Parasitic battery drain

I'll hook my voltmeter up tonight to check it. Likely the kid at the parts store was just saying whatever he had heard. The analog gauge on the dash shows just below 14 volts, but analog gauges aren't fine tuned enough when it goes from 9 to 19 volts. It could be 12.5 volts or 13.5 volts.

I don't get any CEL light or codes thrown, just a battery discharged just below the ability to start the Jeep every 5 to 7 days. I put it on a charger for a brief charge and it starts right up. The Jeep ran a little smoother this morning after charging the battery all night and turning off all the electrical items.

I don't like throwing parts at problems, but a $100 alternator is much cheaper than a $600 PCM.

I got home and tested it at the terminals. 12.75 volts before starting. Started idling 13.25-13.4 volts. At 1800 RPM with lights on, blower motor on high, 13.35-13.5 volts

So it's close to the low end, and the voltage isn't swinging.

So alternator or voltage regulator? Can I bypass the PCM to see if the alternator voltage will go up?

I'll take the terminals off and clean again, check the ground cable and body connection and alternator connections.

After polishing all the connection I get similar results. 12.6, start no loads idle 13.35-13.5, 2000 rpm lights and fan on 13.5 volts.

No swings, just 13.5 V, running.

The last check I did was the old pull the negative battery cable off and see if it dies. I kept running. I'm not sure that's a thing with this car.

I tried one more thing. The alternator diodes are supposed to limit output to dc voltage. I switched the meter over an got an AC voltage instead of zero.

So I'll order a new alternator and try that. I'll drive the little 6 seed supercharged Mini Cooper we're going to sell until I get the new alternator installed and determine if that fixes things. It's a seriously fun little car but not good for winters here so I found this Jeep and gave my Toyota Highlander to the daughter in college to replace her Mini.

I measured an AC voltage leak. That's a sign of a diode failing in the alternator rectifier. Then the battery can drain out through the faulty diode. So I think that's my issue.

It's a $110 shipped fix. If it doesn't work, I'll move to the next step and see if I can test the original alternator off the Jeep and sell or turn it in for money. Worst case I put it on the shelf as my backup.

I tested it and the store put it on their machine and we both found potential issues pointing to the alternator.

I was expecting 14v plus under load, but need to track down the FSM and find the normal operating numbers.

My phone won't let me search the FSM so I'll have to download it to a PC to look. I don't feel like reading the entire thing tonight.

Oh and when I searched for diode problems I found it can make the radio act funny.
https://www.2carpros.com/articles/how-to-check-a-car-alternator

I tested the alternator diodes and they seem to check out. I tried the system again after driving a different car and letting it set all day. The running voltage was 13.1-13.25 v at load, so the alternator may be getting weak, but I'm almost certain I found the real issue.

I only got one key with the Jeep so I had another one made for a spare and drove with the original. The original is worn and Jeep is one of the only cars that has a setting past off. When I turned the car off I was going past off and to ACC, but the worn key let me pull it out.

The new key is nice and sharp and will not let me pull out the key when I turn it past off. This explains the intermittent behavior of my problem as I was turning the car off most of the time. Sometimes I went past off I recognized it because the radio was on, sometimes closing my door rattled the key tumbler I left partially in between off and ACC and turned things back on.

This explains my strange radio behavior and could explain the battery being dead or partially drained depending on what I had left on. It also explains why I found no parasitic load; because I had actually turned the Jeep off when I checked for it.

I swapped out my new key with the old one and will see if that fixes my issue since I can't pull it out if I turn it too far "off". If not, I'll put in the new alternator.

Old key left, new key right.

I've driven it a couple of days now and had no issues. I've noticed the internal lights are nice and bright every time I stop and get out. As bright as when I have it on the charger. This morning, I accidentally over rotated the key again and my radio, fan, and wipers stayed on, but I couldn't pull out the key until I had it in the correct position. It's going to take me a while to learn how far to rotate to off since rotating it all the way was my normal for the last 10 years.

So far, it seems my random parasitic load was simply me leaving the car on accessory when parking it. It makes sense that it happened more on the weekends because I've been working on the Jeep each weekend.

If you can pull your key out on anything except the off position, I'd recommend making a new one or potentially replacing the lock if it's not the key. Most of you have likely driven a Jeep long enough that it's not a big deal, until someone else drives it and drains the battery for you.

I went out in the garage this morning and my delay windshield wiper was running. It was raining yesterday and when I stopped the Jeep it was delayed long enough for me to leave without noticing. The Jeep started anyway.

I tested it in the parking lot at work by turning on the wipers and lining the key up to off. They of course turn off. Then I turn it to accessory and can run the wipers. I must have a little slop or wear in my lock and ignition that allows for things to stay on even with the sharper key; so I'll be replacing it. For now, I'll make sure to turn everything major off; radio, blower motor, wipers, lights, etc. when I leave it over night or at work.

I built a circuit with a buzzer for my old truck because it was old enough not to warn that the lights are on. Maybe I'll build one for this Jeep that buzzes if I leave the accessories on when the car isn't running.