Monday, April 16, 2012

Alternator getting hot on 2004 Chevy Silverado?

2004 Chevy Silverado Z-71.
In this case the alternator gets hot after driving for few minutes.

The alternator is replaced,but still gets hot.The alternator gets hot even with key off.

On basis of this details the troubleshooting is as follows:---

Its a multiple problem issue, the heating system problem and the charging system problem. I think that the charging system problem stems at the alternator. The whole getting hot with the key off and the small plug disconnected only leaves at the alternator. I know it has been checked multiple times, but the place I would start. As far as the heating system problem ,its advisable to check Heater control module. I wouldn't be too surprised if you have some shorted wires under the dash causing this type of concern.

In this problem,you will need to do some testing.
A 12 volt test light or a digital multi-meter is required to do some basic testing.

The first thing to test is the battery charge wire, this is the heavy red wire at the back of the alternator. You should always have battery voltage on this wire, even with the key off. The alternator charging is controlled by the engine control module (ECM). The ECM monitors many things and decides how much electricity is needed and then commands the alternator on accordingly.

Disconnect the alternator by just unplugging the small 4 wire (Not only 3 wires in the connector) connector, Also disconnect the big red battery wire as well? With the key on and engine off you should also see voltage on the gray wire of the 4 wire plug. Let's check these things and see where we are at.

PLEASE NOTE:--- The Service Bake Warning message by the way would be normal if the 4 wire connector were unplugged from the alternator.

The alternator should not get hot with just the big red battery wire attached unless the diodes inside the alternator were bad. If the diodes in the alt were bad the battery would be essentially back feeding the alternator and it would draw the battery down in relatively short period of time as well. With bad diodes the alt field gets energized by the battery and that would explain why the alt were getting hot even with the key off. I wouldn't think that several different alternators would have bad diodes, it is possible that something in the truck may be damaging the alt diodes soon after a new alt is connected though.

The odd thing is that there is always battery voltage to the charging lug (red wire) on the back of the alternator, and if the diodes are good then voltage does not pass through the diodes. Diodes are a electrical check valve of sorts, electricity can only pass through in one direction. So if the alt is hot even with the 4 wire connector disconnected then the problem is in the alt for sure. After disconnecting the battery the heating system would normally go through a relearn process of the actuators in the dash. If you turn the key off before the full relearn takes place, 2 or 3 minutes, then you may be inducing a fault of some sort that would default the actuator to hot. Now why it takes adjusting the time in the radio to clear that fault is a complete mystery to me. They are two totally different components and systems, they only share a data circuit and that is all.

This details will help.

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