2nd Gen Non-Engine/Transmission Electrical system?

[PVanderlugt]

So I have an issue that I might need some help with

2002 2500, driving along, no issues, DING, check gauges chime comes on.

I notice the Volt meter is hovering less then normal, and then drops of the scale on the low side, <8volt.

Truck runs normal, no issues noted, even shift into overdrive and TC lock up. Look around, in the mirrors, no smoke, continue home for another5 minutes, nothing changes. Truck runs fine, voltmeter less then 8.

Leave truck running, grab voltmeter, and check battery Voltage, 14. 5

Decided to turn truck off, but did not look at the gauges again to see if the light/voltage gauge were still inop.

Pulled codes, 0122 APPS voltage low and 1682, system charging voltage low.

Started truck back up, all is well again, charging at 14. 5 volt and check gauges light off.

2 new larger batteries last year, alternator is original.

Were I am confused is that according the FSM the chime/check gauges happens when system voltage is below 10. 9v,but if it was a simple alternator failure, wouldn't it hover around 12 v for a while before dropping?

I was worried about a massive short somewhere, but can't find anything obvious that would indicate a couple of hundred amp jumping around.

So I guess my questions are, 1, with a simple alternator failure, do you get immediately a check gauges/low voltage indication? And 2, anybody have any other words of wisdom/things to check?

I will throw a voltmeter in the truck, and if this happens again, verify indeed what the actual voltage is with the lights in the cab.

I understand that the voltage regulator is build into the ECM, any mayor issues with that?, never seemed to hear to much about regulator issues.

Thanks for the help

Pete

 

[JR]

Was this shortly after you started the truck? What was the temps?



2 things I would do check if you continue to have problems:

1) pull the altenator and have it bench tested somewhere, and if it is fine

2) have your batts load tested. Just because they are fairly new does not mean you could have a bad cell.

Also check the condition of all battery cables, including ground cables.

If both of those check out (I doubt they BOTH will) you may have a grid heater relay acting up or something similar. Typically when your PCM goes south there are more symptoms then what you are seeing, but not always.

As for the APPS code that is most likely from the low system voltage, especially if there is no intermittent throttle issues

 

[BLNRAY]

before you start pulling things off,check your electrical grounds,battery,body grounds,battery cable to block-all the grounds you can find.

 

[Cosmo]

Got a wiring schematic? Sounds like a wire went south, possibly a fuse or fusible link. If the voltmeter in the cluster isn't seeing the 14. 4 volts, that doesn't mean the alternator isn't charging.

 

[fest3er]

Before this, had you noticed the dash lights 'flickering' when you drive over a rough-ish road or when you hit sharp bumps? But almost never when you are driving on a smooth road? If so, your intake heater relays are probably weak and beginning to stick 'on'. The heaters pull down 200A; your alternator only puts out 140A. The system voltage drops while the heaters are 'engaged'.

 

[PVanderlugt]

Thanks guy, this will give me a start,

JR, truck had been running for a bit, went into town for an errant, and was on the way home ,not fully warmed up, it has been getting colder , so grid heaters are working now, but I was over 25 mph, so the grid heater should have been out of the loop, however, it might not be a bad plan to start with them. I know when they are cycling during initial start, the voltage drops down, but only till about 12 or so.



BlNray, yep, checking all wires and grounds is on my "to do list"



Cosmo, I do have the Factory manual, I will do some looking. What I don't understand is that even if the alternator quit for a bit, that the voltage would drop below 10. 9 so fast that the ECM drove the needle to 8 and turned the light on. From the description in the manual, the voltmeter and system voltage is 100% controlled and driven by the ECM, and communicated over the CANbus , so I would think that the gauge is correct, as. Long as there is no communication failures /code between ECM ang instrument panel.

Fest3er, I really had no other indications that I actually had low system voltage, lights, radio transmission, everything else worked normal, that is what baffled me, however there must have been a system voltage drop for the Apps code to set. As far as bumps, here in NWOhio there are no smooth roads:{



Well, I will do some testing and looking around, if it acts up again, I will do some more checking, I will report back with findings.

Pete