Hacking the Saturn Cruise Control ...
 

Hello -

I was staring at my Saturn's cruise control the other day when I noticed that the actual cruise control module under my dashboard has a six-wire connector leading into it. I went to my Haynes Repair manual and looked at the electrical diagram :

Attachment 702

It seems to me that if I can figure out how the MOVE and WOT/IDLE signal wires behave, I could suppress the cruise control's desire to open the throttle when going uphill.

The main benefit is that I think I can get the cruise control cutoff for the BRAKE and the CLUTCH for free, because I would leave those wires connected.

Detail : Notice that the "brake wire" input to the Cruise Control goes directory to the CC Module and not through the ECU/PCM. That implies to me that Cruise Control Module will ignore the ECU/PCM signal when it gets a signal from the brakes. However, the electrical diagram could be misleading me by leaving information out. That is to say, the ECU/PCM must also be getting the brake signal, so it could also be changing the MOVE and WOT/IDLE signals when the brake is applied.

The bad part is that I could (as usual in these things) make the ECU/PCM go crazy and throw a code.

CarloSW2

Wait one dang minute, are you telling me that there is a seperate module for the cruise? And I just need to fake out that light blue wire?!? Dang, why didn't you say so sooner :)

history, since my trans swap, the gear ratios in the transmission do not match what the computer is expecting, so the cruise control thinks the clutch is slipping and it won't engage. Saturns have some peculiarities to them, But I still like 'em :)

In looking at the schematic the direction of those signals seems backwards from what I'd expect. Take that as an indication I haven't the first clue what I'm talking about here. :rolleyes: Apply the appropriately-sized grain of salt and reasoned caution as you read what I'm about to type. :)

Based on general interface knowledge, here's my off-the-cuff guess:

"MOVE" is a change/step indicator. It indicates when the speed needs to change (or "is changing" if I have the direction backwards). It could be a pulse representing a discrete step, a proportional voltage (unlikely), or a level change that stays until the desired speed is reached. Or something else that hasn't occurred to me yet.

"WOT/IDLE" is the direction for the change. It indicates if the speed needs to go up (towards WOT) or down (towards IDLE), or maybe it indicates which side the error is on (in which case the sense would be reversed).

If the above guesses are right, then the state of the WOT/IDLE line would likely be ignored as long as MOVE wasn't asserted. Also if they're right, then it seems just intercepting the MOVE line and substituting the "all is right with the world" state would cause the cruise control to leave everything alone.

Disclaimer: I know zip about cruise control electronics and even less about Saturns. It would be foolish to rely on any opinions I offer on this subject without testing and verifying. I am not responsible for any damage you do to your cruise control, your car, yourself, any other vehicles, persons, roadways, property, hedges, or small woodland animals. :p

Rick

EDIT for clarification: The above guesses would make a lot more sense if the RASC IN line from the user control went to the CCM and WOT/IDLE and MOVE were inputs to the PCM. Coming out of the the PCM as they are is what confuses me -- where does the CCM even get the chance to control anything? Is there another plug/harness on the CCM that connects to the ECU?

I think the WOT/IDLE signal comes from the PCM to tell the CC to "stop trying to adjust the speed now, you are at the limit of travel".

skewbe -

Here is the CC module that receives the 6 wires :

Attachment 706
EDIT : This picture is from "Mitchell Repair CD" or equivalent.

It's really simple. The "Cruise Adjuster Cable" is attached to the accelerator pedal, way above where you push with your foot. The CC module actually "pulls" on the accelerator pedal in order to maintain cruise control :

Attachment 707

CarloSW2

Hahaha... well that explains how the CCM gets to control the speed! :p I was so into the schematic aspect I was thinking completely "drive-by-wire" (versus "drive-by-cable," I guess. :D)

Could very well be... in which case my guess for "MOVE" is likely bogus too.

CarloSW2, is there no "theory of operation" stuff in that repair manual at all?

Rick

skewbe -

Unless I misunderstand your statement, I think Rick's description makes more sense. When you say "trying to adjust your speed", that makes me think that the CC Module has more smarts in it than it actually does. I think the module just controls a motor that pulls the CC adjuster cable. The brake and clutch are fail-safe inputs to turn it off.

But, the best thing to do is attach a multimeter and see what happens. I keep thinking that this is a job for an oscilliscope or a "voltage logger" (which I guess is another word for oscilliscope).

CarloSW2

Rick -

The Haynes manual doesn't have much, I only used it for the electrical diagram.

I keep scavenging these el-cheapo Saturn CD manuals from ebay for $10 and $15 bucks because I don't want to fork out $200 for a real Saturn shop manual (I just ordered my third el-cheapo today) . Once I get the CD, I putz around on it until I find something useful.

I never knew the CC module even existed until a week ago, even though it was in the electrical diagram the whole time.

I think that the right thing to do would be to open the CC module up. However, I also know the replacement cost to be around $300 retail!!!! If I were smart, I would go to a pick-a-part and see if I can buy one for autopsy. But maybe that would cost a chunk of change too. Hrmmmmm, I guess I wouldn't actually have to buy it. I could take it out and dismantle it in the junk yard, take pictures, put it back together, and leave it for someone else to buy.

CarloSW2

Hey Carlo, If you do scope it, can you tell me what the blue line looks like when cruise is working and what it looks like when the clutch is pressed in? I tried a couple simple things to no avail.

skewbe -

OK. It will take me some time. I like to build harnesses for this stuff, so I will try to match the 6 line connector. I could tap into the existing wires, but I like to leave original wiring pristine where possible.

CarloSW2