I asked for help over at tunerless Ecotec forum on Facebook. Billy is a mod over there.

 

Billy is DropDead here, maybe Goaliemo elsewhere

 

Billy is I.
aka goaliemo.
Jerama is bonstock. I don't think his car had cruise.
This is never anything i toyed with as I like to perk em up to make em scoot vs fuel economy.
We shall see if jerama chimes in.

 

Hi there! Figured I’d drop in and offer what information I had and ask questions. So from my understanding the Vue, Ion, and Cobalt take a reading from the output shaft speed and then its decoded by the BCM which applied a correction factor for tire size and such and you get your vehicle speed, which is why your speedometer works fine after doing the cobalt transmission. It worked perfectly in my Ion too. Have you tried using cruise in any gear other than fourth and fifth? I suspect that what’s throwing off the cruise is the fact that the gear ratio in fifth is different with the Cobalt transmission (or internals as you said) than with the Vue transmission. Fifth in the Vue transmission was .81 and the Cobalt transmission was .69, so you changed more than just the final drive ratio and the Vue PCM is still looking for that .81 fifth gear which you no longer have.

 

Yo dude!

Long time no forum post.
Glad you have not lost your ionicity, as it were.
He said 4th is the only gear in which cruise works.

 

That is correct. Only 4th gear is functioning.i did try disconnecting the speed sensor for informational purposes and the car stalled after a few miles and the cruise/shift lights didn’t work at all as suspected.

i have contacted EFL live, HPTiners and a few others with no hope that the vue PCM would be opened up to allow tuning. I did find a few standalone systems that might work but for one small issue I don’t think it’s worth it.

i am all about making this work but not into spending country weekends swapping harnesses and computers.

if there is a way to possible flash the BCM with a different setting or just trick the BCM someway that would be idea.

I am open ears to trying something different.

the car is so perfect now. 70-75mph and it’s under 2500 rpm.

 

Okay, the following is one of my standard mental wanderings. This one may actually lead somewhere so bear with it till you get to the end. It's train of thought. That's how I think, so you new guys will just have to deal with The annoyance
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It's either trick the BCM or modify the signal going to the cruise, which certainly has to be processed before it gets there. I always blindly assumed that, for pretty much any vehicle, the speedometer was driven off of a different sensor than the one used as part of controlling the cruise---or at least a differently processed version of what goes to the cruise.

Speed has no direction to it.
Velocity does. It is a vector quantity with amplitude and direction. I've always assumed that cruise control included the velocity and rate of change in velocity (acceleration). Allows the system to detect not just the velocity, but whether it is increasing or decreasing which will then likely require the cruise to request either less throttle or more throttle.

Then the whole system is averaged and damped so that the cruise is not jacking the speed all over the place. I don't know if the sensors that determine the levelness of the car are involved, but I suspect they are.

So I'm thinking if the output shaft is sending the signal, it's probably just reduced by some factor of voltage in order to drive the speedometer.

However, for controlling the cruise, you would have to figure out what it is sending to the BCM AND what the BCM is doing to it before it passes info to the cruise, The frequency and waveform.
I'm trying to think of how you trick the BCM into thinking the gear ratio is what it expects to see, which I think is equivalent to dividing the actual frequency coming from that sensor by the ratio of gears old to new for third fifth etc.

Frequency is not a simple quantity to transform. There are frequency division circuits but that is the hard way.
WAIT
Maybe the output shaft sensor voltage is out of range high for 5th gear and out of range low for third gear. The key to checking this would be to monitor the output speed sensor V with a scan tool as you drive in the different gears. I suspect below and above a certain voltage level, the BCM doesn't know what it's looking at and just ignores it.

I think it's worth a looksee

I'm surprised you don't get gear ratio error codes thrown in general, but I suppose that's a good thing that you don't.

There has to be a description of what that output shaft speed sensor signal is and the acceptable voltage range recognized by the BCM. I would think it would be an FSM for the Vue.

Anyone out there have one?

 

I’ve gotta ask, have you driven it enough to know what kind of mileage it’s getting with the Cobalt transmission? Yours is a swap I’d always thought about doing

 

I drive 100% city. Stock I was get 18-19ish. With this swap as it is I’m getting 21-22 city. I am more than positive correcting this issue would help. I also did brakes and suspension at the same time and i believe I have a slight binding of my caliper. I would say it’s safe to say I could end up getting 15-25% better city fuel economy but really it’s HWY that would be the key. Stock I was revving at 3kplus at 65 not I’m around 2-2100 which is huge.

 

the tech 2 didn’t have much info to supply. The amount to play with from the tech 2 in the vue is pretty bad. I am thinking you’re on the right track. I think looking into reflashing the BCM with cobalt specs for the vue would be the easiest way. I contacted a few companies to see if they can modify the flash they send down and if they are worth giving it. Shot. I wouldn’t find it hard to believe it’s also messing with fuel economy and possibly give me a little better drivability. I drives just fine but like I said in the first post 2nd gear low rpm is a little weird so the computer is definitely confused a little. Not enough to cause any big issues just not 100%