Go with the ReFlow – Bake Your Broken Cruise Control Computer


For years my Saabs all had inoperative cruise control. I would collect cruise computers from every c900 in the junkyard and stockpile them. If I found a working one, I would cherish it, knowing that mine was among the rarest of the rare… a Saab c900 with working cruise control.

One day a friend suggested I try repairing it by heating up the cruise control computer to soften the solder joints. He said IT guys do it all the time. I asked my IT guy at work and he confirmed that it was called “Reflowing” and was typically used on computer motherboards that were on the fritz. Solder tends to degrade over time, developing cracks and pores that decrease the signals that can pass through them, although these fractures are typically too small to be seen. They would bake them in the oven for a short time to soften the solders to refill the cracks and pores and make them solid again.  If the cracks are really bad, a paste of powdered solder and flux can be applied to help with the process.

http://i.imgur.com/dW6DDJt.jpg

I had my stockpile of broken cruise computers with no future except as an art project, so what did I have to lose? Here’s what worked for me.

First, be sure that you have correctly isolated the problem to the cruise control computer. Check and replace any bad vacuum lines or switches, and test your system with a known working cruise control computer if possible (check the parts list for your car on eEuroparts.com). This procedure should be considered a last resort for computers that are known to be inoperative.

http://i.imgur.com/QhUQxmC.jpg

1. Start by removing the plastic end plate(or the entire plastic outer cover if it’s a relay) to expose the inner motherboard

2. Soldering alloys have a melting point of around 360°F, but a lower temperature always has worked for me. Preheat the oven to 300°F

3. Set the unit on a piece of tin foil on a something less-conductive like a ceramic oven-safe plate and let it bake for exactly 8 minutes

4. After 8 minutes at 300°F, turn off the oven and let it cool down for about 10 minutes – so that the transition from hot to cold did not cause it to re-fracture

5. Once cool, take it out of the oven, put it back together, and plug it into the car to try it out

 

http://i.imgur.com/gjMUjWp.jpg

The first time that I tried this, the cruise control worked intermittently for the first run. But the next drive, it engaged and held. It’s been a year and a half now, and it’s still working perfectly. I ended up baking every one of my cruise computers and handing them out to my good friends like Hershey bars. No more stock pile!

This process has also worked for me on other small automotive computers and relays – central locking modules, ECUs, APCs, relays (especially the always broken Saab 9000 headlight relay). Just remove any removable plastic, bake at 300°F for 8 minutes and cool down. So if nothing else works, put on your apron and start baking!

http://i.imgur.com/VlnrS2Q.jpg
* Disclaimer: *
This article is meant to be purely informational. eEuroparts is not responsible for any damage, either direct or consequential, to your auto parts, to your oven or to any person or property as a result of attempting this procedure.

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Posted in DIY How-To, Saab
9 thoughts on “Go with the ReFlow – Bake Your Broken Cruise Control Computer
  1. Great tip! We used to back-date the cruise ecms to the earlier style ecm & plug, which never seemed to fail, but this is even easier! We’ve been doing this with a variety of relays and control boards, for awhile, now, so why not!

  2. dan

    Surprised that works.. even at all.
    Cooking the entire Unit…. Plastics and all.. Really !??
    When just the touch of a Soldering iron tip to the visibly damaged connection would do the job.. securely and elegantly.. in seconds.
    But then one would have to open the can… bend back the ali tabs a bit. Too hard ?

    • Don’t forget to check out step 1 – remove any removable plastic. That said, there isn’t much left once you remove the end-plate on the c900 CC computer. You’re right, though, the melting point of plastic is lower than that of solder, but I have never had any problem with melting any plastic. Could be that it’s such a short time that it’s in there. The tabs on the CC computer are easy to pull back with a flat head screwdriver. Plastic relay housings are a bit harder and seem to take three hands, but definitely not impossible for a normal DIYer like you and me. Good luck!

  3. I have not tried this process yet so I may be talking out my ass, but solder reaches its liquid state at 690 to 750 degrees F, well above the melting point of any plastic on the pcb. I know a guy that claims to have repaired the ecu from a 98 civic that I had diagnosed as defective. However, he has misplaced the keys, so I am unable to verify that it works

    • Sam Williamson

      I’m still pleasantly surprised that this works almost every time. I’ve done it both ways – soldering works great as well, it just takes longer. I usually solder when the cracks are clearly visible or little pieces of solder are missing.

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