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Cruise Control 2.5 Boxster


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I read a couple of similar, unresolved threads that describe the problem that I'm having:

Green indicator lamp lights but I cannot set cruise. I know it worked in early June.

1 - in early July, the clutch/starter interlock switch started to require two or three pushes before the car would start. I jumpered the switch. This shouldn't make a difference.

2- I cleaned and checked the other clutch plunger switch - it seems to be operating well.

3 - I've done work in the engine compartment and replaced the battery this summer. Are there any vacuum or electric connections that I could have disrupted?

Any ideas before I give up and call the dealer?

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I vaguely remember something about cruise control not working if a brake or tail light is burned out. I'm in a hotel room on the east coast this week, so not easy to track down, but it was probably on one of the main Porsche boards you would expect (here, PPBB, Rennlist, Rennteam, etc.)

Have you checked all your light bulbs to make sure they work?

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I've had a look at the PET and wiring diagrams for cruise as it is one of my fantasies to retrofit it to mine (fantasy as currently no parts, ability or motivation). There is some info I posted on a Boxa.net thread here:

http://www.boxa.net/forum/index.php?showtopic=12789&hl=

I don't think that a faulty brake light would stop the cruise working, but the unit is supplied with power from the stop light switch, so if this fuse has blown (caused by the stop light blowing, maybe?) then that might cause the problem. Fuse is B7, 15A. Second row down seven to the right. Might be worth changing if the brake light is not working.

There is a clutch switch input to the cruise control. What do you mean by 'jumpering' yours? The wire from the clutch switch goes to the cruise control unit and then on to the tiptronic something or other.

Finally, for my own education (never seen a car with cruise) where is the green light you refer to. On the dash I presume?

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I've had a look at the PET and wiring diagrams for cruise as it is one of my fantasies to retrofit it to mine (fantasy as currently no parts, ability or motivation). There is some info I posted on a Boxa.net thread here:

http://www.boxa.net/forum/index.php?showtopic=12789&hl=

There is a clutch switch input to the cruise control. What do you mean by 'jumpering' yours? The wire from the clutch switch goes to the cruise control unit and then on to the tiptronic something or other.

Finally, for my own education (never seen a car with cruise) where is the green light you refer to. On the dash I presume?

Thank you for all the info - Fuse was good - all the lights are working (C.C. lamp in the lower right quadrant of the speedometer).

'jumpering' - there is a microswitch on U.S. cars that functions as an interlock between the clutch and ignition. If the clutch is NOT depressed, the car won't start.

This switch was specified by the lawyers - not the engineers. They tend to wear out or get 'gummed-up'. When they do, the engine will not turn over until the switch makes eventual contact. As a work-around, I installed a short wire (jumper) between the two sides of the switch until I could replace the switch.

I revisted my work and discovered something that I had overlooked. The main clutch switch has a plunger - when I was working on the microswitch, I apparently pushed the plunger in which didn't allow the switch to function properly. I reset the plunger and all is now good.

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Here's how I resolved the issue. It's generally helpful info regarding Cruise Control issues. The car is a non-egas 1999 with 54k miles. Both Clutch switches had a considerable build-up of crud inside them so I removed, cleaned and reinstalled the switches. There is a plunger on the main clutch switch that needs to be reset after reinstalling the switch - that was the primary cause of the cruise control failure. Here's what I did in some detail:

1 - removed microswitch (small rectangular)clutch/ignition interlock

cleaned it with Caig's Gold. Blew it out w/air

2 - replaced said switch - still no CC.

3 - removed plunger switch (this is the one that communicates with ECU directly affecting Cruise Control). Took switch apart, cleaned it. It was full of grease etc. The grease may be a necessary part but, it didn't look good so, I cleaned it w/Caig's and applied compressed air, reassembled and replaced - still no CC.

4 - Here's what finally did the trick:

depressed the clutch pedal and observed the switch action. I pulled the plunger all the way out of the switch til it stopped (it has a kind of ratchet effect). Released clutch pedal (the most difficult part of this operation is depressing and releasing the clutch while lying on one's back underneath the dash).

Voila! Cruise Control now works.

A lot of effort for something that I rarely use

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Glad you got it sorted. Am I right in thinking that the clutch plunger switch had gone too far down and you had to pull it back up to get the cc to work? What happens the next time you depress the clutch -- won't the plunger remain too far depressed?

Don't suppose you could take any photos of the item concerned so I can see what it looks like? (It's either picking up info like this or buying a car with cc and dismantling it to see how it is all put together :) )

Edited by Paul Fraser
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Glad you got it sorted. Am I right in thinking that the clutch plunger switch had gone too far down and you had to pull it back up to get the cc to work? What happens the next time you depress the clutch -- won't the plunger remain too far depressed?

Don't suppose you could take any photos of the item concerned so I can see what it looks like? (It's either picking up info like this or buying a car with cc and dismantling it to see how it is all put together :) )

You are correct - the 'ratchet' action is auto correcting.

I'll try to take a photo. It's not the easiest place to negotiate so, don't hold your breath!

Funny you mention it, I was thinking today that I should have documented the procedure w/photos.

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