Cruise control fix
Thread Starter
Drifting
Joined: Jul 2014
Posts: 1,426
Likes: 46
From: Lynchburg, VA
Cruise control fix
My 1990 has never had working cruise control. Some recent projects gave me the opportunity to get familiar with the electrical portion of the FSM, so I finally decided to grow a pair and work through the FSM diagnostic procedure for the cruise control. Sadly, one of the first steps required accessing the cruise control module, which is up in the passenger side of the dash. The radio receiver is underneath it, so you have to pull off the kick panel (which requires removal of the fuse panel), remove the radio receiver, and then remove the cruise control module. Sounds easy on paper, but things are packaged so tightly that it's a real bear. And of course being upside down underneath the C4's dash is no picnic.
I ran a bunch of tests on that, and the conclusion was unfortunately that there was a break in the cruise control enable circuit. After staring at the circuit diagram for awhile, I noticed that there are two switches in series in this circuit. An automatic car would have just the brake pedal switch, but the manual also has the clutch switch. Sure enough, the clutch switch was bad. I found a replacement for $20 online, but I noticed that the switch housing could be taken apart. I did so, and the guts are about as simple as you could possibly imagine. I suppose that's probably the norm for a mechanical switch like this. I cleaned up all the contacts with some maroon Scotch-Brite (emery cloth would probably be better if you have it), smeared on a little dielectric grease (important to prevent corrosion), and slapped it back together. Worked like a charm!
I reinstalled the switch, and cruise control still didn't work. Turns out the brake pedal switch was also bad! Same deal: tore it apart, cleaned the contacts, greased it, and threw it back together. Once I realized I had forgotten to reconnect one of the vacuum lines (whoops), cruise control worked like a charm!
I'd guess these switches are a common failure point, so I thought I'd share my experience to hopefully save some people some trouble. It's free and relatively easy, so I'd definitely recommend checking these switches out before you go to the trouble of pulling out the cruise control module.
I ran a bunch of tests on that, and the conclusion was unfortunately that there was a break in the cruise control enable circuit. After staring at the circuit diagram for awhile, I noticed that there are two switches in series in this circuit. An automatic car would have just the brake pedal switch, but the manual also has the clutch switch. Sure enough, the clutch switch was bad. I found a replacement for $20 online, but I noticed that the switch housing could be taken apart. I did so, and the guts are about as simple as you could possibly imagine. I suppose that's probably the norm for a mechanical switch like this. I cleaned up all the contacts with some maroon Scotch-Brite (emery cloth would probably be better if you have it), smeared on a little dielectric grease (important to prevent corrosion), and slapped it back together. Worked like a charm!
I reinstalled the switch, and cruise control still didn't work. Turns out the brake pedal switch was also bad! Same deal: tore it apart, cleaned the contacts, greased it, and threw it back together. Once I realized I had forgotten to reconnect one of the vacuum lines (whoops), cruise control worked like a charm!
I'd guess these switches are a common failure point, so I thought I'd share my experience to hopefully save some people some trouble. It's free and relatively easy, so I'd definitely recommend checking these switches out before you go to the trouble of pulling out the cruise control module.
