BCM has decided that all is OK, and the BCM closes the "Theft Deterrent" relay.

If it helps further, on the C6, when you "touch" the start button you can immediately let go and the engine will crank until it starts (or the PCM stops cranking because it wants to protect the starter in a no-start situation). You have "requested" engine start, the computers actually start the engine.

Another example, on my g/f's Pontiac GP/GXP with the LS4 engine (V8) when the key is turned to START there is about a 1/2 second pause while the computers go through the start sequence and then the engine starts cranking.

As I mentioned earlier, the BCM has to send a password to the PCM for the car to be diven. GM realized that it might be possible to substitute a BCM into the car that has been "programmed" (or wired) to ignore the anti-theft measures. So every time the BCM sends the password to the PCM, they then agree on a new password, so if you substitute another BCM in, it won't have the correct password. There is a procedure to get a new BCM to re-synch with the PCM on a password, but the procedure is time based and takes a minimum of 30 minutes to complete ... which most thieves aren't gonna sit around and do ....

I suspect there are other "safeguards" built into the start system that, for obvious reasons, GM doesn't document. For example, note in the wiring diagram there is a "lamp test" position the key passes on the way to START. It's possible when the IPC does the lamp test it sends a message to the BCM, and if the BCM doesn't get that message, it assumes a "theft" start and won't complete the start sequence.

You may be able to re-wire around all this (maybe permanently bypass the theft deterrent relay), but it probably isn't as simple as just inserting a relay ... as you have unfortunately discovered.

 

Yeah, but it is "simple" enough that it could be done with 2 NO and 2 NC relays. (again, from memory) . . . everything comes down to your individual version of "simple". Ditto, the complexity in the ignition comes down to how much you want to keep / replace of the original components.

There's no logic in the C5's keyswitch, so everything else comes down to knowing what happens when. The good news is this isn't rocket science . . . OTOJ, it just isn't easy.

 

here is how you need to wire it assuming you still turn the key to the on position.

 

First I want to comment on this post. This time around people are actually being constructive and helpful. Last time all it was was a bunch of people saying why it wouldn't be a good idea. So excellent to keep it going like this.

What about making a mechanical device that would use the actual key cut short. Push it in and it turns the key? Use an alarm system with a cut off device for security. Hit your remote get in and push the mecahnical device that turns the key, push it again and it turns off, maybe goes to Accessory? Just to throw it out there. That way no wiring issues (except the alarm) Now need the mechanical people to step in instead of the electricals...

 

I will try that this week, the only thing I can see different than what I have tried so far is you are using the same 12v+ to power the switch and the relay.

Is this a set up you have tried and it works or is this how you think it should be wired?

This is because I did a search and saw all the why would you want to do that for posts you still have to put the key in and turn it on!
so I ask for people not to post these type of replies thankfully they listened.

So speaking as someone who did this mod to there 99 Z28 and it was cool a heck I think it is definately worth doing.

Trouble is I thought it would be same wiring as the Z28, by it turns out the C5 Vette is well protected from thieves! Not that what I am doing makes the car any easier to steal you still need the right key with te correct chip!

 

That will definitely work. You can test it by turning your key to the run position and applying 12v to the yellow wire. If you are touching wires together there will be a spark - since you are closing the connection to the starter solenoid.

 

Hello,

Please, has anyone succeed in installing an start engine button in the Corvette c5? I want to maintain the key, and my idea is to put the key in on position, and then push the button to run.

I have checked the yellow cable has electric power only at the moment when the key is turned to run the car.

I have bought a start engine button. To the input I have connected red cable 12 V. To the outside I have connected the yellow cable. So when the button is pushed I have checked 12V are transmited to the yellow cable. But the cad doesn´t run. Any idea? Please, anyone succeeded?

Thanks
Best regards

 

interesting! did you use a C6 push button? any pics?

 

No, I am using a push button I bought on ebay. I attach some photos. Please, anyone has any idea why it doesn´t work?

Thanks!!!!!

 

When I was trying to make a push button system I found that the car wouldn't start unless the switching procedure was the same as found in the ignition switch. There are four power circuits controlled in the following order: When the key is moved to the ACC position the Accessory circuit is turned on. When the key is moved to the RUN position both the Ignition Run and Ignition Start circuits are turned on. As the key is turned to the start position both the ACC and Ignition Run circuits are turned off but the Ignition Start circuit is left on. When the key is in the start position the Start circuit is turned on and the starter is powered as long as the brake or clutch safety switch is closed. When the key is released an internal spring returns the key to the RUN position which turns off the starter and turns on both the ACC and Ignition RUN circuits. When I switched on the ACC, Ignition Run and Ignition Start circuits with separate switches and then tried to switch on the START circuit the car wouldn't start. Most cars use this sequence so that all nonessential loads are turned off to provide the most power to start the car. Have you ever noticed when starting a car in the rain with the wipers on they go off as soon as the starter is engaged and then go back on when the key is released? This starting procedure seems to be linked to the computer on the C5. Similarly, if you try to start the car when the engine is already running, the computer won't let that happen.

 

You've been a member for 15+ years and this is your first post?!

 

No, the computer unlogged me and I forgot my password so the administrators changed my user name yesterday.