One day at highway speeds the low voltage light went on. Pulled over to look for obvious, nothing. Restarted with no light, drove another 3 miles and light returns so I head home.

I go to Autozone and get battery and charging system checked and all checks out okay.

Put battery on trickle charger and used car for 7 mile trip later. Battery light went back on quickly, then the ABS light, then a few more including MIL light.

On way home headlights got dimmer and dimmer to completely dark but car ran pretty good with one stumble at idle. Have P0700 (tranny module) and P0562 (low volts). Tranny code likely from one hiccup.

When I checked I was getting 13.52 volts running and 12.5 engine off. The 13.52 seems low but within spec according to Haynes.

Do I have an ECM or a power control module replacement?

Something else to look at?

Is it possible for alternator to supply engine and not body lights?

Thanks for any help offered.

 

Year model and engine size please?

 

2005 3.8 liter V6 about 190k miles

edited mileage. Not 190k, 90 k

 

How does ur battery cable/terminals look? are they clean or full of green corrosion and white powders?

 

Battery is relatively new with dielectric grease on the terminals. IOW,they look great and I cleaned the ground point a while ago.

 

Sounds odd but, i had a porsche, the low voltage light came on, i bought a rebuilt alternator that did INDEED show 14 volts when revved, and 13 at idle...

HOWEVER the low voltage light STILL came on.

I wound up replacing it with a bosch factory rebuilt one SOLVED the problem.

Could be it's producing good voltage BUT UNDER LOAD it's not producing enough amps to charge the battery and run any accssories.

Could be as simple as what has been mentioned ie: bad connections or loose wires but just wanted to share my experience in case it helps.

 

Turns it was the alternator. Found out the hard way at the dealer. Little pissed off with the Autozone testing. I would have done the alternator myself had the test shown the proper problem. I guess you get what you pay for. That test was free.

 

your alternator had a bad internal diode. Nowadays it sometimes is harder to catch this if you dont have the proper equipment...just like autozone and any autoparts store...they dont have qualified techs so why would they have the proper tools

 

Would this have been caught had I taken the alternator OUT and had it tested in the stand at Autozone?

 

if they still had the older vat testers yes they would of cought it