2nd Gen Non-Engine/Transmission Voltage Issue

[wyatt1672]

The voltage on my 01 keeps dropping. It runs for about 5 minutes at around 12 volts then drops down to 8. Both batteries tested good and so did the alternator. The truck continues to run. What else should I look for?

 

[RBeard]

Does it sound like the engine is loading up when the voltage drop happens ???. If so, could your intake heater grid be coming on and staying on???. There is not much other than a short that could draw the voltage down to 8 like that.

 

[wyatt1672]

I don't know. Im not even sure how to check for that. I forgot to mention I was showing 2 trouble codes. 1682 and 1693

 

[B.G. Smith]

1682 is "low voltage detected", 1693 is "DTC detected in PCM" The votage regulator is in the PCM I believe. You probably need to connect a meter to the batteries to verify if the voltage is really fluctuating. bg

 

[JR]

How was the altenator checked? On the vehicle or did you remove it and have it bench tested? 12 volts output is not enough.

 

[Missouri Mule]

To check to see if intake heaters are on when the volts drop put a test light/volt meter/multi-meter on the cable/nut at the intake heater(s)(there are two of them).

 

[wyatt1672]

The alternator and the batteries were bench tested. I checked the volts on the batteries with the truck running and they were at 12 volts. when I put the multi-meter on the alternator it jumps to 19 then displays 0. but I might not be checking it correctly. The meter is set at 20DC and Im putting the positive on the main wire then the negative im grounding on the engine block or the negative battery post.

 

[RikDavis]

Check the battery voltage with the truck not running. Should be around 12 volts. Check again with the truck running and it should have increased to the 13.5 to 15 volt area. If no increase there is a charging system problem. If the truck is cold there may be some fluctuation as the grid heaters kick in and out for the first few minutes

 

[JR]

Check the main altenator fuses in the pdc under the hood.

Your altenator should be putting out more than 12 volts on a bench test

 

[B.G. Smith]

Check the main altenator fuses in the pdc under the hood.

Your altenator should be putting out more than 12 volts on a bench test

The big post on the alternator is hot all the time, should show battery voltage all the time. If you got a 0 voltage there then the fuse at the PDC is blown. It is a fusible link rated at around 140 amps. bg

 

[wyatt1672]

Its fixed. It was the 140 amp fuse. $4.50 and 2 minutes later everything is working right. Thanks everyone