Archived Over chargng on 2002, no CEL

[Sticks]

This is a first for me. In the 10 years I have been working on trucks, I have never encountered this. Even dong a search on the forums did not turn up any potential assistance.

Truck is in the signature line.

Got off work yesterday and the batteries were dead. OK, got it jump started and checked the alternator output, 14. 2V. Not great on the alternator trying to charge dead batteries, but lack of options here. I have all accessories (radio, fan, phone charger... ) turned off to keep the amperage draw to a minimum.

Hit the road and 1/4 mile from the shop the Check Gauges light comes on and the voltmeter is pegged at 18v. I am not in a position to pull over and shutdown (I know I won't get it started again either - batteries not charging long enough). After a few minuets the voltmeter returns to normal (14v) so I figure either the Alt burned up and I have about 2 minuets of drive time before I hit that 9v problem and the engine dies, or everything is back to normal... ish. Ding Ding - Check gauges light again, pegged at 18v. This cycle of over charging then return to normal continues for the 30 minute drive home. No check engine light, did not check for stored codes yet ( I know there is overboost and wheel speed error in there)

Anyone encounter this? I know the Alternator is controlled by the PCM, but I don't know what I need to be looking for to verify that the ECM is not sending a bad signal or full fielding it.

Initial plan right now is to replace the Alternator and batteries (11 years old - as in STOCK), then see how it goes. I would rather verify the Alternator control first.

If anybody has the method of bypassing the PCM for the charging circuit - external regulator or some such - pleas post it or PM me with the instructions.

 

[mwilson]

At 11 years of age I would change the batteries first before spending a dime on anything else.

Provided your connections all pass muster I am thinking that you may have a broken plate or cell connector inside one of the batteries. When that break opens the Regulator function of the PCM is seeing a low voltage situation, therefore it iallows the alternator to run full tilt in a futile attempt to restore a state of charge. When the plate makes connection the PCM is getting good info and will settle down at system voltage.

I have chased internal battery issues before and with that kind of age it would be a good place to start, again with the assumption that you have checked all connections.

Mike.

 

[Sticks]

Thanks Mike.

Batteries first, then verify charging system is OK before Alt. Just want to have both parts on hand, I'd rather make a second trip to the parts store at my convenience to return rather than a "right now".

I did find a link to fabing up an external regulator if it turns out the PCM is my problem.

 

[bigblock_doc]

Another vote for batteries. Clean all grounds, at block and all along the inner fenders. Then check with a voltmeter.

 

[Sticks]

Looks like it's going to be a weekend project. I'll post updates Sat or Sun.

 

[GAmes]

Do you have a temp sensor under the drivers side battery? If replacing the batteries doesn't do the trick, it could be the culprit. I had a charging failure while on the west coast and installed an external regulator as a temp fix. After ordering and reading a systems diagnostic manual I found out the sensor controls the charging rate by sensing battery voltage. The FSM, IIRC, shows the resistance of the temp sensor should be between 8000 and 11,000 ohms. Mine tested to 12,000+ so I ordered a new one. I haven't had a chance to install it yet, so at this time it is just a theory.

 

[HHhuntitall]

Sounds like you guys got it tracked down. I doubt the PCM is fried. It's just reading the voltage as too low and pegging it, trying to up the voltage to get a charge. And if it has the battery temp sensors, it's shutting down charge when it senses the batteries overheating. It could be the PCM or alternator overheating and shutting down, and after it cools down it comes back on. I would replace the batteries and go from there. Ironically, I just fixed an '02 last week with the same problem. He was lucky, though. His started when he came out from work... ... barely. Both batteries spewed acid out on the fender, but we caught it before it ate all the paint off.

 

[Sticks]

Neither one of them boiled, but both were down to 6. ? volts the next morning. I really should have disconnected them when I got home to make sure I don't have some sort of parasitic draw going on to make sure.

Either way, today she get's some new ones.

As far as the temp sensor, I am pretty sure I have them. I'll ohm them out then check my manual for the specs.

 

[Sticks]

So far the new batteries seemed to have solved my issue. I will take it for a longer drive today and see how it goes. Still not comfortable with the fluctuating voltage (14. 0 - 14. 7), but at least it's consistent.