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Voted most useless member
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Discussion Starter · #1 ·
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It looks like this:

This unit is only on the 1996-2000 Minivans.

More on this Unit can be found here at ALLPAR

The most important this about this unit, is that it also is on something called the CCD bus. In our 3rd Generation vans, its a serial data bus of sorts. Kind of like USB for your car. But unlike USB, if you unplug something? The whole thing goes down. So its kind of like a Token Ring Network. In that style of network, if something is broken, the token can not pass to the next computer. So any breaks in the system, bring the whole network down.

Image Stolen courtesy of Google. Blame google.....

Your HVAC computer is part of this network. This Network includes:

  1. Body control Module or BCM.
  2. Engine Management Computer or ECM.
  3. HVAC control module computer. (also your wipers or rear wipers)
  4. Transmission control module. or TCM.
  5. The Instrument cluster Fu.....
  6. And others.

Any one of these computers go out , you might see these problems:

  1. You can't start your car. It may crank, but not start.
  2. loss of wiper controls
  3. wipers behaving intermerintly.
  4. HVAC not working properly or cold or hot but never what you want or erratic behavior.
  5. Lights not working or not alarm issues.
  6. Door lock issues.
  7. Your radio may not work anymore.
  8. your instrument cluster will not work right, or conks out, or does weird stuff.
  9. Your alarm my just go off for no reason.
  10. your doors may lock or open by themselves.
  11. your car may stall.
  12. YOUR REAR WIPERS MAY NOT WORK Or, as user, said, may turn on with the car without pressing the button.
  13. weird chimes.
  14. OBD codes you have no idea what they are for.
  15. Defrost may not work.
  16. Auto dimming may not work (not sure if part of the bus)
  17. lights may not turn on in cabin, or turn on randomly.
  18. headlights may even stop working.
  19. door locks may not function.

Most people go out to replace the BCM. As a good Buddy says: JUST DON'T.

Image stolen Courtesy of Giffy

The real problem centers are bad connections in the car. This can be from Burnt grounds, broken solder joints.

The Threads on this are here on this forum.

A photo of what the HVAC connector looks like:

See that burnt Pin? That the ground pin.

This thread also shows how the solder joints can break and how to fix it. WAY back in 2007! Also with PHOTOS!

Images Courtesy of maxwell1295

As he link from Allpar stated, this is apart of the CCD bus. Newer cars use Canbus. Its like FIrewire IEEE-1394 data bus, but for cars as we talked about above in the link. But unlike firewire, we have an older data bus of dumb computers. If one thing goes down, they all go down.
You can connect to this data bus and read it, but you need special tools. A basic OBDII reader and software package will not do it.

So now you have to find what the problem are the old fashion way. That means looking and pulling items to see what is wrong. Its a pain, but it must be done. And as are Vans are over 20 years old now? Its going to need some TLC at this point.

Any one of these computers can go wrong. But these are the most common.

  1. The Instrument cluster data Solder joints and pins.
  2. The HVAC unit connector, and ground pins.
This is due to Mechanical stress, or heavy current loads. Oxidation of the pins can occur, The pins from the factory are plated for the most part. But during high current demands, the coating can burn off leaving the exposed copper. Overtime, this will cause higher heat, and therefore, either break, burn, or simply cause some kind of failure that will knock out one of these computers in the token ring data bus that the computers all connect to . Essentially causing a system crash or malfunction that takes out the Van, or causes intermittent failures or odd behavior of the electrons in the van.

Before you go and replace your BCM, THIS should be the first things you should do before you start replacing an expensive item such as a BCM. ECM, TCM, etc.

Before just replacing the unit, repair is possible and easy to do with just simple tools you can steal from Shipo's house. He has lots of soldering Irons. Take one. :)
He won't mind. I promise! * You can also just buy these things on Amazon or at the forum sponsors. You can also just send your items to Louis Rossman of the Rosman group who will be happy not to do the soldering work for you want a pro to take a look at it that soldiers stuff like boards for a living..

* May lead to loss of life and limb or Ban from the forums, or Jail time or FUneral costs. Not recommend.

Once you tackle these repairs, and verify that these items work, you can reinstall them, and most of the time, everything will go back to working again.

You may need to recalibrate your HVAC unit. Here is a video showing you how.

The moment you have ALL been waiting for.

In this video, I show you how to see if your Flaps, and motors are still working. You will need headphones or some good speakers to hear them.
I did this on New Years day, at 3PM And as the Joke goes, I only work after dark. Much like the screen saver or a prostitute. Its nice and quiet, so you should be able to hear what the motors sounds like.

In the VIdeo, I am putting the car in the ACC position. The Vans Engine is not started. The fan is not blowing. But the motors and solenoids & actuators are all moving or making noises. This does not mean the FLAPS are moving. They can be broken. Its just plastic. It should sound different from what you hear in this video.

As always, say the MINIVAN Prayer before you start any work on your van.
And that is the MOST serious post I have ever made on this website this year. But we just started. So... :)

67 Posts
Thanks for this. I'm gonna check my HVAC connector before I try changing my BCM. My problems all seemed to start with the rear wiper going crazy.
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