bent valves

The battery temperature sensor is needed not only to prevent an overcharged battery but also to insure a 100% charge at all temperatures. It turns out that a charging system that stays at one voltage, like 13.8 volts will overcharge the battery when the temperature is hot and this will shorten battery life. Also when the temperature gets cold a fixed voltage charging system will not fully charge the batteries.

Dodge is no dummy when it comes to saving a buck. The added expense of a temperature compensated charging system allows them to use a smaller battery for cold weather starting. This is because the battery is fully charged at a higher voltage from the last time the truck was run. In Hot weather where an overcharged battery will quickly boil out the acid, the temperature compensation allows the truck to get through the warrantee period. (I guess I’m just cynical.)

Here is a chart showing how the battery voltage relates to battery temperature. If the voltage is at the indicated level in the chart, the battery is at 100% charge. The charging system must be a volt or two higher than the battery to force a charge.

vzdude

Very good info Dave. I think that helps make sense of it all a little better.

fozzy777

In advance I will apologize for reviving this old thread. Smokeyram did you ever check your voltage with a voltmeter? I have had an overcharging problem for about 1.5 years. My truck charges @ 14.7 to 15.4 at any given time. I have never heard that the temp sensor controls charging. This is interesting because i have thrown that code since the first year I've had my truck. When I asked the dealer about it he said " it's normal ". I'm on my third set of batteries and I go through headlights every six months. I have talked to every mech. at my dealership and they all say since the ECM controls alt output I need a new one or the ground cable from the ECM to alt is faulty. I checked the later and it seems fine. I'm going to try changing the temp sensor and see if that helps. If you are having a charging problem, I will contact you on my results.

bent valves

Fozzy777, I’ll take a shot at your problem. If you are seeing a code for the battery temp sensor it could very well cause the batteries to overcharge and fail. In the second-generation trucks a P1492 code will come on if the temp sensor becomes disconnected. This will fool the PCM into thinking the batteries are cold and increase the voltage. It will also set the check engine light. I don’t know if it is the same for a third-generation truck but it probably is. One likely cause is if the temp sensor becomes disconnected or intermittent. The code is not “normal” and shows there is a fault with the charging circuit.

smokeyram

i didnt actually put a meter on it. we got an obscene warm up last week, so i dealt with a host of other things. i will have to now that the temp is dropping again. speaking of codes, on my 96 dont i need a reader to check?
the only digital thing on my hunk is the aftermarket radio.

WestTN

The required voltage to properly charge a lead-acid battery varies with temperature. It is chemical reaction that produces the voltage and all chemical reactions are temperature dependent. Sorry, no conspiracies here.

SIXSLUG

Is the battery temp sensor that effective? Why is it mounted under the battery? It would seem to me it would be better located on the side or actually in the battery. Replies? Kurt