Lil4X

Running to the store yesterday, my wife called me to say the instrument cluster in our ancient grocery-getter died. The van ran fine, all other electrics were operating normally, but all of the gauges fell to the "0" peg . . . and stayed there.

First thought was a fuse. Seems the instruments are all routed through a common fuse . . . but it was fine. Then I recalled a similar problem with an "interrupter" on our Dodge-chassis motorhome, and went online to chase down my hunch.

Well, long story short, it seems the "interrupter" that multiplexed the gauge signals over common wires went the way of the dinosaur some time ago, to be replaced by the Body Control Module, or BCM - a rather simple computer that controls the instruments in practically all cars built since the late '80's. To their credit, most of these little processors usually soldier on for decades without complaint, but they have been known to crash. That's what ours did . . . that little warning light that appeared in the cluster said "check gauges" - sort of the pre-Windows BSOD.

It turns out that over the years the BCM has gotten much more complex, handling all of the body electronics (except the radio and nav modules), including the door locks, windows, instruments, and a dozen other electronic controls and displays. Soon after Daimler Benz bought Chrysler (1998-2007), they began sharing engineering and some components - and Daimler's complex BCM was incorporated into Chrysler's products where it became a nightmare to some Mopar owners.

Several other manufacturers are having similar problems today - ones that don't often appear until the vehicle is several years old, but they can be mind-boggling because they just don't fit conventional expectations for automotive troubleshooting. Here's the deal: It's also a computer, and like any computer, it can develop a hiccup and crash. After tens of thousands of operational cycles, ours quit. After a good bit of online sleuthing, I found the answer.

The solution is embarrassingly simple: reboot. If you have experienced mysterious failures in any of your instruments or accessories, disconnect the ground cable from your battery, and walk away for a cup of coffee. When you return and reconnect the battery, you may find that after an operational cycle (ignition on, start, run, ignition off) or two, everything has returned to normal. Once the BCM has rebooted and shed itself of its internal gremlins, all should be well, with instruments properly reporting to the bridge.

For anyone maintaining a vehicle with more electrical accessories than a lawn mower, computers are now a big part of their design - and need to be considered in your mental checklist when troubleshooting.

mmarshall

Did you find that you had to reset all of the radio-station buttons, clock, trip odometer, (if electronic), etc.... and put up with erratic engine-idling while the engine-computer reset itself? These are common conditions that happen (or can happen) when you disconnect and re-connct a battery cable.

Lil4X

Oh yes, the radio presets cratered big time, but the primitive fuel injection staggered to life without missing a beat. I have a suggestion for manufacturers of electronic devices of all kinds: put a capacitor or even a small rechargeable battery in the device simply to maintain memory for a few minutes. Programming a couple dozen radio stations and resetting the clock is a pain, but I'm getting enough practice at it, that it doesn't take me long.

Chrysler Corp claims to have a solution for all this: that you unplug the BCM. Unfortunately locating it above the driver's left kneecap behind the dash, it is inaccessible to all but well-trained rhesus monkeys. The service manuals actually recommend you disconnect the BCM for long-term storage of the vehicle, so I assume it requires some minimal amount of power to maintain its memory.