MY 2000 5.4 had its battery light come on this morning. It is also idling(in park and drive) higher than normal. The lights seem to be dim also.

Any sugggestions?

 

Could it be the alternator????

 

How old is the battery? I would have it checked if it is fairly new, and have the altenator checked. If the battery is over 3 years old, I would just change it and maybe still have the altenator checked.

 

i just got a new battery about a month ago. I havent changed the alternator since i had it(about 4 yrs). i was gonna have it checked but nothing's open yet here.

 

Do you have a voltmeter? Voltage at the battery terminals with the engine at idle should be somewhere in the 13.9-14.1 V range with the lights off if the charging system is OK.

I don't know why a low battery or bad charging circuit would make the truck idle faster.

- Jack

 

When the battery light comes on, that means that your battery is supplying the electrical power to your vehicle. Usually in conjunction with that is an alternator that is not charging, or not charging enough. The best trouble shooting I've dont is to connect your battery to a voltage regulator. With the engine running and the regulator (touching the battery) will read in excess of 14 volts if the alternator is working properly, and 12 or below if it is not. These are not exact numbers, just a guideline. If the battery is not reading 14 or more, take the alternator out and have it checked. That is most likely your problem.

Good luck.

 

Odds are, it's the altenator, then. It should be sending 14.3 or so volts to the battery. But, you can't totally rule out the battery. Occasionally, a new one can go bad.

 

why i do happen to have one but havent even thought of that. i'll check it and post what it reads. thanks

 

It's your alternator, guaranteed. Mine did the same, high idle, dimming of lights, it's blown some or all diodes and is rationing power to non-essentials. Makes sure you get or install the right size pulley, 2000's had 8-ribs vs. 6 in mid-01. Something like that.

 

i just checked the voltage across the battery while running and it only read 12.0V. Thanks

 

what else should i replace while im doing the alternator? i'm gonna replace the serpentine belt. anything else?

 

That should cover everything to do with the charging system.

 

Might want to have the battery tested. Don't know how long it has been under charged, could have paid the price by now ??

min should be 12.4 over the battery, adn the high side I think is 14.2 or 14.6 ??

The DTM on the 99-03 MY trucks have the normal band end at 15.8 I think ( senior moment myself )