Engine/Transmission (1994 - 1998) alternator problem... again

[Piersol]

Last year my "gen" light came on periodically but after I turned off the truck the light would always go out and the system would be charging fine. After about a month of this it finally just died. The gen light stayed on all the time and I bought a new alternator from auto zone or advance( I don't remember which one). The problem last year started when it was below zero. This week my "gen" light reappeared after being dormant for the whole year. I turned the truck off and the light quit and it is charging fine. Guess what the temperature was when the light went on. That's right; minus 1 degree. Is this coincidence? Any thoughts. That was three days ago and everything has been fine since. The code is of little help. 47(low voltage).

 

[K5IP]

You need to do some troubleshooting.

Your line fuse is probably OK, fuses arn not usually intermittant.

Since the charge rate (assuming sufficent speed), is controlled by the voltage applied to the field, this is a good place to start.

One side of the field winding gets full battery voltage as supplied from the auto shut down realy. Check to see that battery voltage i. e. 12Vdc is being supplied. If not the relay is suspect, or the PCM is not enabling it.

The second side of the field is connected to the PCM which sinks current to ground (or through some resistance) to control the charge.

If your battery is low, the PCM should lbe demanding a full alternator output by placing nearly all the battery voltage across the field winding.

Check this with a voltmeter.

If most of the battery voltage is present across the field (above 10vdc) the regulating circuit is ok and the alternator is again at fault.

If no voltage, or very low voltage is preesent across the field, the PCM is not demanding a charge current.

There are several inputs to the PCM which are necessary to make the system work. The most common fault is the engine speed sensor (hall effect switch)

or the connector just above the sensor.

Sorry, I don have my manual with me so I can not give you wiring colors for the field but be sure your tach is working to verify the engine speed sensor.



Sorry this got so long

Rog

 

[Eric_77]

I had mine act up on me with bad battery and truck at idle it would show low voltage. About 3 months later the Alt died cause and effect, I don't know.