BODY CONTROL MODULE
March 27, 2011
In addition to the transmission issues that Dodge Caravans are known to have, having the instrument cluster go out is another common problem which I had the luck of experiencing. And similar to the transmission problem not actually being a transmission issue, the problem with the instrument cluster has nothing to do with the instrument cluster.
On the Dodge Caravans (and many other Dodge vehicles, apparently), the Body Control Module (BCM) controls several functions of the minivan:
• Automatic door locks
• Battery protection
• Compass/mini-trip support
• Courtesy lamps
• BCM diagnostic support
• Door lock inhibit
• Headlamp time delay
• Ignition key lamp
• Illuminated entry
• Instrument panel dimming
• Mechanical instrument cluster support
• Power door locks (with/without remote keyless entry)
• Sliding door memory lock
• Vehicle Theft Security system (VTSS)
• Windshield wipers / washers (front and rear)
I read through as many forums as I could to see if I could trace down the root of the problem. If I could avoid buying an expensive part for the van, that would be ideal.
The first thought that was that I'd have to replace the BCM outright, which I could pick up for about $100 on eBay. However, the problems with the instrument cluster not showing anything was intermittent. Sometimes, I could tap on the cluster and it would kick back on. That didn't sound like a computer issue. It sounded more like a loose wire, so I pulled the BCM plugs and checked everything to make sure that there wasn't anything amiss. After that, I pulled the instrument cluster to see if anything seemed loose back there, but I couldn't identify any problem.
After a little while of dealing with the intermittent gauge cluster problem, I noticed that there was also a problem with the heating/AC controls. I could turn the air on and off, but the temperature and direction (face, floor, defrost, etc.) was stuck on defrost. This didn't seem like it was related to the BCM, but the problems started at the same time, so I decided to see if I could find a common ground between the two that could be causing the problem. I was going at this blind, because the wiring diagram in my manual didn't show any common grounds.
Pulling the heater control panel was a matter of removing four screws: two shown above the CD player, and two down below, under a cover above the cup holder.
There are three plugs to deal with. The plug with the 21 pins turned out to be interesting.
Unfortunately, my wiring diagram pin-out only explain what pins 1 through 19 control.
It's hard to see in this photo, but the bottom-right pin was brown, in contrast to the other shiny silver-colored pins. I didn't think much of it, but then I looked at the plug itself.
Yup. The spot that held pin #21 is melted. There is a loose connection at that location, and the repeated arcing heated up the plug and ended up coating the pin, severing the connection entirely. After a couple of minutes of scrubbing the pin and tightening up the plug, I put it back together and my instrument panel worked perfectly.
Weird, right? Why would a break at the heater control have anything to do with the instrument cluster, via the BCM? Wiring efficiency, I guess. Having common grounds across different circuits saves on wires, but it sure make it seems like there are gremlins in the system. On the other hand, it did make it a little easier to trace down the bad ground, because I went into it assuming that the problems were related. The forums I've read on this problem have never linked the gauge cluster and the heater controls. In fact, the responses I read to someone else with the exact problem stated to view the two systems separately, and to start with replacing the BCM. In this case, that wouldn't have helped.