I am extremely frustrated with the engineers insane need to over-complicate their cars by adding a bunch of unnecessary, unreliable computers. It's why I still drive a 1988 Grand Caravan and will never own anything newer than my '89 Voyager. Ok, I have a '93 Dynasty with a bunch of computers, but I've only driven it 4,000 miles in 16 years so I obviously don't have to rely on it.
Yes, your battery could be contributing to the problem. Computers are very sensitive to supply voltage. A fully charged battery will measure around 12.6 volts. It is acceptable for that to drop to as little as 9.6 volts during cranking. Engine oil gets thick and gooey when it's cold so the engine cranks harder. That requires more current and further draws the battery voltage down.
The battery is a chemical reaction. Chemical reactions slow down as the temperature goes down, so now you have a battery that is less capable of providing the necessary current AND the cold engine makes the starter demand more current. Both of these cause the voltage to drop. Even though the starter may still crank the engine, the point may have been reached where the voltage is too low to run the computers.
To share an example that took years to figure out, a weak battery caused a no-start condition on my van even though I thought it was cranking just fine. There was an initial bog to the starter during which time the battery voltage was drawn down so far, the engine computer stopped firing the ignition coil and spark plugs, but it DID still fire the injectors. The system didn't reset and fire the spark plugs unless the ignition switch was turned off first, then turned back on and cranked.
I only have an engine computer which has been extremely reliable. In your case, you have possibly a dozen or more computers. They all talk back and forth to each other on a pair of wires called the data buss. The voltage for the data buss is generated in the body computer. It's purpose is to run the power windows, power locks, and interior lights, (all things I have that run with simple, reliable switches), but it also is involved with the remote keyless entry system and anti-theft system. If low battery voltage shuts the body computer down, the data buss will be dead and the other modules will be affected since they can't receive information from each other. The engine computer could also do strange things due to low voltage. My experience has been that engine computers will not lock up to the point you must disconnect the battery. A simple jump start or cycling the ignition switch off and back on will get it going. Body computers are another issue. They do some of their functions when the ignition switch is off, (interior lights and headlamp-on chime are examples), so they stay powered up unlike other computers that turn off when the switch is off. That's why on newer cars you must disconnect the battery for a minute or two to reset them.
Wednesday, December 16th, 2009 AT 9:20 AM