Cruise control not working, where to start???

[CJP5]

The last item on my '88 911 that's not working is the cruise control. Looking for someone who can suggest, in order from easiest to hardest, where to start checking.

[Hendog]

Reflow all the suspicious solder connections on the PC board of your cruise control module. That's what I did and it worked thereafter. Now, I'm an electronics tech and work with a soldering iron, so my apologies for sounding so flippant about the ease of effort.

The module is found underneath the dash. It's a silver box like this:

Remove the module, pull the plastic cover off, pull out the PC board and resolder a bunch of connections, mostly around the IC's and devices with heat sinks.

You should put your location in your profile, it helps others determine if you're within help-range.

[llangston1]

Check the electric circuits and contacts at the brake disconnect switch and the steering column control. Then you could check the vacuum lines to the engine bay controller.

[DRACO A5OG]

+1 Check Vacuum in connected to the SERVO in the engine bay. There are two hoses on top of the SERVO (BARREL). One facing you is the thicker breather hose. Right behind it is the vacuum line, make sure it is connected, and tight. then follow it down to insure the Y connector is snug as well. If all good check out the ECU as stated above.

[CJP5]

Originally Posted by llangston1

Check the electric circuits and contacts at the brake disconnect switch and the steering column control. Then you could check the vacuum lines to the engine bay controller.

Pic of the engine bay controller? Where in the engine bay is it located?

Thanks!

[DRACO A5OG]

It is that cylinder thing with the cable coming out the center of it and connected to the Throttle Arm.

Driver side

[CJP5]

Hey, it's my first Porsche and I've only had it for 6 weeks. Appreciate the help.

[megerian]

My '88 also has a non-working Cruise Control. I thought it was the clutch switch, now I figure the main module is the culprit, but its not at the top of my to-do list yet. Also, on my '88 the servo is electric, not vacuum, so no hoses. This was discussed a few months ago.

The Bentley manual has a fairly extensive troubleshooting guide.

[preston_brown]

Had my module on my '87 reconditioned locally...it slowly bled off speed when active. Has worked perfectly form the 7 years since.

[DRACO A5OG]

Originally Posted by megerian

My '88 also has a non-working Cruise Control. I thought it was the clutch switch, now I figure the main module is the culprit, but its not at the top of my to-do list yet. Also, on my '88 the servo is electric, not vacuum, so no hoses. This was discussed a few months ago.

The Bentley manual has a fairly extensive troubleshooting guide.

Ooops my Bad!

No worries CJP5, we are here to help! Sorry about the bad post, I can't get my old mind out of the 84-86 3.2

[CJP5]

If anyone has pics of the brake clutch disconnect switch post them please. Where is the switch on the car exactly?

[megerian]

Here is a thread talking about the clutch switch:

Clutch Switch for Cruise Control

[wwest]

Originally Posted by CJP5

The last item on my '88 911 that's not working is the cruise control. Looking for someone who can suggest, in order from easiest to hardest, where to start checking.

Brakes lights ALL working and OEM incandescents NOT LED....??

[Brorag]

try cleaning the pins of the cruise control relay in the engine compartment--fixed mine......................

[porschenut]

Rather than taking an inefficient, shotgun approach to this, I suggest a more logical approach. Help us to help you:

1. First of all, provide more details about what EXACTLY happens when you try to engage the CC. "not working" is not very helpful. Does it engage and then slowly lose speed? Or does "not working" mean absolutely nothing happens when you hit the switch?

2. You asked for people to list easiest to hardest. None of the respondents has yet bothered to do that. Easiest is to check the fuse in the luggage compartment. Next easiest is to check the relay by replacing it with a known good one. Next easiest is to use a digital multimeter on the ECU connector and the troubleshooting guide in the Bentley manual. If you don't have a Bentley manual or a digital multimeter, they should be at the very top of your shopping list.

After you've checked the fuse, the relay and gone through the Bentley troubleshooting procedure, in that order, come back and give us your results. THEN we can help you further.

[dshepp806]

Originally Posted by porschenut

Rather than taking an inefficient, shotgun approach to this, I suggest a more logical approach. Help us to help you:

1. First of all, provide more details about what EXACTLY happens when you try to engage the CC. "not working" is not very helpful. Does it engage and then slowly lose speed? Or does "not working" mean absolutely nothing happens when you hit the switch?

2. You asked for people to list easiest to hardest. None of the respondents has yet bothered to do that. Easiest is to check the fuse in the luggage compartment. Next easiest is to check the relay by replacing it with a known good one. Next easiest is to use a digital multimeter on the ECU connector and the troubleshooting guide in the Bentley manual. If you don't have a Bentley manual or a digital multimeter, they should be at the very top of your shopping list.

After you've checked the fuse, the relay and gone through the Bentley troubleshooting procedure, in that order, come back and give us your results. THEN we can help you further.

BIG +1!!!!!!!!


Doyle

[CJP5]

Originally Posted by porschenut

Rather than taking an inefficient, shotgun approach to this, I suggest a more logical approach. Help us to help you:

1. First of all, provide more details about what EXACTLY happens when you try to engage the CC. "not working" is not very helpful. Does it engage and then slowly lose speed? Or does "not working" mean absolutely nothing happens when you hit the switch?

2. You asked for people to list easiest to hardest. None of the respondents has yet bothered to do that. Easiest is to check the fuse in the luggage compartment. Next easiest is to check the relay by replacing it with a known good one. Next easiest is to use a digital multimeter on the ECU connector and the troubleshooting guide in the Bentley manual. If you don't have a Bentley manual or a digital multimeter, they should be at the very top of your shopping list.

After you've checked the fuse, the relay and gone through the Bentley troubleshooting procedure, in that order, come back and give us your results. THEN we can help you further.

Great answer to my question and I appreciate the list. To answer your question, nothing happens when I engage the lever. The fuse is good, not sure about the relay. More to follow...

[Por_sha911]

After the fuse, make sure the cable connected from the servo to the throttle is not broken. Next, find someone with a working cruise and swap out the brain to see if its bad. IIRC, 2 bolts per car.

[CJP5]

Fuse is good, new brain, cable from servo to throttle body is connected... Off to buy a new relay tomorrow. And yes, I've ordered the Bentley manual, but it's not here yet.

[CJP5]

The cruise does not engage at all. I've replaced the relay, checked the fuse...it's good, replaced the module.

Yesterday I received the Bentley manual and I went and bought a multi-meter. Couple of questions...

1. Bentley manual pg 960-12 lists the CC trouble shooting table and steps. Do you know if terminal 1 in the control module harness connector is the ground? Trying to make sure I'm testing correctly.

2. Are the Clutch pedal switch and the Brake light switch the same switch, are they two sep switches and are the both located in the "tunnel" under the center console? I had the pedals exposed and I do not see either of these switches. Based on my testing, if I'm doing it correctly, both these switches are faulty.

Thanks,

Chris