Dear Jim,

I have a 1996 Cadillac Eldorado (4.6 L, V8, 62,000 miles) and something is wrong with the charging system. The voltage gauge on the dash reads 12.2 volts, which I've been told is too low. I've had two brand-new alternators installed over the last several weeks to fix this. When the mechanic checked the voltage at the battery, it was 13.4 volts, which is good. He said the gauge was probably wrong, so I took the car to the Cadillac dealer. They ended up replacing it, plus something called the BCM and the power supply computer, but the new gauge still reads 12.2 volts. What's going on here? I want this gauge to be accurate, so I'll know if there's a serious problem.

-- Renee Lunsford

Understood, sister. From what you're saying, I'm guessing the charging system is probably working just fine, but you do need to be able to trust your gauges. So then, you took your Eldorado to the Cadillac dealer and they replaced the voltage gauge, the body control module (BCM) and the power supply computer.

At first, that sounds like a thorough (not to mention highly expensive) fix for this problem, but it turns out to be a bad one in this case.

Dealers are funny, see. You'd think they would know their own vehicles better than anyone else, but that's not necessarily true. The employees who are actually replacing these parts often know less about the car than an independent mechanic would. The result here is that you got charged a lot of money for a new BCM, etc., because someone didn't know a crucial piece of information: The voltage gauge on a 1996 Cadillac Eldorado runs through the engine control module (ECM), not the BCM.

If this digital gauge is getting the wrong information from some computer system, it's going to be the ECM that's at fault. Not all service stations can install and program new ECMs, but Carquest Auto Parts (3341 Industrial Road, Las Vegas, 702-735-2062) is one that can. Ask for either Bobby or Duncan. Once that new unit is installed, you should see the dashboard voltage gauge finally agreeing with what the battery is saying.

Tip of the Week

Sluggish shifting in your automatic transmission? Consider picking up a can of transmission conditioner for around $7 at your local parts store. It won't make things good as new, but it may buy you another few thousand miles before that old transmission really needs replacing.

Buffalo Jim, owner of Allstate Auto & Marine Repair in Las Vegas, writes a weekly column. Send your automotive questions to him at buffalojim@lasvegasniftynickel.com. If Jim picks your question to answer in Nuts & Bolts, you'll also be the proud recipient of a deck of official Buffalo Jim playing cards, presented in a classy, tin box bearing his hairy image.